The 51120 has no neutral to ground or line to ground protection from what I can see.
The 51110 has only a 20mm MOV vs 40 mm for the 51120 and the 41120.
I have seen the 51110 for around $60; the 51120, about $200; and the 41120 for around $400.
Is ground protection needed? Is the 41120 overkill for a single home? Do I need to spend $400 for adequate protection?

It's very important to me to protect all my appliances and electronics. We experience too many power failures. Desperately need advice.

Surge equipment is not going to have any affect on power failures.

If you have had equipment damaged by surges then it might be worth installing equipment, but a whole house unit is only part of the answer.

Point of use equipment is still needed.

That's great if you are home and awake.
========
"Point of use equipment is still needed."

I am interested in this problem too. With the growth of electronic controls on just about any electrical device, board blow-outs will become more common. How does one protect hard-wired equipment "locally". Why is this local protection necessary? Is it for surges generated downstream of the service panel or for further protection from surges that come down the drop because the device in the service panel is not going to do the whole job.

Very overrated as a source of damage.

The loads on the grid are just to large to have the voltage rise very quickly.

The current just does not rise all that fast.

Lightning or higher voltage distribution lines contacting lower voltage lines are a more common source.

Apparently advertising has you fearing myths. For example, power restoration does not create destructive surges. Either voltage turns on just like someone flicked a wall switch. Or voltage rises slower.

All appliances contain superior internal protection. Your concern is the rare transient (maybe once every seven years) that can overwhelm existing protection. Surges that do damage cannot be blocked, stopped or absorbed by MOVs at the appliance. What does any protection at the appliance is already inside an appliance. Your concern is a transient that can blow through existing protection. Will even blow through any adjacent protector that attempts to stop it.

No protector does protection - despite advertising that claim otherwise. Yes, read that sentence again. Either a protector connects hundreds of thousands of joules harmlessly outside the building. Or that energy finds earth ground by blowing through appliances. A homeowner's only solution is to connect that energy to earth before it can enter the building.

Best protection is when a wire connects directly to earth ground. The neutral wire already connects to earth where it enters the building. Best protection for neutral already exists IF and Only IF earthing is sufficient. A 'short as possible' connection must exist from the neutral wire to what does protection - earthing electrodes.

Other wires (ie AC hot wire, telephone) cannot connect to earth directly. So a 'whole house' protector connects destructive surges to earth. Then energy dissipates harmlessly outside. Then a surge need not find earth by blowing through appliances (and power strips).

Do MOVs do protection? Again, destructive surges are hundreds of thousands of joules. How many joules do MOVs in the power strip absorb? Only hundreds? They have you mistakenly assuming MOVs do protection. Please undo the myth. Either an MOV connects hundreds of thousands of joules harmlessly to earth. Or MOVs must somehow absorb that energy.

Protection always about where energy dissipates. Always.

Worry about the current rating of a protector. Destructive surges can be 20,000 amps. So a minimally sized (and effective) protector starts at 50,000 amps. A protector must remain functional after thousands of amps to earth ground. A protector conduct even maximum surges to earth for decades without failure. 50,000 amps is important because effective protectors must connect energy to earth - just like a wire. Only then is a surge connected to protection.

Your #1 concern should be what does protection. How good, low impedance, and short is that connection from a 'whole house' protector to earth? Due to advertising, you do not even discuss earth. If a ground wire has splices, sharp wire bends, is too long (ie 'more than 10 feet'), inside metallic conduit, or bundled with other non-grounding wires, then protection is compromised. Insufficient earthing. A safety ground wire in a receptacle is bundled with other wires. Wall receptacle safety ground does not earth any protector.

If single point earth ground is not implemented, again, compromised protection.

Leviton is one of many protectors that actually do protection because a dedicated wire connects low impedance (ie 'less than 10 feet') to earth. Like any effective protector, the Leviton connects hot wires to earth. Effective protectors need not make a 'neutral to earth' connection. Other effective solutions come from Siemens, ABB, Intermatic, Ditek, Square D, General Electric, Polyphaser, and other companies known for their integrity. A Cutler-Hammer version sells in both Lowes and Home Depot for less than $50.

Advertising is difficult to unlearn. Best protection is a wire (no protector used) low impedance to earth. Best protection for your cable TV or satellite dish wire is 12 AWG copper wire as short as possible (ie 'less than 10 feet') to single point earth ground.

Any utility wire that cannot connect directly to earth must then connect via a 'whole house' protector. The protector only acts like a wire when a direct connection cannot exist. A protector is only as effective as its earth ground.

Spend less time worrying about the simple science - a protector. Spend significantly more time worrying about what actually does the protection. Single point earth ground. And connections to that ground.

100 years ago, telephone operators removed their headsets and left the room. Then lightning did not kill them via headsets.

No, they did not leave the room. Because phone wires were earthed by protectors before entering a building. The solution was well understood over 100 years ago.

How often is your town without phone service because a lightning storm destroyed their switching computer? So your telco disconnects phone service during every thunderstorm? Of course not. It suffers about 100 surges with each storm. And no damage.

What is taught by advertising is completely different from what is installed for no damage. For example, Sun Microsystems "Planning guide for Sun Server room" defines what is always implemented when effective protection is installed:
> Section 6.4.7 Lightning Protection:
> Lightning surges cannot be stopped, but they can be diverted. The
> plans for the data center should be thoroughly reviewed to identify
> any paths for surge entry into the data center. Surge arrestors can
> be designed into the system to help mitigate the potential for
> lightning damage within the data center. These should divert the
> power of the surge by providing a path to ground for the surge
> energy.

Protectors do not do protection. A protector only connects to what does all protection - as Sun bluntly states. Even 100 years ago when direct lightning strikes did not kill telephone operators. Protection means a surge is earthed before it enters a building. Protection is always a building wide solution. Protection is always about where energy dissipates.

The IEEE surge guide is aimed at people with some technical background.

westom wrote:
"Apparently advertising has you fearing myths. For example, power restoration does not create destructive surges. Either voltage turns on just like someone flicked a wall switch. Or voltage rises slower."

Power restore is not a likely source of surges.

