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Practical ways to protect appliances against unstable power

Posted by mudworm (My Page) on
Fri, May 18, 12 at 13:12

Recently, our power in the neighborhood for whatever reason has not been stable. It would go out for a split second and then come back. It doesn't happen all the time, but did happen a few times recently. My computers and routers are protected by an APC, which worked out beautifully.

I already installed a surge protector at the 200Amp panel, but apparently, it does nothing in this situation. I wonder what's the best code compliant way of protecting expensive appliances against such frequent fast power outage especially now that I'm in the last stage of wiring for the kitchen remodel.

Code requires dedicated circuits, so I have a home run 240V/50W for cooktop, 240V/30W for oven, both of which require direct connection (via wire nuts instead of plugs) and a 120V/20W for MW Oven, etc. I'm hoping to have a way to sustain the appliances for a few seconds to bridge the <1 second of power outage or can have time to shut them down normally if the power outage stays.

Any pointers for me to research into? Thank you!


Follow-Up Postings:

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RE: Practical ways to protect appliances against unstable power

A surge protector isn't going to help with outages, it may save you from transients when things cut back in. Most of your appliances should not be affected by such glitches. Turning power off doesn't hurt them. A few second outage and then turning the power back on might be a little painful to refrigeration units.

Even my whole house generator takes a few seconds to kick in after the power drops. I have these power conditioner/20 minute UPS devices I got cheap that keep most of the home electronics online in the transition.


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RE: Practical ways to protect appliances against unstable power

I would contact the utility company and ask them to look into the cause of the problem.


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RE: Practical ways to protect appliances against unstable power

The equipment to bridge even a short drop out under large loads is VERY expensive.

Where it is required a VERY large UPS and a backup generator are used.

The UPS covers for the time it takes the generator to come up to speed.


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RE: Practical ways to protect appliances against unstable power

Short of a UPS and generator, is there equipment that will manage a disconnect and then only reconnect (the whole service, automatically) when power is stable? It seems to me that a lot of damage could be avoided that way, but feel free to tell me that I am wrong about that. Casual observations over the years indicate to me that there are may instances of voltage and possibly frequency variations that result from damage and these sometimes last for a few seconds before the utility can recover regulation.

"I would contact the utility company and ask them to look into the cause of the problem."

I did that once. I was experiencing a lot of instability over a few weeks in an urban area. One day I got fed up and called the POCO figuring that there was some issue that they should look into. A shot time later I POCO worker rang my doorbell. He was obviously upset and told me that the glitch that prompted my call resulted when a worker was electrocuted on a pole nearby. Note that it was not a POCO worker but something like telephone or cable.


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RE: Practical ways to protect appliances against unstable power

Power going on and off is not by itself that much of a hazard.

The falling and rising voltage waveforms are rarely steep enough to cause damage to anything.

Compressors (mostly refrigeration) are on of the few things that could be damaged by fast off-on cycles, but almost all contain adequate built in protection since it is a well known problem (a refrigeration compressor may have liquid in the cylinder following a brief off cycle without enough time to equalize the high and low sides).

When the ultimate in availability is required, standby generators will be up and running all the time, just waiting to have the load switched to them.


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RE: Practical ways to protect appliances against unstable power

I have tons of old VHS tapes, home recorded, that I am transferring to DVD as time permits. Even a slight power interruption results in a DVD that is not finalized, cannot be finalized and will not accept additional recording. Useless. Sometimes the source material on the first part of the DVD is no longer available and thus is lost when the power fails. Quite annoying.


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RE: Practical ways to protect appliances against unstable power

"I have tons of old VHS tapes, home recorded, that I am transferring to DVD as time permits."

Use an 'on line' UPS to run the setup.


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RE: Practical ways to protect appliances against unstable power

Home computers should have a UPS, minor power glitches can cause all kinds of problems beyond writing DVDs


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RE: Practical ways to protect appliances against unstable power

As suggested, I am getting a UPS for only the DVD recorder although the process I use also involves a TV as a monitor and the VCR. If the power goes out and is restored before the UPS charge is exhausted or if the recorder is stopped properly before the UPS is exhausted, the DVD will be able to be finalized and played. And that will satisfy most of my needs.


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RE: Practical ways to protect appliances against unstable power

I once worked for a company that made a box that would serve this purpose. It contained an invertor/charger and 15kwhours of batteries. It would provide up to 30amps at 120V for about 3 hours. (There was also a device for getting 120/240V if you wanted it.) The solar version could handle up to about 5kw of PV (to charge the batteries).

