disappearing voltage once load is connected

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jmattero

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Hello:
I need some help from some of your pro's. I have a problem at one of my rental properties, in that I have an open neutral that I am trying to trace. In trying to trace it, I came upon a problem I have no idea on how to solve.

In any case, the tenant reports that the two switches that run the two lights in the kitchen do not work (all of a sudden, after working fine for the last five years). I tried to find this for two days, and I brought in an electrician today, since I could not find the problem.

Currently, the hot that feeds the two kitchen switches (both are single pole), and the neutral at that point read 118.5 volts. However, once a load is connected to this hot and neutral, the voltage drops to almost zero. I have taken the switches out of the equation, and connected a pigtail light across the hot and neutral, and the light does not go on.

In other words, the circuit appears fine as long as there is no load across it, However, once a load is connected, the voltage disappears. Both I and my electrician (who is a union electrician and also an electrical engineer) are baffled as to what could be causing this.

Does anyone have any ideas?
 
jmattero said:
.............Does anyone have any ideas?
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Try using a meter other than a digital one.

I'd say you've got a poor connection in the circuit, and the low impedence of a digital meter will show correct voltage, but put a load on the circuit and there's literally no connection somewhere. The connection is poor, but still has enough to let a trickle through that the meter picks up.
 
Ohms Law tells you whats wrong - there is a high supply impedence.

Given it looks like you're testing with a DVM, it is possible you are just reading capacitively coupled voltage and there is no actual conductivity at all to the supply. Which could be as simple as an open breaker, burned out or fallen off termination, etc...
 
How to test the neutral independant of the hot

How to test the neutral independant of the hot

In thinking some more about my problem... My problem is in circuit #2. Since I am not sure whether the problem is in the hot or in the neutral on Circuit 2, can I check this neutral by running an entension cord from a different circuit (Call this circuit #4) and connecting a load across the hot from circuit 4 and the neutral from circuit 2? It seems to me that would tell me whether the neutral for circuit 2 is good at that point (in the switch box for circuit 2). If that tests good, then it would seem to me that I have to look at the supply side of the circuit, rather than the neutral side. Any thoughts? Am I thinking correctly?
 
jmattero said:
... Any thoughts? Am I thinking correctly?
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The test procedure you propose will likely provide some insight... but it may prove to be damaging and is definitely an unsafe procedure.

This troubleshooting is not rocket science. Simply isolate at junctions your line and load conductors (with breaker turned off then reenergize once isolated), and test the line with a [light] load. If the no/low voltage condition exists at that junction, move one or more junctions closer to the source to pinpoint the fault. When a junction tests good, reconnect solidly while deenergized and move to the next one away from the source. Test the easiest accessible junctions first.

PS: Testing may prove the fault is not at a junction, but rather in the cable between junctions.
 
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jmattero said:
my electrician (who is a union electrician and also an electrical engineer)
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An Electrical Engineer who is also a Journeyman Electrician should be the smartest guy in the world but even he is totally confounded by a 15 amp 120 volt branch circuit!

Man I love this trade! :)
 
N844AA said:
An Electrical Engineer who is also a Journeyman Electrician should be the smartest guy in the world but even he is totally confounded by a 15 amp 120 volt branch circuit!

Man I love this trade! :)
Click to expand...

Believe me, if you were dealing with the engineer(s) I'm dealing with on one of my current projects you would swear they were the dumbest creatures alive.

This is no indication of my overall veiw or respect of engineers, it is isolated to this particular bunch I'm having to deal with at the moment. :grin:

Roger
 
100224-1954 EST

jmattero:

The problem you have is one that is easy to determine whether the problem is the hot or neutral. You have to have a fundamental understanding of circuits. It helps to draw it on a piece of paper and jot down the voltage differences at different points under different conditions.

It could be both. But once you know which one or both, then start from the source.

At this time I will not provide you with any direct suggestions on how to do this troubleshooting.

Find yourself an electrician that is capable of troubleshooting. I doubt the referenced electrical engineer was a real engineer.

.
 
Is that the only thing not working?
Test the plugs in the area so you know what works, then turn off all breakers except the one that gives you power at the switch. Test to see what is still on, in a line from the panel, short and straight is mostly how stuff is ruffed in, go to the nearest still working opening to the switch see if the wire fell out of the back of the device or any other problem.
Could even be a broken wire in a wirenut that finally gave up too.
 
roger said:
Believe me, if you were dealing with the engineer(s) I'm dealing with on one of my current projects you would swear they were the dumbest creatures alive.

This is no indication of my overall veiw or respect of engineers, it is isolated to this particular bunch I'm having to deal with at the moment. :grin:

Roger
Click to expand...

Believe me, if you were dealing with the electricians(s) I'm dealing with on one of my current projects you would swear they were the dumbest creatures alive.

This is no indication of my overall view or respect of electricians, it is isolated to this particular bunch I'm having to deal with at the moment.
 
weressl said:
Believe me, if you were dealing with the electricians(s) I'm dealing with on one of my current projects you would swear they were the dumbest creatures alive.

This is no indication of my overall view or respect of electricians, it is isolated to this particular bunch I'm having to deal with at the moment.
Click to expand...

What a coincidence, I bet they came from the same multi tasking engineering company. ;)

Roger
 
Hehehehe, not easy on the eyes either. brian john says he wouldn't hire me ;-) I guess the bad looking's opinion doesn't count as relevant ;-))))))))
 
check for backstabbed receptacles with burned neutrals. if you have 120v on both wires to ground and 0 hot to neutral with the switch on i am assuming you possibly have a burned neutral somewhere. i dont know for sure without being there
 
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