You can get surges from power interruptions, for instance where a recloser restores and interrupts the power.

westom wrote:
"All appliances contain superior internal protection. Your concern is the rare transient (maybe once every seven years) that can overwhelm existing protection. Surges that do damage cannot be blocked, stopped or absorbed by MOVs at the appliance."

How fortunate that protectors do not use MOVs to block, stop, or absorb a surge.

Equipment may or may not have surge protection.

westom wrote:
"What does any protection at the appliance is already inside an appliance. Your concern is a transient that can blow through existing protection. Will even blow through any adjacent protector that attempts to stop it."

Nonsense.

westom wrote:
"No protector does protection - despite advertising that claim otherwise. Yes, read that sentence again. Either a protector connects hundreds of thousands of joules harmlessly outside the building. Or that energy finds earth ground by blowing through appliances. A homeowner's only solution is to connect that energy to earth before it can enter the building."

More nonsense

westom wrote:
"Do MOVs do protection? Again, destructive surges are hundreds of thousands of joules. How many joules do MOVs in the power strip absorb? Only hundreds? They have you mistakenly assuming MOVs do protection. Please undo the myth. Either an MOV connects hundreds of thousands of joules harmlessly to earth. Or MOVs must somehow absorb that energy."

And more nonsense.

Neither service panel or plug-in protectors protect by absorbing the surge energy. (Both absorb some energy in the process of protecting.)

The author of the NIST surge guide investigated how much energy can reach the MOVs in a plug-in protector. Branch circuits were 10m and longer, and surges coming in on power wires were up to 10,000A (which is the maximum probable surge, as below). The maximum energy was a surprisingly small 35 joules. In 13 of 15 cases it was 1 joule or less. For a couple reasons, the current that can reach a plug-in protector is quite limited, so the energy that is absorbed in a plug-in protector is very limited. Plug-in protectors with much higher ratings are readily available. High ratings mean long life. A plug-in protector, wired correctly (see below), is very likely to protect from a very near very strong lightning strike

westom wrote:
"Worry about the current rating of a protector. Destructive surges can be 20,000 amps. So a minimally sized (and effective) protector starts at 50,000 amps."

Anther investigation by the author of the NIST surge guide found the maximum surge on incoming power wires that had any real probability of occurring was 10,000A per wire. There is a reference to that in the IEEE surge guide. It is based on a 100,000A lightning strike to the utility pole adjacent to the building in typical overhead power distribution.

For a service panel protector, the IEEE surge guide recommends a minimum rating of 20,000 to 70,000A, or for high lightning areas 40,000 to 120,000A (per hot wire). The protector will not be hit with those surge amps, they just mean the protector will have a long life. Use the surge amp rating of the protector, not the MOV diameter.

westom wrote:
"Like any effective protector, the Leviton connects hot wires to earth. Effective protectors need not make a 'neutral to earth' connection. Other effective solutions come from Siemens, ABB, Intermatic, Ditek, Square D, General Electric, Polyphaser, and other companies known for their integrity. A Cutler-Hammer version sells in both Lowes and Home Depot for less than $50."

Neither Lowes or Home Depot have a surge protector for $50 that has the ratings westom recommends.

All these manufacturers "know for their integrity" except Polyphaser and SquareD make plug-in protectors (that westom says don't work) and say they are effective. For its "best" service panel protector SquareD says "electronic equipment may need additional protection by installing plug-in [surge suppressor] devices at the point of use."

westom wrote:
"Any utility wire that cannot connect directly to earth must then connect via a 'whole house' protector."

A service panel protector (which vivi68 is asking about) is a real good idea.
But from the NIST surge guide:
"Q - Will a surge protector installed at the service entrance be sufficient for the whole house?
A - There are two answers to than question: Yes for one-link appliances [electronic equipment], No for two-link appliances [equipment connected to power AND phone or cable or....]. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be NO - but that does not mean that a surge protector installed at the service entrance is useless."

A service panel protector is very likely to protect anything connected only to power wires. The NIST surge guide suggests that most damage is from high voltage between power and phone/cable/... wires. A service panel protector does not, by itself, provide that protection.

westom wrote:
"A protector is only as effective as its earth ground."

Westom has an apparently religious belief (immune from challenge) that surge protection must directly earth a surge. The IEEE surge guide explains (starting page 30) that plug-in protectors do not work primarily by earthing a surge. They work by limiting the voltage from each wire (power and signal) to the ground at the protector. The voltage between the wires going to the protected equipment is safe for the protected equipment.

When using a plug-in protector all interconnected equipment needs to be connected to the same protector. External connections, like cable, also must go through the protector. Connecting all wiring through the protector prevents damaging voltages between power and signal wires.

For real science read the IEEE and NIST surge guides. Excellent information. And both say plug-in protectors are effective.

==========================================
At a service panel the neutral and ground are connected. A service panel protector has connections to the 2 hot wires and the neutral/ground (3 wires).

People may be more likely to comment on the Leviton protectors if there is a link to information.

I also agree with the comments by brickeyee.

I guess in his limited understanding there is no way to protect aircraft from surges, since a source of earth ground is not available.

Yet we manage to protect the electronics and radios (including antennas) from everything up to and including direct lightning strikes.

With no source of earth ground.

Using may of the exact same techniques and methods we use on the ground.

Read page 42 figure 8 of his IEEE citation. The IEEE defines many devices called protectors. Then shows what happens when a protector is too close to appliances and too far from earth ground. Page 42 Figure 8 - the protector earths a surge destructively through any nearby TV. It need not even be a TV connected to that protector. A protector earths a surge harmlessly when at the service entrance. Or Page 42 Figure 8 - it earths that surge 8000 volts destructively through TV2.

A surge 8000 volts destructively through any nearby appliance - TV2. Because protection and surge damage is always about the electric current path to earth. Always.

NIST also discusses protectors. Then says which ones actually do protection. bud's NIST citation says on page 17:
> A very important point to keep in mind is that your surge protector
> will work by diverting the surges to ground. The best surge
> protection in the world can be useless if grounding is not
> done properly.

The word: useless.

The OP is strongly encouraged to inspect or upgrade what makes his and any other protector effective. A low impedance connection to earth ground.