You could make something like it yourself if you were into solar power. The inverter was an off-the-shelf unit. The batteries were AGM telecom but one could use wetcell lead-acid.

It cost around $25k at the time. It was also a UL-approved 'appliance' which made installation and electrical inspection simpler than a typical solar installation.


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RE: Practical ways to protect appliances against unstable power

This is a very timely question. Since roughly the time of Hurricane Irene (August 2011), my utility power has had several ridiculous anomalies. Actually it might have started a little before, but definitely in the past 15 months. I don't mean some little sag or spike. I mean:

1) During clear weather conditions, one night all the lights get very, very dim. Flat Panel TV shuts off completely. I go look at my computer UPS...its fan is running and its alarm starts going off. The incoming voltage reading is 60V! I go to find my cell to the power company. Finally after about 5 minutes, full power comes back. A brown out to SIXTY VOLTS? Aren't they just supposed to turn it off at some point? Fortunately, my refrigeration seems to have had no lasting damage. There have been a couple more brief (5 second or so) major sags, but scenario 2 is more common.

2) Several times, including yesterday which is why I'm making this post, I'll see my lights flicker if they are CFL, and become super bright if they are incandescent. My room's fan will start to sound like it's been supercharged. I look at my UPS this time, 139V! Not a 1 second surge, but, again, 3 to 5 minutes of 139V! WTF? How can their equipment be so poorly regulated?

Weedmeister is probably correct, I think, in implying that solutions to such nonsense are very expensive. The surges > 120V but < 200V are going to be a non-issue with consumer electronics powered by modern switching power supplies. Most can handle 100V to 250V for international use. From what I can glean on the web, there's no whole house surge unit that kicks in so low. They all need a surge > 300V to do anything, and they aren't voltage regulators, they are only designed to handle a brief surge.

Have the utilities completely given up on providing steady voltage? (I know some people in the DC area were thinking the same thing after their extended outages from the 'derecho' storm of last month) I've had UPS units that indicate incoming voltage for over 10 years, and I've only seen this nonsense in the last 15 months. A spike or sag during a storm I can understand...random, complete change in voltage unrelated to any storm I have not. What worries me about both scenarios is, what is it about their electrical distribution system that even permits this to happen? I feel like sooner or later, there's going to be a perma-surge to 240V, and it is going to cause my fridge motor to blow up or something.


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RE: Practical ways to protect appliances against unstable power

For the most part th edistribution network has no regulation bult into it at all.

The generators (actually alternators now) ar ethe only thing that adjusts.
They feed a system that is very much a cxolleciton opf passive equipment.

Right voltage in, right voltage out.

There are fuses and circuit breakers in the network to protect it from damage, along with some equipment to limit lightning and try to clamp very high voltage surges.

Unless the POCO has installed newer 'smart meters' they often cannot even tell if any particular customer has power.

Look up 'CBEMA curve' for a typical example of what is considered 'normal' power distribution.

This is a curve used by equipment manufacturers as a 'needs to survive' type curve.


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RE: Practical ways to protect appliances against unstable power

"The generators (actually alternators now) ar ethe only thing that adjusts. "

Well, exactly. That's what makes a sudden brownout to 60V so strange. All North American generators run synchronous with respect to frequency. They can't "bog down" and produce less voltage, if they slow down they go offline because they can't sync. A slow brownout implies a line issue somewhere increasing resistivity and thus lowering powering. (P=I2R) With an instant one to 1/2 voltage, clearly there's a transformer or switching issue somewhere. It seems like the tap malfunction that leads to an immediate switch to 60V could lead to an immediate switch to 240V. In further reading since my first post, I've read that this does happen sometimes. Fortunately, very rarely.


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RE: Practical ways to protect appliances against unstable power

My first ever UPS arrived today. I plugged it in about 8 hours ago and it seems to be functioning properly but I have not yet tripped the circuit breaker to simulate a power outage. It is 550VA, 300 watts. The load imposed on it today has been less than 25 watts. It feels barely warm to the touch. But it has an odor similar to hot phenolic. Is this normal or expected? Is this probably temporary? This is intolerable for my situation.


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RE: Practical ways to protect appliances against unstable power

The odor when I place my nose next to the unit is similar to Lysol. The odor in the room in general is a little different from Lysol. The odor is not hydrogen sulfide, with which I am familiar.


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RE: Practical ways to protect appliances against unstable power

Are you chemically sensitive or something? Many new electronic appliances seem to make this odor, "hot phenolic" is a reasonable description although it's really more like "warm urethane" from the sealants used on the circuit boards. It will wear off in a few days.


