Return to the Electrical Wiring Forum | Post a Follow-Up

 o
Help me understand the value of a circuit ground

Posted by civ_IV_fan (My Page) on
Fri, Jun 17, 11 at 9:19

Okay, so here is a question that applies to most old houses.

The service panel is new, updated, a ground rod is installed, etc. New circuits are easily and effectively grounded if pulled. Yet, most circuits are not grounded simply because the wire pulled is a 2-wire variety.

User has a computer plugged into a legal GFCI "no equipment ground" outlet. Although user may not be vulnerable to shock, equipment still has no path to ground and is vulnerable to surges.

Now let's say that an electrician installs a whole-house surge protector.

Now, the user is protected from shock and the equipment is protected from surge, overcurrent, etc. What value is added by having a ground wire connect the receptacle to the service panel?


Follow-Up Postings:

 o
RE: Help me understand the value of a circuit ground

You add short circuit protection, i.e., a means to trip the breaker should the hot contact the neutral or ground, or anything connected to the ground.


 o
RE: Help me understand the value of a circuit ground

There is a fairly extensive list of equipment that is required to be connected to an equipment ground when that equipment is installed in a dwelling. A 2 prong GFI protected receptacle does not provide the required equipment ground. One of the items on the list is information technology equipment, which would include computers.

A "whole house surge protector " should not be relied upon for the sole protection of electronic equipment. Past studies have shown that the majority of transients come from within the building and a whole house device will not likely clamp at a voltage level low enough to provide complete protection. Point of use protection is also needed.


 o
RE: Help me understand the value of a circuit ground

my experience is that the GFCI also provides short circuit protection - ie it trips if hot touches neutral or ground. is this not true?


 o
RE: Help me understand the value of a circuit ground

> What value is added by having a ground wire connect the
> receptacle to the service panel?

Its primary purpose is human safety (not for surge protection). It does not do anything for surge protection. But that ground may also provide other minor advantages.

For example, two interconnected appliances connected via a same safety ground are less likely to have ground loops.

Interconnected appliances are designed to make irrelevant voltage differences between those two appliances. But all solutions are implemented in layers. Another layer that protects from that damage occurs when both appliances connect to a common ground - ie the safety ground. A voltage difference that should not be destructive also does not exist.

Two minor advantages. Both also accomplished if both interconnected appliances share a common power strip powered by the GFCI two wire circuit.


 o
RE: Help me understand the value of a circuit ground

what human safety does the ground provide that the GFCI does not? if the GFCI trips whenever in voltage does not equal out voltage, then I don't understand how there is still a threat to human safety solved by having a ground.

this ground loop business seems to be the crux of the value of a ground in the situation i initially described. i read a little of the theory behind it (new to me) and it makes sense. not a safety issue but certainly a performance issue with respect to interconnected devices (eg audio equipment).

the other issue brought up by tom is that most surges come from WITHIN THE HOUSE. I did not know this. but wouldn't the surge have to not only come from within the house but within the same circuit? or could an equipment surge have a cross-circuit effect?

this is a very interesting discussion.


 o
RE: Help me understand the value of a circuit ground

Let's make it simpler. civ_IV_fan, if a live conductor inside an appliance comes in contact with the outer metal housing of the appliance, the housing becomes energized at line voltage. Would you rather the voltage (and current) imposed on that housing passes to ground through you or through a conductor dedicated to that function?


 o
RE: Help me understand the value of a circuit ground

Because you're assuming the only place that could be a hazard came through the GFCI. On much equipment it keeps things from becoming energized whether from the circuit that is feeding it or something else.


 o
RE: Help me understand the value of a circuit ground

GFCIs operate by making sure the curent on the hot and neiutral match within a very few milliamps (around 6mA, or 0.006 amps).

For the most part you are pretty unlikely to touch a hot and a neutral and receive a shock with all the current staying nice and balanced.

Yes it could happen, but it is a pretty rare case.

Without a ground connection you only have protection from a surge between the hot and neutral.
normally the hot and neutral are also tied through MOVs to the ground.