Bud says a protector does not stop, block, or absorb a surge. Correct. He forgets to mention is that a protector adjacent to any appliance can only work by stopping, blocking, or absorbing a surge. How does his protector do that when he says it does not? Or does that protector magically makes a surge disappear? He never says why his 'magic box' protector works. He is paid to promote protectors that do not even claim that protection. That even have a history of creating house fires.

Where are numeric specs for that protection? He will never post spec numbers for protection. Why? No such numbers exist. Did he forget to mention that?

The informed homeowner does what all professionals recommend. For example the IEEE even puts numbers to effective protection:
> Lightning cannot be prevented; it can only be intercepted or
> diverted to a path which will, if well designed and constructed,
> not result in damage. Even this means is not positive,
> providing only 99.5-99.9% protection. ...
> Still, a 99.5% protection level will reduce the incidence of direct
> strokes from one stroke per 30 years ... to one stroke per
> 6000 years ...

The OP is only asking about what does the 99.5% to 99.5% of protection. A 'whole house' protector. He is not asking about bud's protectors that only do maybe 0.2% of the protection? Those are numbers from the same IEEE that bud is paid to misrepresent.

IEEE Emerald Book also informs the OP what is necessary to have protection:
> It is important to ensure that low-impedance grounding and
> bonding connections exist among the telephone and data
> equipment, the ac power system's electrical safety-grounding
> system, and the building grounding electrode system. ...
> Failure to observe any part of this grounding requirement
> may result in hazardous potential being developed between
> the telephone (data) equipment and other grounded items
> that personnel may be near or might simultaneously contact.

What does the IEEE say is necessary for protection? The same thing the OP is strongly encouraged to inspect or upgrade. "Low-impedance grounding and bonding connections exist among ..." Same that I posted previously.

The OP asked about real protection - a 'whole house' protector. The only solution that all telephone companies, Sun Microsystems, and even munitions dumps require for no damage. Every professional organization including the IEEE and NIST say why the 'whole house' protector does 99.5% to 99.9% of the protection. Because it connects low impedance (ie 'less than 10 feet') to single point earth ground.

The OP and other informed consumers are encouraged to inspect earthing of a 'whole house' protector. To ignore his cheap shots. To avoid protectors the NIST called "useless". To do what every professional recommends so that damage will not occur. Effective protectors are always earthed low impedance (ie 'less than 10 feet') to single point earth ground.

Protection is always about where energy dissipates. Destructively inside appliances. Or harmlessly outside the building. A protector is only as effective as its earth ground.

Sun's Planning guide for the server room recommends one solution in "Section 6.4.7 Lightning Protection:". Properly earthed 'whole house' protectors. Not plug-in protectors.

The OP is only asking about 'whole house' protectors. Useful answer discusses what makes all protectors effective. Earthing.

Lie #1.
My only association with surge protection is I am using some surge protectors. If westom had valid technical arguments he wouldn't have to lie about others.

westom wrote:
"bud's job is to post half truths, spin, and lies to protect sales."

Lie #2
My "half truths, spin and lies" come from the IEEE and NIST.
Westom's "facts" come from his apparently religious belief in earthing.

westom wrote:
"Read page 42 figure 8 of his IEEE citation. The IEEE defines many devices called protectors. Then shows what happens when a protector is too close to appliances and too far from earth ground. Page 42 Figure 8 - the protector earths a surge destructively through any nearby TV. It need not even be a TV connected to that protector. A protector earths a surge harmlessly when at the service entrance. Or Page 42 Figure 8 - it earths that surge 8000 volts destructively through TV2."

Anyone with minimal reading and mental abilities can discover what the IEEE guide says in this example:
- A plug-in protector protects the TV connected to it.
- "To protect TV2, a second multiport protector located at TV2 is required."
- The illustration "shows a very common improper use of multiport protectors"
- In the example a surge comes in on a cable service with the ground wire from cable entry ground block to the earthing system at the power service that is far too long. In that case the IEEE guide says "the only effective way of protecting the equipment is to use a multiport [plug-in] protector."
- westom's favored power service protector would provide absolutely NO protection.

It is simply a lie (#3) that the plug-in protector in the IEEE example damages the second TV.

With no sources that agree with him westom has to misrepresent what the IEEE says.

westom wrote:
"NIST also discusses protectors. Then says which ones actually do protection. bud's NIST citation says on page 17:"

Lie #4.
Everyone is in favor of earthing building systems.
But what does the NIST surge guide really say about plug-in protectors?
They are "the easiest solution".
And "one effective solution is to have the consumer install" a multiport plug-in suppressor.

With no sources that agree with him westom has to misrepresent what the NIST says.

westom wrote:
"Bud says a protector does not stop, block, or absorb a surge. Correct. He forgets to mention is that a protector adjacent to any appliance can only work by stopping, blocking, or absorbing a surge."

Lie #5
Only believed by people who are willfully stupid.

westom wrote:
"Or does that protector magically makes a surge disappear? He never says why his 'magic box' protector works."

Lie #6
It is only magic for westom.
Repeating:
"They work by limiting the voltage from each wire (power and signal) to the ground at the protector. The voltage between the wires going to the protected equipment is safe for the protected equipment."

westom wrote:
"He is paid to promote protectors that do not even claim that protection. "

Lie #1 repeated and lie #7.

westom wrote:
"Where are numeric specs for that protection? He will never post spec numbers for protection. Why? No such numbers exist. Did he forget to mention that?"

Lie #8.
A 10 year old could find specs.
I have posted specs many times. So have others. Westom always ignores them and repeats one of his favorite lies.

westom wrote:
"The informed homeowner does what all professionals recommend. For example the IEEE even puts numbers to effective protection:
> Lightning cannot be prevented; it can only be intercepted or
> diverted to a path which will, if well designed and constructed,
> not result in damage. Even this means is not positive,
> providing only 99.5-99.9% protection. ...
> Still, a 99.5% protection level will reduce the incidence of direct
> strokes from one stroke per 30 years ... to one stroke per
> 6000 years ...
The OP is only asking about what does the 99.5% to 99.5% of protection. A 'whole house' protector. He is not asking about bud's protectors that only do maybe 0.2% of the protection? Those are numbers from the same IEEE that bud is paid to misrepresent."

