Half circuits don't work

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ZtomvZ

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I am having a problem identifying a problem w/ a sub-panel in an apartment. Only half of the spaces in the bussing hold a 20 amp circuit. On the rest, when I put a load on them, it dosen't hold the load. A wiggie shows that there is power, but I plug in a light, it dosen't work. I checked the main feeder wires & they both have power to them. Any ideas?
 
You have a bad connection or a bad leg(phase). There may be enough connection to allow your tester to operate but with a load I bet the meter will read zero to ground. If that is the case look for a bad wire or bad breaker feeder the panel.
 
Sounds like you either lost a phase or are having some kind of neutral problem. Check phase to phase, Phase to ground, Phase to neutral, Ring continuity from neutral to ground first check voltage neutral to ground. Make sure there is a load on when testing these voltages.
 
quogueelectric said:
Sounds like you either lost a phase or are having some kind of neutral problem. Check phase to phase, Phase to ground, Phase to neutral, Ring continuity from neutral to ground first check voltage neutral to ground. Make sure there is a load on when testing these voltages.
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If it were a neutral problem then I don't think half the circuits would be working-- at least not properly. :D
 
I'd vote for losing on phase, or leg, of the service or feeder.

Identify which phase, and which lug feeds it. Start working back towards the service.

And, Welcome to the forums! :smile:
 
I plug in a light, it dosen't work

I plug in a light, it dosen't work

A Wiggie draws 5 mA. A lamp draws ~ an amp.
So, the upstream resistance (Thevenin equivalent) is <1000 ohms and >12 ohms. It should be <0.3 ohm or so.
It's not Romex stray capacitance between conductors, that's probably 100K ohms.

Could be a bad connection or small appliance in series with the line.
 
if half the panel works, you have a bad connection. trace the conductors bacvk to the main panel and i bet you will find either a bad connection on the breaker, a bad breaker or a problem with the bus its self. or maybe theres even a problem in the main panel that no one seemed to notice yet
 
Lxnxjxhx said:
A Wiggie draws 5 mA. A lamp draws ~ an amp.
So, the upstream resistance (Thevenin equivalent) is <1000 ohms and >12 ohms. It should be <0.3 ohm or so.
It's not Romex stray capacitance between conductors, that's probably 100K ohms.

Could be a bad connection or small appliance in series with the line.
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how do you know all this scientific stuff
 
As 480 mentioned you probably lost a phase.

There is a good chance your measuring voltage on the lost phase that is coming through a load downstream.

Open all the breakers or fuses and then check the incoming line for a lost phase.
 
bad disconnect sw

bad disconnect sw

We had a problem at our townhouse complex recently and it was a corroded disconnect switch that caused similar symptoms.
 
how do you know all this scientific stuff

how do you know all this scientific stuff

I was educated far beyond my intelligence, kind of like putting 10 gal. in a 1 gal. bucket.
 
corrosion vs. high resistance

corrosion vs. high resistance

corrosion.jpg


A scope across the resistive or reactive load impedance should show a waveform of less than 170v peak amplitude and it should look "somewhat rectified."
I assume the value of the "components" inside the corroded connection depend on current, temp., vibration, bolt torque, etc. I wouldn't use an incandescent lamp for the load .
 
Lxnxjxhx said:
A scope across the resistive or reactive load impedance should show a waveform of less than 170v peak amplitude and it should look "somewhat rectified."
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Glad were not trying to over think this problem.
 
over think

over think

Kinda' goes with the 10 gal./1 gal. stuff.
 
Re-torque the main lugs with a torque wrench to panel label specifications?

Oxidized aluminum wiring on main lugs because anti-oxidant goop was not applied at installation?
 
Dennis Alwon said:
If it were a neutral problem then I don't think half the circuits would be working-- at least not properly. :D
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First of all I will guarantee you that it its a phase loss problem. The point I am trying to make is to take all voltage readings at one time instead of going on a witch hunt. He probably lost 1 phase and is reading voltage through his 2 pole ckts. He will get 120v on both a and b phase until he shuts off all 2 pole breakers where he will read 0 volts on 1 leg and at no point will he get 240 anywhere. We are trying to learn to troubleshoot here I hope you learned something today as he was reading voltage through his 2 pole loads.
 
Another thing to try is to turn off the main breakers feeding the subpanel, then turn them back on (best to do with covers on of course).

Sometimes you have a 240V tie-bar breaker which is really two separate breakers connected together via the tie bar (and the tie bar has a lot of play in it). One breaker will trip, but the other will remain on. So you get one leg dead and the other leg with power remaining.
 
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