By keeping all the lines close in voltage to each other the equipment might never see anything, even if all 3-wires rose to 1,000 volts.
The voltage between them is limited by the protection device(s).

You can still have a failure, but transformers used in most electronics have a decent insulation rating.

The ground prevents anything from having a significant voltage preset you could touch, and also supplies a path that CAN conduct enough current to trip a breaker (or blow a fuse).

Actual short circuit current can easily range into the 100's to thousands of amps for the few milliseconds it takes the breaker to trip.

The panel and its breakers are rated to open correctly with ~10,000+ amps flowing in the circuit.+

The POCO is a VERY low impedance source.


 o
RE: Help me understand the value of a circuit ground

> if the GFCI trips whenever in voltage does not equal out voltage,
> then I don't understand how there is still a threat to human
> safety solved by having a ground.

Not voltage. If a 'current' incoming on one wire is same as 'current' outgoing on another wire, then no current is flowing dangerously through your body. A mismatch means 'current' is going where it should not. If a GFCI is working, then human safety exists.

Any surge created inside a house is made irrelevant by one 'whole house' protector. It protects from all types of surges. Other plug-in protectors only claim to protect from surges that are not typically destructive.

If surges are created inside, then you are replacing dimmer switches, digital clocks, and radios hourly or daily. All electronics contain protection so superior that any internally generates transient is only noise. Again, how often every day are you replacing damaged smoke detectors and GFCIs? Never? Because noise from appliances is touted as surges only by myths.

A 'whole house' protector further protects from all types of surges. Including transients that can actually overwhelm protection inside appliances. That rare transient occurs maybe once every seven years. And is made irrelevant by protectors that connect short (ie 'less than 10 feet') to single point earth ground. Earthing that is located adjacent to an AC electric box and all other incoming wires. Earthing is not provided by safety grounds in receptacles.

Superior protection costs about $1 per protected appliance. Others have a history of attacking because they cannot back up their claims with facts and numbers. If their solution is valid, then where are manufacturer spec numbers that claim that protection? never provided. I will probably ask that question repeatedly because they will ignore it. Even the manufacturer does not claim protection from the typically destructive type of surge. They are reciting advertising. Not recommending what is done in every location that cannot have surge damage.

But again, if surges are created inside, they how often per day do you replace new electronic light bulbs? Never because those appliance generated surges are myths promoted only by advertising.

GFCI does human safety protection IF it is not damaged. Just another reason why informed consumers properly earth only one 'whole house' protector. It costs about $1 per protected appliance. To even protect the GFCI. A damaged GFCI can no longer do human safety.


 o
RE: Help me understand the value of a circuit ground

The last time I checked, the IEEE (Institute of Electrical and Electronic Engineers) was still recommending two levels of protection, one at the service entrance and at each point of use.


 o
RE: Help me understand the value of a circuit ground

> The last time I checked, the IEEE (Institute of Electrical and Electronic
> Engineers) was still recommending two levels of protection

Which is only a subjective conclusion. Additional facts and numbers from the IEEE often get ignored. From IEEE Green Book, a Standard entitled 'Static and Lightning Protection Grounding':
> 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 ...

Get 99.5% protection by properly earthing only one 'whole house' protector. That costs about $1 per protected appliance. And spend $25 or $150 on power strips for what - another 0.2% protection?

In IEEE papers and other sources. Without one 'whole house' protector, power strip protector fires are possible. As even demonstrated in the IEEE brochure, a power strip protector can make appliance damage easier - 8000 volts destructively via TV2. Page 42 figure 8.

Earth one 'whole house' protector to make all types of surges irrelevant (unfortunately only 99.5% of the protection). Then spend $hundreds more for how much more protection?

Power strips without an earthed 'whole house' protector claim to do what? Even the manufacturer will not discuss it in numeric specs. Power strips are for a type of surge that is not typically destructive. But, yes, for 100% protection, one can even spend money for that maybe 0.2% additional protection. An earthed 'whole house' protector is necessary even for power strips to be useful.


 o
RE: Help me understand the value of a circuit ground

Given the range and variability of lighting strikes asserting anything is "99.5-99.9% protection" is academic BS with no relation to the real world.