Lie #9.
The 99+% figures from the IEEE "Green" book are for lightning rods. They are not for service panel protectors.

With no sources that agree with him westom has to misrepresent what the IEEE says.

westom wrote:
"IEEE Emerald Book also informs the OP what is necessary to have protection:"

The "Emerald Book" ("IEEE Recommended Practice for Powering and Grounding Sensitive Electronic Equipment") recognizes plug-in suppressors as an effective protection device.
Just like the IEEE surge guide.

westom wrote:
"The OP asked about real protection - a 'whole house' protector."

Repeating from the NIST surge guide:
"Q - Will a surge protector installed at the service entrance be sufficient for the whole house?
A - There are two answers to than question: Yes for one-link appliances [electronic equipment], No for two-link appliances [equipment connected to power AND phone or cable or....]. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be NO - but that does not mean that a surge protector installed at the service entrance is useless."

westom wrote:
"A protector is only as effective as its earth ground."

Westom's religious mantra protects him from conflicting thoughts (aka. reality)

For real science read the IEEE and NIST surge guides. Both say plug-in protectors are effective.

Then read westom's sources that say plug-in protectors do NOT work. There are none.

Or simply ,limiting the voltage potential between wires and allowing the clamping device to dissipate the power.

Luckily while surges may have very high voltage and current, their duration is limited, and energy is power multiplied by time.

I certainly agree with "delusional rantings", but westom's technobabble answers convince some people. Who would expect someone would troll the internet with information as wrong as westom. Sounds like you (and brickeyee) have a good background in electronics.

I wouldn't bet on him disappearing, unless you have a moderator. Googling for ["westom" surge] used to return around 14,000 hits. (It is lower now - I don't know what google is doing.) There are more under google groups and previous names. One of the forums I contribute to the most westom sent a technobabble e-mail instead of responding through the forum.

And I post some information that people probably don't know. Like that the maximum energy absorbed at a plug-in protector for an 'event' is unlikely to be over 35 joules. It surprised the NIST surge expert that investigated it. Even more surprising - the maximum energy is not for the strongest surges.

Explains why your posts are irrelevant to the OP's question. You did not even learn how a typically destructive surge does damage. Or how a protector works. No wonder you posted about the irrelevant (ie airplanes). Somehow your protector makes 8000 volts just magically disappear? Only in myths, advertising, and fiction.

Connect a 330 volt (power strip) protector to AC electric wires. A typically destructive surge (ie in the IEEE citation) is maybe 8000 volts on one wire. And now 7670 volts on other wires. Where is the protection? By putting thousands of volts on more wires, how does it do protection? It doesn't; as every NIST and IEEE citation stated.

Why did the NIST say an ungrounded protector is "useless"? 8000 volts on one wire. 7670 volts on other wires. Your protector is "useless" - as the NIST says.

OP asked about 'whole house' protectors. So that superior protection inside all appliances is not overwhelmed. To have what the IEEE describes as 99.5% to 99.9% protection. Where do you answer the OP's questions? Where do you quote even one manufacturer spec number that claims protection? Where do you post anything other than hearsay? You cannot post specifications because those specs do not exist. Where are those spec numbers? Crickets.

The OP is not asking about scams. So why are you recommending one? He has asked about protectors used anywhere that damage cannot happen. Every informed consumer and professional earths a 'whole house' protector for 99.5+% of the protection - at tens or 100 times less money. Then a protector does not put 7670 volts on other wires. And does not create house fires.

How does your protector magically dissipate hundreds of thousands of joules? Another damning question you ignore while also not answering the OP's questions. Somehow you just know 7670 volts on other wires is not destructive? Another victim of advertising.

"If we had a moderator..." Kurto, how about a referee?

Westom, I am not a "he". I'm a she. Just a homeowner who is replacing a lot of old appliances and concerned that today's appliances with all their electronics, are extremely vulnerable to power surges.

A few years back, we were watching TV in the middle of a storm, when suddenly the power went out. The TV went out and never came back on. It had died. We didn't, and still don't, have either cable or satellite. We do have an antenna mounted on the roof.
Another time a modem died (this was back when we had modems).

When I said I wanted a "whole house surge protector", I meant what was called a TVSS (transient voltage surge suppressor) or now, a Surge Protective Device (SPD) that is mounted next to or in the circuit breaker panel. And I do understand that what these devices do, is divert potentially damaging current so it doesn't reach your appliances and electronics (hopefully). Regardless of whether some think they work or not, I do want one because I believe from what I've read that they do. At least I prefer erring on the side of caution. The cost of just one motherboard and service call could be as much as $300. Not to mention all the aggravation that entails. I have plenty of point of-use protectors for individual electronic equipment and appliances.

Westom, whatever information or myths I've managed to glean about these devices I have not gotten from advertising. I've never seen any ads or commercials for panel mount surge suppressors - or any type of surge protector for that matter. My sources have been my homeowner's insurance company, utility companies, This Old House, a book published by Taunton, ("Wiring a House"), etc. And I only mentioned Leviton because that manufacturer's devices seem to be ubiquitous.

What I would really like to know, is an SPD like the Leviton 51120 which has no neutral to ground or line to ground protection adequate? Or do I need protection for all four electrical modes (L-N, L-G, N-G and L-L)? I do have a line from my circuit breaker panel out to a ground rod outdoors.

Also, which is better: devices that mount outside the service panel or inside, like a standard breaker?

You continue to not see that your 'earth grounding' is NOT the only effective way to provide surge protection.

And 8,00 volts is nothing.
Simple static electricity can exceed 20,000 volts.

Airplanes do not have a source of earth grounding, yet protection works just fine.

Under your ignorant model this simply cannot be.

The energy in the surge is dissipated as heat in the clamping device.

This concept is about as old as electronics.
While some surges do have extremely high energy, "How does your protector magically dissipate hundreds of thousands of joules?" many do not.

The source impedance is very high, meaning it cannot deliver that much energy into a load.

Like static electricity from rubbing your feet on the rug has a very high voltage (tens of thousands of volts) it has very low energy since the current available is very small.

