Unusual event

What do you mean "on one leg"? I'm assuming that the power to both the A/C and dryer is 220V.

I assume you have two 40A double pole breakers side by side, is this correct? 11V L1 to L2? 11V L1 or L2 to N? Please provide some more details.

On a 240V circuit, each leg is 120V (or more).

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.

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

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...)

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)?

It sounds like you lost one pole of each double pole breaker. Just loosing

Both breakers are working perfectly.

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

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.

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?

L1 to L2 around 80V L1 to N - 127V L2 to N - 11V

It's the same at the air as the dryer? Are these breakers new or existing? are they full sized breakers or mini breakers?

Is that after the breakers? Sure isn't much else in you panel that could be faulty.

Same at both.

Full size breakers. Both are working perfectly. Each breaker is about 5 years old (after a heavy up).

Are the cables that go from the breakers to the dryer and airconditioner continuous, or are there junction boxes

In theory, continuous, but they were laid 40 years ago, and I cannot see exactly where they go.

Note that they were working perfectly until about a week ago, and simultaneously failed.

It sounds like you lost one leg of each cable, but I can't imagine how that could have happened. At this point you'd need to disconnect each cable from the breaker and at the load end, and do a continuity test to verify each conductor

Already done, and there is continuity, but the power down the "bad" leg is bad.

I'll tear apart the wall near where the electrician ran the new wire, and see if he possibly nicked both of the lines.