There are general levels for lightning strikes, but no one claims anything better than about 95% (meaning 5% of strikes will exceed the value).

Peak current is 150 kA for negative first strike and flashes, 30 kA for negative following strokes, but moves up to 250 kA for posisitev4e flashes with no data on following strokes.

The charge moving around is 24 Coulombs 1st stroke, 11 C for following strikes, 40 C for negative flashes, and 350 c for positive flashes.

Imppulse charge is 20 C fro negative first, but 150 C for positive flashes.

Time to peak current can be as fast as 1.8 microseconds (5% level) to as long a 18 microseconds (95% level) with positive flashes taking up to 200 microseconds (95% level).

dI/dt (kA/microsecond) ranges up to 120 kA/microsecond for negative following strokes and flashes.
The first stroke creates a channel that can carry much more current for following strokes.

flashes can range from 0.15 microseconds (5%) to 1100 microseconds.

The integral (i^2dt) can reach 5.5E5 A^2 s for negative first strokes and flashes, and 1.5E7 A^2 s for positive flashes.

For most residential applications the most you can really do is try to minimize the damage that WILL occur, and if you still have an actual antenna it is even worse.

Typical residential antennas are NOT large enough to avoid damage, and there down wires are just about always pathetic.

Even ham antennas rarely survive unscathed from a strike.

I have seen nice burn marks that followed the down wire on both TV antennas and ham antennas.
Some have been damage to the siding of the house, while others are the vaporized down wire.

After these currents pass nearby you are going to have a lot of damaged electronics in the house from the induced voltages from the rapid magnetic field changes that occurred.

They are NOT insignificant.
Both the induced current and voltage can damage electronics and wiring itself.


 o
RE: Help me understand the value of a circuit ground

> Even ham antennas rarely survive unscathed from a strike.

Myths are widespread and easily promoted. Meanwhile, Alan Taylor of the US Forestry Service documented that well over 95% of trees struck by lightning even have no appreciable indication. Direct lightning strikes without damage is routine. Damage is even less likely when items (ie ham antennas) are properly earthed. Only hearsay and emotion deny that reality.

Hyperbolic claims have been made by ignoring facts and experience. A professional discusses reality:
> Well I assert, from personal and broadcast experience spanning 30 years,
> that you can design a system that will handle *direct lightning strikes*
> on a routine basis. It takes some planning and careful layout, but it's
> not hard, nor is it overly expensive. At WXIA-TV, my other job, we take
> direct lightning strikes nearly every time there's a thunderstorm. Our
> downtime from such strikes is almost non-existant. The last time we went
> down from a strike, it was due to a strike on the power company's lines
> knocking *them* out, ...
> The keys to effective lightning protection are surprisingly
> simple, and surprisingly less than obvious. Of course you *must* have a
> single point ground system that eliminates all ground loops. And you
> must present a low *impedance* path for the energy to go.

Another professional who says what makes the OP's 'whole house' protector so effective. Unsupported and subjective accusations of unavoidable damage and useless earthing does nothing to answer OP's question about adding a safety ground.

Assumed destructive transients created inside a building comes from another subjective claim not supported by facts. His 'whole house' protector and superior protection already inside every appliance also makes that noise less problematic.

Damage from direct lightning strikes is so routinely and easily averted that damage is considered a human failure. Often found where one assumes a 'woe is me' attitude. OP has earthed a best solution available to every homeowner. Advantages of a safety ground are an unrelated topic.


 o
RE: Help me understand the value of a circuit ground

very great thread, thanks to everyone who responded to my inquiry. reading this and following up with some of my own research, i feel pretty good about the existing two-wire cable + whole house surge protection (with a good, usable earth) + GFCI.

the point about whole house surge actually protecting the GFCI itself is very interesting and something i hadn't thought of. as an aside, i'm noticing that today's GFCI's claim to shutdown if the GFCI protection is compromised for some reason.