Add to that your wrong assumption that all surges are earth related and earth seeking and you will not achieve all that much.

A huge amount depends on what type of surge the protection is designed to cope with.
Clamping can fail if all the conductors rise.

Luckily this is not all that common.

This does leave us with a grounded wire to shunt charge to.
While the wire may have some impedance (especially at the higher frequency of typical surges) it is still better than nothing.
The impedance decreases the effectiveness of the clamp device by creating additional voltage rise across the protected device.

Luckily it is not all that hard to provide enough capacitance within a device to store adequate charge to further limit voltage rise.

We respond when this bovine scatology shows up to try and limit its misleading and wrong assumptions.

It is rather a waste of time though.

As posted up top and as weedmeister also confirms, neutral and ground wires need no protector. Because both must already connect short to earth. Protection installed in any facility that cannot have damage connects only Hot wires to earth ground. Then all incoming wires (hot, neutral, and safety ground) have connections to earth. That is the best protection possible.

Your telephone lines should already have a 'whole house' protector installed for free. That protector was required long before PCs existed. But just like the breaker box 'whole house' protector, it too is only as effective as its earth ground. Only then can it 'divert' a surge.

Essential to protection is the quality of earthing. Something never discussed when ineffective protectors are promoted. What makes the breaker box 'whole house' protector so effective? A wire to earth (typically a bare copper quarter inch diameter wire) should be as short as possible (ie 'less than 10 feet'). Have no sharp bends. Not be in metallic conduit. Best routed separate from all other wires. And must connect to the same earthing electrode (rod) also used by the telco (installed for free) 'whole house' protector.

Protection is always about where energy dissipates. Therefore best protection for the neutral and safety ground wires needs no protector. Those wires connect directly to earth. Earthing also makes one 'whole house' protector your best possible solution. Also listed were many 'more responsible' companies that provide that superior solution.

Does not matter where the protector is located (ie breaker box, electric meter pan) as long as it makes a connection to single point earth that is as short as possible (and those other requirements). See details in my first post.

Important for a 'whole house' protector is its current rating. It should be at least 50,000 amps. As also defined in that first post.

westom wrote:
"Explains why your posts are irrelevant to the OP's question. You did not even learn how a typically destructive surge does damage. Or how a protector works.
No wonder you posted about the irrelevant (ie airplanes)."

Lie #1.
According to westom you can't protect a flying airplane that gets hit by lightning - "a protector is only as effective as its earth ground".

Brickeyee understands exactly how surge protection works.

westom wrote:
"Connect a 330 volt (power strip) protector to AC electric wires. A typically destructive surge (ie in the IEEE citation) is maybe 8000 volts on one wire. And now 7670 volts on other wires."

You do not get 8,000V from surges on power wires. For a strong surge, when the voltage at the service panel busbars reaches about 6000V there is arc-over to the enclosure. After the arc is established the voltage is hundreds of volts. Since the enclosure is connected to the earthing system that dumps most of the surge energy to earth.

If you had 6000V at the service you might have 2000V at a protector - one supply wire and 2 drain wires.

The 8000V in the IEEE example is from a surge that comes in on the cable service with a ground wire from the cable entrance ground block to the earthing system that is far too long.
A service panel protector will provide NO protection.
And the IEEE guide says "the only effective way of protecting the equipment is to use a multiport [plug-in] protector."

westom wrote:
"Where is the protection? By putting thousands of volts on more wires, how does it do protection? It doesn't; as every NIST and IEEE citation stated."

Lie #2
It is part of an IEEE surge guide example that shows how plug-in protectors work.
A plug-in protector protects the TV connected to it.

The only 2 detailed examples of protection in the IEEE surge guide use plug-in protectors.

westom wrote:
"Your protector is "useless" - as the NIST says."

Lie #3
Repeating what the NIST surge guide really says about plug-in protectors:
They are "the easiest solution".
And "one effective solution is to have the consumer install" a multiport plug-in suppressor.

westom wrote:
"To have what the IEEE describes as 99.5% to 99.9% protection."

Lie #4
The percentages are the effectiveness of lightning rods, not service panel protectors.

westom wrote:
"Where do you answer the OP's questions? Where do you quote even one manufacturer spec number that claims protection? Where do you post anything other than hearsay? You cannot post specifications because those specs do not exist. Where are those spec numbers? "

Lie #5.
If specs were posted westom would immediately deny they exist, like he always does.

westom wrote:
"How does your protector magically dissipate hundreds of thousands of joules?"

Often explained but westom's mental blinders prevent him from absorbing anything that conflicts with his religious belief in earthing.

For real science read the IEEE and NIST surge guides. Both say plug-in protectors are effective.

Then read westom's sources that say plug-in protectors do NOT work. There are none.

Everyone here that has posted agrees at least that service panel protectors are very likely to protect from anything that is connected to only power wires.

The NIST surge guide suggests that most equipment damage is from high voltage between power and cable/phone/other wires. A service panel protector, by itself, does not protect from this. A plug-in protector will, but all interconnected equipment needs to be connected to the same protector and external connections, like cable, also must go through the protector. (That should include your antenna if you connect your TV to a plug-in protector.)

You don't say if your TV failure was after a lightning strike. It could have been a power line surge from a strike. Or a very near strike can induce a damaging surge on the antenna wire. Or there can be surges from the power failure.

(If a tree branch comes down on a power wire and there is a fault that blows a fuse, the high fault current stores energy in the inductance of the power wire that can produce a surge when the fuse opens.)

The coax from your roof top antenna should go through a ground block where it enters the building. The ground block has to be connected to the building earthing system. The connecting wire should short. It is still possible to have high voltage between the coax center conductor and the shield which the ground block will not protect from, but that is more likely with cable.

vivi68 wrote:
"Westom, whatever information or myths I've managed to glean about these devices I have not gotten from advertising."

Westom is an internet nut. Some of what he writes is obvious nonsense. Lots of luck picking what is good from the drivel.

vivi68 wrote:
"What I would really like to know, is an SPD like the Leviton 51120 which has no neutral to ground or line to ground protection adequate? Or do I need protection for all four electrical modes (L-N, L-G, N-G and L-L)? I do have a line from my circuit breaker panel out to a ground rod outdoors."