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RE: Practical ways to protect appliances against unstable power

This odor is quite strong, permeates the whole house.
Mine is a Tripp-Lite.

Here is a link that might be useful: Discussion


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RE: Practical ways to protect appliances against unstable power

Posted by davidrt28
The incoming voltage reading is 60V! I go to find my cell to the power company.

Are you still look for your cell phone???


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RE: Practical ways to protect appliances against unstable power

"It seems like the tap malfunction that leads to an immediate switch to 60V could lead to an immediate switch to 240V."

Voltage falls if winding turns in a transformer are removed from the circuit.

The ony way to increase voltage is to add turns, or short a low voltage line to a higher voltage.

Since the US Edison system uses a center taped secondary to create the 120/240 V pair, the loss of the center tap connection can allow the voltage to not divide evenly.

One of the 120 sides will approach 240 V while the other drops an equal amount.

It is a serious problem, and if you notice incandescent bulbs suddenly brightening you should turn off your main breaker and call the POCO immediately.

It is enough of an emergency they should respond quickly and will try to see if the problem is on your side of the meter or their side.

An intermittent neutral connection is areal problem and a safety hazard.


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RE: Practical ways to protect appliances against unstable power

One thing that is not regulated well is Voltage. +/-10% would not surprise me.

What is regulated well is Frequency.

What Brick said about shutting down your power is correct. I would be reaching for the main breaker rather than my cell phone.


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RE: Practical ways to protect appliances against unstable power

+/10 on voltage (long term) is pretty standard.

Do a search on 'CBEMA curve'


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RE: Practical ways to protect appliances against unstable power

Based on the extreme voltage fluctuations in both directions, and the lack of poco action, I strongly suspect, as mentioned, a poor neutral connection at your location, NOT a widespread poco issue.

An entire neighborhood dropping to half its normal voltage is NOT something that would go unnoticed or unaddressed. As mentioned, the only way the poco voltage is dropping that low is due to resistive loss somewhere (the tap changer theory is a fail: it wouldn't stay "wrong" for that long a period of time, and it sure as heck wouldn't go unnoticed), which means that, for every watt of power being consumed by someone on that line, one more watt of power would be heating up a wire somewhere. Unless you tell me you looked out the window and the power lines were glowing bright orange, I'm reasonably certain this did not happen.


Regarding your 'protection': LOW voltage is not a "surge" and you cannot expect any sort of "surge protection" to do anything about it. Such protection works for overvoltage. Undervoltage correction requires a UPS (or a line conditioner - which, in its simplest form, is basically a small-scale transformer and tap changer) - one simply cannot make up those extra 60 volts from nowhere.


Again, do not continue to ignore this problem. Someone (be it the power company or an electrician of your hire) needs to inspect all of the connections on your service - from the pole to the panel - as I'd bet most anything that one of your neutrals is loose or corroded. Once it completely lets go, some of your 120V appliances are likely to see close to 240V.

Some of the appliances you mentioned (cooking stuff) run on 240 anyway. Ironically, thus, the ones you're concerned about are probably the ones worthy of the least concern.


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RE: Practical ways to protect appliances against unstable power

The isue with a loose neutral it that when one leg goes down to 60 V, the other leg goes up to 180 V.

The two legs WILL total to 240 V at all times unless a major fault (short circuit) is loading down one leg or a transformer has developed short in its output (seondary0 winding.

A loose neutral at your pole connection, weather head connection, meter base, or even in your panel is not all that uncommon.

Since one leg can approach the full 240 V it is an actual emergency an should be fixed immediately.

Shutting off you main would be warranted until the problem is found and repaired.


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just continue here I guess

Sorry, I'm bumping this because I realized I reposted about this. I think when people started making idiotic comments about my cell phone I stopped reading.

