Troubleshooting a Down Line (Residence)

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zeero3

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Location
San Francisco, California, USA
120/240V Single Phase Service (Residence)
GE Panel with 16 breaker slots and 90A main located at meter bank outside
(Top 4 breakers on line A, next 4 breakers on line B, etc)
Guessing residence (condo) was built in the 1970s
Raceways are conduit or flex (no romex).
No ground wires.

Issue:
Line A goes down when a line to neutral circuit on line A is used (issue does not consistently recreate)
What I mean by this is that if a light (that is on a line A circuit) is turned on, the issue may occur, though is random.
According to what I've seen, line A has never went down when a line B circuit was used.
Line A has also never went down when a 240V circuit was energized (they have 2 240V electric heaters and a 240 range).

KICKER:
When line A is down, turning the 240V electric heater ON brings line A back up. Can shut the 240V heater off immediately after and line A stays back up until it goes down again by turning on a light on line A. Also, no breakers ever trip and I've yet to see any frayed or burnt wires anywhere.

What I've done so far:
Guts were loose in the panel so I cleaned the panel. This consisted of making sure to bolt guts down properly. Checking the bus for oxidation or anything out of the ordinary. Checked each breaker. Reattached lines A and B and neutral. Reconnected and labeled all branch circuits. Removed an illegal bonding jumper from panel to neutral bar. Removed all neutrals from the neutral bar and tested to make sure all branch circuits were independent of each other. Made sure all neutral were independent of each other and not improperly tied together downstream. Labeled neutrals and reconnected to neutral bar. Checked for any other objectionable current paths by testing continuity between branch HR neutrals to outgoing conduit it is run in (only one found was for the 240V range). Capped both 240V heater circuits at the heaters and shut off both of their two pole breakers. (Thought there might be an issue at the heater's wiring due to age and temperature changes so I eliminated this to find out, now their hack solution to bringing the A line back up is moot.)

My thoughts:
Utility company came out and everything is fine up to the meter. First thought was that it was the main breaker, but every time I have a guess at something upstream of the panel, I keep saying "but how would turning on the 240V heater bring line A back up?" I didn't find a neutral that needed to be separated (I initially was thinking this was the issue). I'm a little bit stumped and frustrated and I've talked to a few other electricians at work. Has anyone heard of something similar? A line A light (dining room or kitchen) seems to be the most common culprit so my next step is to replace the switch. Loose connections at the main sound reasonable as well, but not when I remember about the 240V heater bringing line A back up. When everything is up line-to-neutral (both lines) is 123V and line-to-line is about 213V.

I know this is a lot, but I wanted to give as much information as I could to see if this rings a bell for anyone. Thanks in advance to anyone that has a lead.....
 
So, it sounds like you have asked one or more local journeymen?
And recognize that in terms of troubleshooting you are over your head?
Happy to try to help as long as you recognize your limitations in actually correcting something on your own.

1. Since A voltage disappears some or all of the time when you put a load on it and certain other conditions are not met, it seems pretty clear that there is an interruption in the A path to the loads somewhere. Not likely to be only a neutral problem in any way from what you describe.
2. If A voltage to neutral is gone, then something causes it to reappear, what might that be?
a. If you close a 240V load (and a heavy, low resistance one at that) it will provide a path from A to B and will allow B to energize the isolated part of the A wires. You are measuring near normal from A to neutral, but I will bet that you measure close to zero from A to B downstream of the break.
I keep saying "but how would turning on the 240V heater bring line A back up?"
Click to expand...
There you are! :)

b. If there is also a broken neutral, then turning on a B to neutral load downstream of both breaks will put that just turned on B load and the non-working A load in series from the B line through its neutral to the A line, A load, and a different section of the neutral wire that is still connected. Pretty complicated, but might match some of your symptoms.​

I would tackle the open A wire first. Turn off all loads and with a low input impedance meter or a wiggy measure the voltage at receptacles or outlets connected to A until you find the place where the voltage goes away. This might be in a feeder somewhere or it might be between meter and main panel or in one pole of the main breaker.

Once you have discovered and repaired that, check to see if there are any remaining strange problems that might indicate a broken neutral somewhere, which you can then search for. Caution: If you suspect a broken neutral, trying different combinations with expensive loads (appliances, TVs, etc.) connected would be a very bad idea. None of them would like 240V at all. A continuity tester with the main off and zero voltage on A and B verified may be a better approach.
 
Yes, I've asked multiple local JWs and recognize that troubleshooting this particular issue has me and many others stumped.

When line A goes down, it goes down from the load side of the meter. I totally agree with your line of reasoning on 2.a. you laid out. However, when line A goes down, A-to-neutral is 0V at the main lug on the panel, at the load side of the main breaker (located outside at the meter bank), and the line side of the main breaker/load side of the meter--it goes down after the meter, not just after an expected break in line A.

I also follow your line of reasoning on 2.b.

Since the line A voltage break is located between the line and load side of the meter, I will start by checking the back of the meter socket again. That was one of the first things I checked and saw nothing out of the ordinary.

Also, when it comes to neutrals, none are lost. I shut off the main breaker and shorted outlets, lights, etc to make sure all neutrals returned. I really appreciate the response and I'll update. Troubleshooting is a love/hate....
 
Welcome to the forum. You need a methodical method to troubleshooting problems, even the hardest ones, which are intermittent.

As GoldDigger already wrote, when a high amperage draw, low resistance, purely resistive 240V load is energized, and let's say the A leg is completely disconnected at the panel, the B leg will backfeed thru the equipment, thru the breaker, and energize the A buss. If this were to happen, your 240V load, like a water heater, would not operate at all*, it would simply act as a jumper from B to A buss. You also would have 0V or thereabouts from A to B in the panel.

*If there are line to neutral loads on the A leg, the water heater would then have a complete circuit thru those loads, however it would operate very poorly.

Personally, I would normally start with where the problem is noticed: kitchen and/or dining room lights. Switches are always suspect. Move the switch not just up and down, but torque it a bit side to side, and operate it slowly right where it makes/breaks the circuit. Loose connections in switch boxes are another common failure point. Is it one light or several? Receptacles too? The more things that dont operate correctly or at all puts the problem closer to the service vs branch wiring.

I also would see if it is one or maybe two branch circuits, or everything on the A leg.

If you have verified everything in the panel is correct, and the POCO says everything 'up to the meter' is good, that leaves the meter, meter base and the feeder from it to the panel. There was a pic here a few days ago of a severely corroded meter base:

http://forums.mikeholt.com/showthread.php?t=186612
 
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