As weedmeister wrote (and I wrote in my first post) N and G are connected at the service and the surge protector does not need separate N and G connections.
The ground rod is connected to both the N and G at the service.
(Ground rods are not a very good earthing electrode.)

If you provide links to your surge protector information you might get some comments about them.

I provided suggested surge amp ratings in my first post. You could also look them up in the IEEE surge guide.

vivi68 wrote:
"Also, which is better: devices that mount outside the service panel or inside, like a standard breaker?"

Either should be good.

External is probably cheaper and you can get higher surge amp ratings.

Anything you use should be listed under UL1449.

It decreases their power handling ability, resulting in them breaking over into conduction next time and then failing open from the current they are trying to carry.

There is no simple way to verify how much current handling remains available.

If you are in an area that gets a lot of surges (most commonly form lightning) periodic replacement is about the only practical option.

he ones with indicators they are still working do not actually indicate how much damage is present, just that they are not presently failed.

There is not anything much you can do to protect everything against nearby direct lightning strikes.
The panel itself is likely to have significant damage, along with the conductors in the grounding electrode system, and possibly the feed into the panel, the meter, etc.

Short grounding electrode conductors with as few bends as wide as possible provides a better path for lightning.

Sharp bends create magnetic field crowding on the inside of the bend, increasing the impedance of the path and resulting in lightening seeking a lower impedance path.
It will try to 'go straight' despite the wires bend, and may flash over to another nearby path with a lower impedance.

The fast rise times of the pulse causes them to not behave like typical 60 Hz power, but are much closer to radio frequency power.

Testing high current surges is a little scary as any wires not fastened firmly in place will jump around under the forces generated by the magnetic fields of the large currents.

You can seethe same thing happen when a power distribution line has a fault and may tens thousands of amps of fault current flow briefly till the line protection opens.
The line will jump and move around under the huge forces created by the fault current.

Defense in depth remains the best solution for a home that may experience surges.

All conductors (phone, cable, antenna feeds, power) entering need some type or protection, and then additional protection at sensitive devices like computers (and their accessories (like printers), wide screen TVs, stereos, anything with significant electronics.

Manufacturers have gotten better at protecting their control electronics, but mainly from events the device generates internally.
Refrigerator compressors pull significant current at start-up, and control wiring exposed to the magnetic field created needs to be protected so it does not carry anything into sensitive electronics.

It decreases their power handling ability, resulting in them breaking over into conduction next time and then failing open from the current they are trying to carry.

There is no simple way to verify how much current handling remains available.

If you are in an area that gets a lot of surges (most commonly form lightning) periodic replacement is about the only practical option.
__________
MOVs have a joule (energy) rating which is the single event energy that puts the MOV at its defined end of life (but still functional). If the energy hits are much smaller, the cumulative energy rating is much higher. For example a MOV might have a (single event) rating of 1,000 joules. If the individual hits are 14 joules the cumulative energy rating might be 13,000 joules. High ratings give a much longer life than you might expect.

Francois Martzloff, the NIST surge guide author, looked at the maximum surge that had any reasonable probability of occurring. It was 10,000A per service wire, and is based on a 100,000A lightning strike to an adjacent utility pole in typical overhead urban distribution. (Only 5% of lightning strikes are stronger, and the strike was extremely close.)

Martzloff also found that with power surges up to 10,000A (the maximum above) the energy absorbed at a plug-in protector was only 35 joules maximum. In 13 of 15 cases it was 1 joule or less. (I can find you an on-line paper on this if you want to read it.)

One of the plug-in protectors I am using has 3 MOVs, each rated 590 joules (30,000 surge amps), 1770 joules total. The MOV ratings are so far above 35 joules the cumulative rating will be far higher than 1770 joules. That is one reason the manufacturer has a protected equipment warranty on it. I do not expect that this protector will fail.

(The 30,000 surge amp rating (90,000A total) just goes along with the high joule rating. You can't get a surge anywhere near that even at the service panel.)

The normal failure mode of a MOV is it starts to conduct at normal voltages (after any surge) and goes into thermal runaway. UL has, since 1998, required thermal disconnects for overheating MOVs. The IEEE surge guide describes, for a plug-in protector, that the protected equipment can be connected across the MOVs, or be connected across the incoming power wires. If connected across the MOVs the protected equipment will be disconnected on failure. That is another reason why manufacturers can have protected equipment warranties.

For service panel protectors the IEEE has suggested ratings that were in my first post. They are well above the 10,000A maximum probable surge. High ratings again mean long life.

Martzloff has written "in fact, the major cause of [surge suppressor] failures is a temporary overvoltage, rather than an unusually large surge." An example of overvoltage is crossed power wires. While MOVs can handle thousands of surge amps for the maybe hundred microsecond duration of a surge they are rapidly burned out by much longer lasting "overvoltage".
==========

brickeyee wrote
There is not anything much you can do to protect everything against nearby direct lightning strikes.
__________
The maximum surge with any reasonable probability of occurring is 10,000A per power service wire (as detailed above). (There is a reference to 10,000A in the IEEE surge guide.) Service panel protectors with much higher ratings are readily available. Everything I have read is that you can protect at the service panel from a very near very strong lightning strike.

And even with no service panel protector, a plug-in protector is very likely to protect from the same 10,000A power wire surge. But it must be connected correctly. Interconnected equipment has to be connected to the same protector, and all external wires including phone, cable, .... have to go through the protector.
**********************

brickeyee wrote
The panel itself is likely to have significant damage, along with the conductors in the grounding electrode system, and possibly the feed into the panel, the meter, etc.
__________
The wires involved can carry the currents involved for the short duration of a surge. (Maximum probable current to the earthing electrodes is 30,000A - 10,000A each for hot, hot, neutral service wire.)

If a strong surge raises the voltage at the panel to about 6,000V there is arc-over from busbars to the enclosure. After the arc is established the arc voltage is hundreds of volts. Since the enclosure is connected to the earthing system that dumps most of the surge energy to earth. The energy at the arc is (hundreds of arc volts) times (10,000A max probable surge on power wire) times maybe 100 microseconds. My understanding is that there is not likely to be significant damage.