Pharkus, help me to understand something. The center-tap pole transformer on the other side of the neighborhood has legs A & B or however they designate them that are at 120V w/respect to both [local] ground & neutral. These legs travel separately into everyone's homes, along with a neutral. At the very least, neutral again connects with ground in everyone's service panel, and, I believe, at several points along the poco line is grounded again just to be sure. (In other words, unlike in a home, ground for the power company is always supposed to == neutral. In a home, for safety reasons, they are only connected in the panel.) What I can't understand is how the status of my neutral can ever make a difference, other than a gross malfunction that would trigger a breaker to trip. I have a wire with 120V of potential. I have another with 120V offset by 180 degrees. It only interacts with the other wire at 120V potential in an appliance that is using both. (I was not running my clothes drier at the time and that's the only 240V device I have.) In other words, my panel is NOT a center tap transformer and every connection between a hot leg & neutral is through a resistive, circuit-breaker-protected appliance; the electricity will either return to neutral or return to ground. I can understand how either leg could drop below 120V due to a bizarre problem in the panel, but I can't understand how my panel or ground could make them unbalance with one going higher. Without some kind of transforming/regulating device to induce this imbalance, it seemed a breaker would have to blow in any imbalance scenario that originated locally. (i.e., anywhere downstream of the transformer) The "main breaker" is just a 2 pole breaker where, of course, the 2 poles are entirely separate but both either capable of tripping the breaker.
Let's assume a scenario where the power company only sends out "hot" lines...I believe this is actually true in rural parts of the commonwealth like NZ or South Africa. Even then, if there's a bad point-of-use ground...yes...you would have a kind of a brown-out, because there wouldn't be a complete earth return to the generator. But I still can't see how the voltage can ever go higher unless something goes wrong at the point where it's split, i.e., the transformer.

BTW, I also think the imbalance scenario is unlikely because nothing seemed to be over-voltaged. The entire house was browning out - or in the briefer over-voltage incidents, over voltaging. If I'd heard my ceiling fan speed up at the same time a light in the bathroom was dimming, that would have really freaked me out.

IF this is too exhausting, feel free to just tell me "you're wrong"...and I'll check with my favorite PhD holder in electrical engineering the next time I talk to him.

Update...I skimmed through this:
http://electricalnotes.wordpress.com/2012/07/28/impact-of-floating-neutral-in-power-distribution/

But this is mainly talking about commercial 3 phase distribution. For the neutral beyond the transformer to have been the cause of my immediate-on, immediate-off 5 minute brownout, it seems I'd have to assume 1) my panel ground suddenly failed 2) all the power line's grounds suddenly saw high resistance to ground 3) all my neighbors ground-to-neutral connectors massively failed at the same time too 4) these events all occurred in perfect sychronicity.

BTW inside my panel all 3 mainline connections looked good & tight (I didn't touch them to be sure LOL) and the ground connections looked tight too.


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RE: Practical ways to protect appliances against unstable power

Again to make it perfectly clear, I can understand how the pole transformer's neutral/ground being bad definitely would cause the voltage to imbalance. That part I understand. What I don't understand is how it could imbalance anywhere else, practically speaking (i.e., every ground connection is not going to be severed instantly).

This post was edited by davidrt28 on Wed, Jan 9, 13 at 6:47


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RE: Practical ways to protect appliances against unstable power

I found this:
http://diy.stackexchange.com/questions/12545/power-companys-neutral-cause-surges-and-brownouts

OK, I can see how this could cause a problem. But it supposes a lot: It suppose you have both a bad ground, and a bad neutral utility connection, and it also supposes you do something to induce a local imbalance that hadn't existed before. In my case, a huge, sudden something. Since neither applied in my case and I hadn't just turned on a major appliance, I think the sudden brownout was neighborhood wide, and was somehow related to a problem in their transmission network.

Here is a link that might be useful: http://diy.stackexchange.com/questions/12545/power-companys-neutral-cause-surges-and-brownouts


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RE: Practical ways to protect appliances against unstable power

If you have a loose neutral connection between you and the pole center tap that is grounded the voltage no longer splits evenly.y depending on the loads present on each leg.

The earth portion of the grounding system is a very poor conductor at 120 V.
The connection to earth at a service entrance is for lightning and pole transformer primary leakage (the earth works well at 7,200 V).

At 120 V you could drive stakes into the earth four feet apart and not get 15 A to flow between them (See 'Worm Getter', a now banned device)

Very few residential panels are 'balanced' in their loads on each leg, and i it happens to be balanced it it likely to change within a few minutes.

The resistance of conductors allows the center of the 120 V pair to wander from 0 V.
They are not perfect conductors.


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RE: Practical ways to protect appliances against unstable power

That's interesting, I didn't know ground was so resistive at low voltage. I wonder if it's something local about the the conductor to substrate interaction, or the overall path. (i.e., maybe a huge copper-plated sheet buried in the ground would provide adequate grounding of 120V. Because the surface area of the rod is quite low.) BUT! That just underscores the problem was more likely a loose neutral (assuming the lineman they sent out actually believed the brownout was caused near my residence, which I still think is hooey, and that he perhaps should have checked my service panel or told me to get it checked? (this is regarding my other post about what happened after I called the "poco") I think the huge brownout was pretty obviously caused by the line-to-line transformer situation you described. The shorter pulsings upward to 140V sound more like an imbalance scenario; except that when they've occurred I've never noticed anything dimming at the same time.


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