of course, old houses have other electrical issues not so easily solved such as all original wiring on a single circuit, insufficient circuits in kitchens and bathrooms, damaged knob and tube, etc. etc.


 o
RE: Help me understand the value of a circuit ground

> i'm noticing that today's GFCI's claim to shutdown if
> the GFCI protection is compromised for some reason

Long was a serious concern. Old technology GFCIs (for example those based upon the National Semiconductor LM1851) would fail (stop doing any human safety protection) without indication. Second generation GFCIs will not reset if internal electronics are damaged. Old tech GFCIs still exist. Homeowners should be aware of that problem.


 o
RE: Help me understand the value of a circuit ground

"Alan Taylor of the US Forestry Service documented that well over 95% of trees struck by lightning even have no appreciable indication. "

Then how did he determine they were struck?

I have some pieces of a telephone pole in my office that I was on less than 5 minutes before it was struck.

The top 5 feet or so of the pole was blown to splinters.


 o
RE: Help me understand the value of a circuit ground

> Then how did he determine they were struck?

Just because observation saw an exception means lightning always blows everything to splinters? That proves researchers lie? Plase stop using observation as fact. Knowledge only from observation is classic junk science. Observation also proved spontaneous reproduction. Elementary school science taught how observation alone creates bogus conclusions.

Routine is for lightning to strike without appreciable damage. Catastrophic damage comes from, well, again what the professionals say. Colin Bayliss in "Transmission & Distribution Electrical Engineering":
> Although lightning strikes have impressive voltage and current values
> (typically hundreds to thousands of kV and 10-100 kA) the energy
> content of the discharge is relatively low and most of the damage to
> power plant is caused by 'power follow-through current'.

Lighting creates a destructive path. Then a high energy source (AC utility power) creates a 'follow-through' current that causes massive damage.

Or Dr Uman:
> Most of the energy available to the lightning is converted along the
> lightning channel to thunder, heat, light, and radio waves, leaving only
> a fraction available at the channel base for immediate use or storage.

Lightning damage is considered a human failure because its energy is so easily diverted; its damage so easily averted.


 o
RE: Help me understand the value of a circuit ground

"Lightning damage is considered a human failure"?

Where do you get this stuff?

Please feel free to play golf during the next thunderstorm and test your theory about the energy content of the lightning discharge being relatively low.


 o
RE: Help me understand the value of a circuit ground

Energy insufficient to light an conventional bulb hurts like hell - or kills. As my assistant proved today when he grabbed a hot wire. Energy that cannot even light a bulb is massive energy? Of course not. Why are you posting that?

Because it hurts, then it must be high energy? Death means a few milliamps through a golfer's heart. A few milliamps proves high energy? Please. Stop using urban myths or pain to replace science.


Lightning damage is so routinely averted as to be considered a human failure. Even a priest playing the best game of his life is struck by lightning - and lives. Caddy Shack. Or are you also adverse to well known examples? How does brickeyee explain why a priest struck by lightning lives? Posting nasty in this thread to encourage god's wrath will not achieve suicide. Just wondering if he also knows that?

Because it hurts means it must be high energy? When did reality change?


 o
RE: Help me understand the value of a circuit ground

"Just because observation saw an exception means lightning always blows everything to splinters? "

"Alan Taylor of the US Forestry Service documented that well over 95% of trees struck by lightning even have no appreciable indication. "

95% is pretty far form "an exception."

It would be more like the most common occurrence.

"...most of the damage to
> power plant is caused by 'power follow-through current'."

We are not talking about power plants.

"Lighting creates a destructive path. "

So is it destructive or not?
One of your 'experts' has claimed it doe s nothing to 95% of trees.

"Or Dr Uman:
> Most of the energy available to the lightning is converted along the
> lightning channel to thunder, heat, light, and radio waves, leaving only
> a fraction available at the channel base for immediate use or storage."

Until it hits something.
Then that object must contend with "typically hundreds to thousands of kV and 10-100 kA."

If these folks represent the state of knowledge in academia for lightning issues no wonder you are confused (and in some places simply wrong).


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Electrical Wiring Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here