There can also be arc-over at the meter enclosure that likely protects the meter.

Crossed power wires are a different matter.

And a direct strike to the building requires lightning rods for protection - but you are not talking about a direct strike.
==========

brickeyee wrote

The fast rise times of the pulse causes them to not behave like typical 60 Hz power, but are much closer to radio frequency power.
_________
Continuing the logic, for that reason the inductance of wire is more important than the resistance. A 30 ft wire in an example in the IEEE surge guide has a 10,000V drop. That is why there need to be short wires connecting phone and cable (and other) entry protectors to a common connection point on the earthing system, and a short distance from that point to the N-G bond at the power service.

And it is also one reason why the energy at a plug-in protector is so low - 35 joules max. The voltage at the panel is about 6,000V max because of arc-over. Then the inductance of the branch circuit greatly limits the current, and thus energy, that can reach the protector.
==========

brickeyee wrote
You can seethe same thing happen when a power distribution line has a fault and may tens thousands of amps of fault current flow briefly till the line protection opens.
The line will jump and move around under the huge forces created by the fault current.
__________
Sounds like fun. Where do I apply for a job...
==========

brickeyee wrote
Defense in depth remains the best solution for a home that may experience surges.

All conductors (phone, cable, antenna feeds, power) entering need some type or protection, and then additional protection at sensitive devices like computers (and their accessories (like printers), wide screen TVs, stereos, anything with significant electronics.
__________
It is what everyone (with one exception) agrees is the best protection.

(I edited out a lot of your post that I agree with.)
==========

Except that each one decrease the maximum energy that can be handled, and lowers the break over voltage slightly.

You can end up with a device that will open circuit while high voltage is still present, resulting in downstream damage.

It takes a vanishingly small amount of actual energy to damage many electronics.
Even micro-amps at a high voltage can destroy semiconductors in a single pulse lasting a few nanoseconds.

"maximum surge that had any reasonable probability of occurring"

If he only considered lightning he failed to account for distribution line problems like falling wires.
The fault current in the grid is far in excess of 10,000 amps per wire.
Composite interrupt ratings are higher for this reason.

Lightning is rather nasty, with multiple strokes in a single strike, and a huge range of voltages and currents (2 kA to 250 kA, Integral i^2dt from 6E3 to 1.5E7 A^2s, and flashes from 0.15 ms to 1.100 seconds).

"The normal failure mode of a MOV is it starts to conduct at normal voltages (after any surge) and goes into thermal runaway."

And then fails open, by accident or design.

I have spent over 30 years now designing protection for electronics, including 'operate through' systems (operate during occurs more by luck with smaller strikes).

TELCOs have needed better and better protection as they have switched from mechanical stepper relays to electronic switching.
A pulse that might barely tickle the old mechanical systems can wreak havoc if it get very far into the electronic central offices now in common use.
One of the isolation methods is to take local loops and multiplex them onto a fiber optic link withing the CO.
The vulnerable equipment is isolated from the local loops.

"Only 5% of lightning strikes are stronger, and the strike was extremely close."

The 5% limit for a negative first stroke and flashes is 150 kA, and 250 kA for a single positive flash.

And it can hit all the way up to the service drop on the side of the house.
There is not reliable way to protect from these strikes in a residential setting.

Service equipment is often destroyed.
The service drop from the weather head serves as a crude guide to a final earth flash, with damage to the panel and interior wiring of the house not all that uncommon.

Buried lines are significantly better (not very likely to be struck directly, and the line insulation often fails at extreme overvoltage if distribution lines are struck and it gets past the transformer).

"My understanding is that there is not likely to be significant damage."

The arcing over in the panel creates damage in and of itself depending on the exact path it takes.

The flash can damage insulation on wires in the panel, damage circuit breakers (especially GFCI and AFCI devices with electronics), and even cause fires in panels.

It is not a pretty sight to open and examine a panel that has received a nearby stike.
"And a direct strike to the building requires lightning rods for protection - but you are not talking about a direct strike."

And there are far more houses without rods than with, meaning the building itself and its utility wiring is an easy entry point.

I remember watching a 3 story townhouse that was struck with extensive fires ignited throughout the attic and top two stories.
We watched the whole thing from strike to the FD getting it under control from out nearby 6 story office building (we had already had antennas, transmitters, receivers, lab equipment, and even some upper floor building wiring damaged from a failure to bond the rebar in the building adequately during construction).

Within the 3-4 minutes for the FD to respond (semi-rural area) the attic and third floor had become fully involved, with flames starting to exit some second story windows.

The firewall to the adjacent unit held up adequately, but the entire unit was declared a loss and then demolished down to the basement slab and then rebuilt

"Then the inductance of the branch circuit greatly limits the current, and thus energy, that can reach the protector."

But the inductance also serves to increase the voltage created.
Free lunches remain unavailable.

brickeyee wrote:
Except that each one decrease the maximum energy that can be handled, and lowers the break over voltage slightly.
__________
Geez - someone intelligent to talk to.

But the MOVs still function and limits the voltage. The cumulative energy rating still increases (as can be seen from characteristic curves for MOVs). (I am assuming in all cases MOVs are used on power wiring. There are different problems if you are using them on, for instance, telephone wiring.)
==========

brickeyee wrote:
You can end up with a device that will open circuit while high voltage is still present, resulting in downstream damage.
__________
They are open circuit after catastrophic failure. Normal failure for MOVs on power circuits is conduction on normal voltage and thermal runaway. The thermal disconnects required by UL since 1998 disconnect the overheating MOVs before catastrophic failure. Msrtzloff says catastrophic failure is more likely caused by overvoltage (discussed below) than a "surge".
==========

brickeyee wrote:
It takes a vanishingly small amount of actual energy to damage many electronics.
Even micro-amps at a high voltage can destroy semiconductors in a single pulse lasting a few nanoseconds.
__________
Sure.

