Unusual event

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In my breaker box, I have two 40A breakers side by side. One is for the A/C, one is for the electric dryer.
Seemingly simultaneously, both of them experienced a loss of power (around 11V) on one leg. Thus, neither the dryer nor a/c work.
Can anyone imagine how this could happen, seemingly simultaneously?
H
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What do you mean "on one leg"? I'm assuming that the power to both the A/C and dryer is 220V.
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On a 240V circuit, each leg is 120V (or more).
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correct? 11V L1 to L2? 11V L1 or L2 to N? Please provide some more details.
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wrote:

Yes, there are two 40A double pole breakers side by side.
On both, at the breaker, it's 240V on both.
At the other end of the line, it's around 80V (combined) on both. One leg has 127V, the other measures between 11V and 18V.
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H wrote:

You still aren't telling us specifically where you are putting your voltmeter leads to measure those voltages.
And, are you using an "electronic" voltmeter subject to displaying voltages developed across its input impedance by microamp sized capacitively coupled currents, or are you using a lower impedance analog meter, not subject to showing so called "phantom" voltages?
Jeff
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I wish manufacturers would mention the Phantom Voltage issue with electronic multimeters. It would save a lot of needless frustration.
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mike wrote:

That would only help people who RTFM. <G>
Jeff
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Jeffry Wisnia
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H wrote:

Only way I can imagine this happening simultaneously is if one transformer phase on the utility pole went out. Have a look at your power meter - is the disk turning at all? If you feel safe doing so and have a decent voltmeter, you could open the service panel and check for voltage between the bus bars. Check each bus bar to the neutral line, and to each other; there should be 115 volts between each phase and neutral, and 230 between the two bus bars.
If there's not, you have a problem. My own inclination would be next to check at the terminals right on the master breaker, if they're accessible (not easy on some designs), on the house side; if you still have a loss of voltage, then I'd check on the other side of the breaker. If the problem exists on both sides of the breaker, call the hydro company. If the supply side is good but the service panel side isn't, call your favourite electrician.
WARNING: Don't do this if you are at all unsure of what you're doing! Wear electrical safety gloves rated to at least 1000 V, long-sleeved shirt and trousers (sleeves rolled down), rubber-soled boots and stand on a piece of rubber mat while you do this. Have someone stand by with a 3 or 4-foot length of wood - 2x2 will do nicely; if you have an unfinished (i.e., not varnished or painted) wooden cane, even better. Their job will be to knock you clear of the panel if something happens and you accidentally contact something.
Sorry if this is stuff you already know, but better safe than sorry - and it may be of use to others.
Yours aye, W. Underhill (who, the other day, proved the axiom that familiarity breeds contempt and as a result was bitten by 440 V on an auxiliary relay...)
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Well, I do know what I am doing around a breaker panel, but I had an electrician anyway testing the breakers. They are working perfectly. Full power on the business leads of the double breaker. The other end (at the dryer and A/C) is where the problems manifest themselves.
One thing of possible import: I am having a new room added to the back of the house, and an electrician ran a new wire into the breaker panel, though he did it rather blind (he could not see exactly where the drill came out in the basement.
It seemed to me that had he hit the 240V line, sparks (or something) would fly. None of that happened. But, if he had nicked both 240V lines, would that explain the power loss (which is not total)?
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H wrote:

Not if he cut the neutral or ground.
Open up the hole and see what he did.
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Of course, if he had hit either the neutral or the ground, that wouldn't affect the voltages on the hot legs...
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Doug Miller (alphageek at milmac dot com)
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wrote:

I agree. Instead of all this theory, he should look where changes were made.
I ddin't undderstand the story about the electrician, but drilling without seeing where the drill will come out sounds, I don't know, risky?
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mm wrote:

I've seen it happen myself - putting in the mounts for a new TV in the C&POs mess; the shipwright doing the mounting measured twice and for safety's sake put a block of 2x4 between the wireway and the bulkhead - but the block shifted and the drill went as neatly as you please into the lighting circuit for that WT compartment. No lightshow, just the lights went out.
We razzed him about it for weeks afterwards...
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On Fri, 22 Jun 2007 03:28:40 GMT, William Underhill

Phew, I thought you were going to tell me the ship sank!

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It sounds like you lost one pole of each double pole breaker. Just loosing 11 volts wouldn't stop it from working. If you lost one pole of each of those breakers you probably lost one leg of the main breaker or the entire service. In a modern breaker panel, there is pretty much no way to loose one leg of just two breakers

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Both breakers are working perfectly.

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So, you didn't lose any voltage at the breakers as you first indicated?

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I reread what I originally typed, and guess I sent the message too soon.
Yes, the breakers are fine and the power in the breaker box is fine.
The problem is at the other end of the line.

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Each of the two double pole breakers reads 240 volts at the breaker, but something less at the dryer and at the AC. What exactly is the reading across the two hot legs at the dryer and the AC?

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