Unusual event

Have you measured the voltage at the output of the breakers, in the breaker box, when the AC and dryer are attempting to run?

Are the bad voltages you've given us at the receptacles? Or somewhere else nearby? And are they when the AC and dryer are attempting to run, or when they are OFF?

They may be, but it bothers me that you keep saying they are both wroking perfectly. AFAICT, all you have done is measure the voltage at the output end of the breakers. There is more to working perfectly than that. Like, Do they both trip at right current?

Not that any other problem would necessarily be related to the problem you're posting about, and not that I can help you much with it, but on principle and practice it bothers me that you keep saying they are working *perfectly*. It also makes me think you are vulnerable to missing something.

Not if he cut the neutral or ground.

Open up the hole and see what he did.

Of course, if he had hit either the neutral or the ground, that wouldn't affect the voltages on the hot legs...

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

I'm betting L2 is open somewhere along its path and you're using an electronic voltmeter which is responding to a current being capacitively coupled from L1 to L2 and displaying that current as "11 volts between L2 to neutral".

Similarly, the L1 to L2 reading is low because of the open on L2 and the voltmeter is being "measured" through the high impedance of the capacitive coupling between L2 and neutral.

If it was me seeing that 11 volts between L2 and neutral, I'd stick the fingers of one hand across the voltmeter probes and watch that voltage drop to zero. But I won't advise you to do that because some nervous Nellie on this group would scream you could get "burned" is the open on L2 magically reconnected at just that point in time.

Having recently celebrated my 50th college reunion, I remembered the Brit Professor who taught our sophmore course in "Rotating Electrical Machinery". We were mucking around with motors and generators and 3 phase power in the lab when he said, "You men will never become real engineers until you learn how to "take" a shock.

Jeff

I wish manufacturers would mention the Phantom Voltage issue with electronic multimeters. It would save a lot of needless frustration.

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?

Assuming the voltages were measured with an electronic VOM I'd say that L2 is open between the breaker panel and the load. Most likely your electrician cut or drilled through it.

Note that a 220/240V load doesn't care about the neutral; it only cares about L1-L2.

That would only help people who RTFM.

Jeff

keep in mind the OP says he has two double pole 40 amp breakers and two cables, one to the dryer and one to the A/C unit. Both cables show the same low voltage at the load ends. He also says a continuity test shows all conductors are continuous

I guess it's possible that the cables were one on top the another, and the electrician drilled through both of them at the same time.

Maybe he made a mistake on that somehow. Maybe some alternate path he didn't exclude.

A lof of maybes but something has to explain this strange problem.

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...

Well, unless he's got a multi-amp tester floating about, he's not going to be able to test the tripping current.

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

Folks,

Firstly, thanks to all responders.

The problem was caused by the contractor who installed the line for the new addition. He did, in fact, slice cleanly through the two 240V lines that were behind the wall into which he drilled the hole.

The 11V, I was told by an electrician, actually means zero, since just about anything, including one's own skin, has that much electricity in it. So, despite the fact that I said continuity was tested, that was before I understood that 11V could mean zero.

The original contractor came in and repaired it, firstly by cutting a hole in the ceiling in the basement so he could see and confirm the damage, and then by going upstairs into the kitchen, cutting a hole in the wale above the problem and putting in a box in which the old lines were (presumably correctly) spliced onto a new leads to go to the breaker box.

We have A/C and a dryer again, for which my bride is extremely grateful.

Glad you found it. That's pretty amazing, not to mention pretty bad luck. The other thing that I find amazing, is that someone could cut through two

What RBM said

Not only that, you didn't understand what it means to check continuity, and maybe you still don't. You don't check continuity by finding 120 volts at one end and 11 at the other. Or even by finding

You coudl do this either by connecting two wires in the same cable at one, and measuring the resistance between the two of them at the other end. It should be zero or substantially less than an ohm. OR By running your own wire from your owhmmeter to the far end of the wire, and the other wire/test lead from your ohmmeter to the near end of the wire, and measuring the resistance. It should also be zero or at least substantially less than an ohm. If you use a continuity tester, you can find continuity if the buzzer buzzes or the light glows.

You should never have told us you tested for continuity. Especially since that statement confused people. All you did is test for voltage, and you should have told us the details of that, but not used the word continuity.

But thanks for getting back to us. Much appreciated.

Utterly incorrect on all counts. Please, next time learn how to use a voltmeter and ohmmeter before asking for help.