Risetimes of surges coming in on power, phone, cable service wires are limited by the inductance of the supply wiring. MOVs are fast enough for any such surge. Some other devices, like gas discharge tubes aren't since they require an arc to be initiated.
==========

bud wrote:
"maximum surge that had any reasonable probability of occurring"

brickeyee wrote:
If he only considered lightning he failed to account for distribution line problems like falling wires.
The fault current in the grid is far in excess of 10,000 amps per wire.
Composite interrupt ratings are higher for this reason.
__________
As I wrote, crossed power wires are not "surges" and you can not rely on either service panel or plug-in protectors for protection. They are not designed for it. (There are some plug-in protectors that are supposed to disconnect on overvoltage, and a UPS may safely disconnect.)
==========

brickeyee wrote:
Lightning is rather nasty, with multiple strokes in a single strike, and a huge range of voltages and currents (2 kA to 250 kA, Integral i^2dt from 6E3 to 1.5E7 A^2s, and flashes from 0.15 ms to 1.100 seconds).
__________
I have not seen data on surges anywhere near 1.1 seconds. The probability of a surge that is beyond 10kA is very low and the probability of protector failure is correspondingly small. Martzloff has argued that long surge events would result in far higher incidence of protector failures than is seen.
==========

bud wrote:
"The normal failure mode of a MOV is it starts to conduct at normal voltages (after any surge) and goes into thermal runaway."

brickeyee wrote:
And then fails open, by accident or design.
__________
On power circuits catastrophic failure occurs after thermal runaway at normal voltages. UL required thermal disconnects disconnect failing MOVs before they catastrophically fail open.
==========

brickeyee wrote:
I have spent over 30 years now designing protection for electronics, including 'operate through' systems (operate during occurs more by luck with smaller strikes).

TELCOs have needed better and better protection as they have switched from mechanical stepper relays to electronic switching.
A pulse that might barely tickle the old mechanical systems can wreak havoc if it get very far into the electronic central offices now in common use.
One of the isolation methods is to take local loops and multiplex them onto a fiber optic link withing the CO.
The vulnerable equipment is isolated from the local loops.
__________
I agree vulnerability of all the new electronics is a challenge.
Fiber optic (and wireless) makes protection of equipment with connection to both power and signal a lot easier. When you move out of a house and into an extended commercial or industrial setting problems with different ground reference voltages become a lot greater.

I expect most people here are interested in residential.
==========

bud wrote:
"Only 5% of lightning strikes are stronger, and the strike was extremely close."

brickeyee wrote:
The 5% limit for a negative first stroke and flashes is 150 kA, and 250 kA for a single positive flash.
__________
Every source I have read is the percentage of all lightning strikes that are over 100kA is about 5%.
==========

brickeyee wrote:
And it can hit all the way up to the service drop on the side of the house.
There is not reliable way to protect from these strikes in a residential setting.
__________
But the probability is extremely low.

That is the point of the 10kA figure (which is also in the IEEE surge guide) - there is a very low probability of a worse event. The figure I saw was once in 8000 years. It is not practical to design anything for the worst possible case.
==========

brickeyee wrote:
Service equipment is often destroyed.
The service drop from the weather head serves as a crude guide to a final earth flash, with damage to the panel and interior wiring of the house not all that uncommon.

Buried lines are significantly better (not very likely to be struck directly, and the line insulation often fails at extreme overvoltage if distribution lines are struck and it gets past the transformer).
==========

bud wrote:
"My understanding is that there is not likely to be significant damage."

brickeyee wrote:
The arcing over in the panel creates damage in and of itself depending on the exact path it takes.
__________
The arc voltage is, if I remember right under 500V, but call it 500. Assume 10kA surge current for 100 microseconds. The energy is 500 joules. That is the energy from a 120V 4A load for 1 second. Panel damage does not seem as likely as it would seem.
==========

brickeyee wrote:
The flash can damage insulation on wires in the panel, damage circuit breakers (especially GFCI and AFCI devices with electronics), and even cause fires in panels.

It is not a pretty sight to open and examine a panel that has received a nearby stike.
__________
But again probability of major damage is low.

A service panel protector with a high surge current may have a let through voltage high enough to damage AFCI/GFCI breakers. I have no idea what their withstand voltage rating is.
==========

bud wrote:
"And a direct strike to the building requires lightning rods for protection - but you are not talking about a direct strike."

brickeyee wrote:
And there are far more houses without rods than with, meaning the building itself and its utility wiring is an easy entry point.

I remember watching a 3 story townhouse that was struck with extensive fires ignited throughout the attic and top two stories.
We watched the whole thing from strike to the FD getting it under control from out nearby 6 story office building (we had already had antennas, transmitters, receivers, lab equipment, and even some upper floor building wiring damaged from a failure to bond the rebar in the building adequately during construction).

Within the 3-4 minutes for the FD to respond (semi-rural area) the attic and third floor had become fully involved, with flames starting to exit some second story windows.

The firewall to the adjacent unit held up adequately, but the entire unit was declared a loss and then demolished down to the basement slab and then rebuilt
__________
As I said, to protect from a direct lightning strike you need lightning rods (now called air terminals), which is not what the discussion has been about.
==========

bud wrote:
"Then the inductance of the branch circuit greatly limits the current, and thus energy, that can reach the protector."

brickeyee wrote:
But the inductance also serves to increase the voltage created.
Free lunches remain unavailable.
__________
There is inadequate information on what you have in mind.

The inductance of the branch circuit limits the current. It will somewhat lengthen the duration of the surge.

But the fact remains that with a 10,000A surge on the incoming power wire the maximum energy absorption at a plug-in protector was 35 joules. The maximum was not even for the largest surges. The largest surges forced the voltage at the service above 6kV and arc-over. For some smaller surges (with the shortest branch circuits) the MOVat the protector held the voltage at the panel below 6kV and there was no arc-over. One of them resulted in the maximum energy of 35 joules. The voltage at the panel was higher than the stable arc-over voltage but lower than 6kV.
==========

Ditto.

I'll have to read all the references in this thread when I have time. I generally consider surge suppression more a life-protection device, there's no guarantee it'll save an appliance, especially when we're talking about lightning-induced surges.

I did wonder about the relevance of the diameter of the MOVs the OP was talking about.

I suppose if you're keen you can crack the box open and replace the MOVs which are the most important components, I'd replace any capacitors at the same time.