Bad lighting circuit

[JoeNorm]

I just finished electrifying a shop building in which the wiring had been done by a non-professional and is already partially concealed.

The HO used to turn the overhead lights on by plugging in an extension cord that was wire-nutted to the two lighting home runs. The ceiling is at least 25feet tall.

After hooking everything the breaker would trip on one of the lighting circuits. I looked at the rats nest I had cut apart and noticed he one of the GEC's had never been wired in(presumably because it would trip the breaker).

So there appears to be a ground-fault somewhere on that circuit. I have a few questions as I am not an experiences troubleshooter.

Is using continuity a reliable method for tracking down a fault? I get continuity between hot-ground right now but I am wondering if there are times where that can be a trick?

The circuit goes up the wall and to the ceiling where there are receptacles that the florescent lights plug. Is it more likely a fault be in the home run or in one of the lighting assembles. No way to know?

My thought was to find home run as far up the wall(still open framing with insulation) as reasonable and cut it, then see which half still has continuity.

Is there a better method?

 

[Dsg319]

I just finished electrifying a shop building in which the wiring had been done by a non-professional and is already partially concealed.

The HO used to turn the overhead lights on by plugging in an extension cord that was wire-nutted to the two lighting home runs. The ceiling is at least 25feet tall.

After hooking everything the breaker would trip on one of the lighting circuits. I looked at the rats nest I had cut apart and noticed he one of the GEC's had never been wired in(presumably because it would trip the breaker).

So there appears to be a ground-fault somewhere on that circuit. I have a few questions as I am not an experiences troubleshooter.

Is using continuity a reliable method for tracking down a fault? I get continuity between hot-ground right now but I am wondering if there are times where that can be a trick?

The circuit goes up the wall and to the ceiling where there are receptacles that the florescent lights plug. Is it more likely a fault be in the home run or in one of the lighting assembles. No way to know?

My thought was to find home run as far up the wall(still open framing with insulation) as reasonable and cut it, then see which half still has continuity.

Is there a better method?

I do that fairly often. Make sure the circuit conductors are not terminated in the panel “isolated” check for continuity from hot to EGC. Or which ever I am looking for.

 

[LarryFine]

If I may recommend a method for short circuit troubleshooting:

When troubleshooting a circuit with a direct short circuit to either neutral or ground, it's difficult to find the fault because you can't keep the power on, so the only way to find the offending undesired connection is visually, box by box.

I typically use a rubber socket with a 150-watt bulb screwed into it, and wire it in series with the problem circuit at the panel. I disconnect the circuit's hot wire from the breaker terminal, connect the socket's black wire to the breaker, and wire-nut the circuit's hot wire to the socket's white wire.


With the high-wattage bulb in series with the circuit, the breaker will stay on because the most current that can flow is that of the bulb, so it acts as a current limiter. It also functions as an indicator, steady bright for a direct short, flickering for an arcing fault, etc., with you or a helper watching it.

Alternately, if you're alone and distant from the panel, you can use a receptacle with an extension cord plugged into it to be able to keep the light (or any lamp) within sight as you troubleshoot, starting with wiggling receptacles, etc., depending on the type of circuit with the short.

In a pinch, you can use almost any load, like a vacuum or other noise-producing device, as an indicator. However, it is important to use a relatively high-current device, because you want it to have a lower impedance than anything you might have missed when unplugging stuff.

A few years ago, I had a troubleshoot for an intermittent short in a house old enough to have rigid conduit in the basement ceiling. I connected my bulb and socket as above, and it flickered, mostly bright. I traced the basement ceiling conduit to a J-box, and separated the outgoing hots.

One at a time, I reconnected each hot until one produced the same flickering. I then traced that line to a wire going up through the floor near the front door. I went to the foyer and found a surface-mounted Wiremold box with a cat-urine-soaked receptacle that was actually glowing internally.

 

[kwired]

I just finished electrifying a shop building in which the wiring had been done by a non-professional and is already partially concealed.

The HO used to turn the overhead lights on by plugging in an extension cord that was wire-nutted to the two lighting home runs. The ceiling is at least 25feet tall.

After hooking everything the breaker would trip on one of the lighting circuits. I looked at the rats nest I had cut apart and noticed he one of the GEC's had never been wired in(presumably because it would trip the breaker).

So there appears to be a ground-fault somewhere on that circuit. I have a few questions as I am not an experiences troubleshooter.

Is using continuity a reliable method for tracking down a fault? I get continuity between hot-ground right now but I am wondering if there are times where that can be a trick?

The circuit goes up the wall and to the ceiling where there are receptacles that the florescent lights plug. Is it more likely a fault be in the home run or in one of the lighting assembles. No way to know?

My thought was to find home run as far up the wall(still open framing with insulation) as reasonable and cut it, then see which half still has continuity.

Is there a better method?

Take apart at first possible place it is accessible, say first luminaire maybe? Then check to see which side of where you took it apart still has continuity and then you know which direction you need to be going to find the problem.

Could be nail or screw into cable somewhere, could be wire pinched when installing a box cover or portion of a luminaire or similar.

 

[Little Bill]

Continuity checks can be tricky, especially between hot/neutral or hot/gnd, since you may be reading through a load such as a light bulb. You need to make sure all loads are disconnected, meaning bulbs removed, cords unplugged, etc. before relying on a continuity check.

 

[JoeNorm]

Continuity checks can be tricky, especially between hot/neutral or hot/gnd, since you may be reading through a load such as a light bulb. You need to make sure all loads are disconnected, meaning bulbs removed, cords unplugged, etc. before relying on a continuity check.

Thanks, this is what I was not sure of but was wondering about. Unfortunately in this case I need a lift or scaffolding to unplug the lights!

 

[JoeNorm]

If I may recommend a method for short circuit troubleshooting:

When troubleshooting a circuit with a direct short circuit to either neutral or ground, it's difficult to find the fault because you can't keep the power on, so the only way to find the offending undesired connection is visually, box by box.

I typically use a rubber socket with a 150-watt bulb screwed into it, and wire it in series with the problem circuit at the panel. I disconnect the circuit's hot wire from the breaker terminal, connect the socket's black wire to the breaker, and wire-nut the circuit's hot wire to the socket's white wire.


With the high-wattage bulb in series with the circuit, the breaker will stay on because the most current that can flow is that of the bulb, so it acts as a current limiter. It also functions as an indicator, steady bright for a direct short, flickering for an arcing fault, etc., with you or a helper watching it.

Alternately, if you're alone and distant from the panel, you can use a receptacle with an extension cord plugged into it to be able to keep the light (or any lamp) within sight as you troubleshoot, starting with wiggling receptacles, etc., depending on the type of circuit with the short.

In a pinch, you can use almost any load, like a vacuum or other noise-producing device, as an indicator. However, it is important to use a relatively high-current device, because you want it to have a lower impedance than anything you might have missed when unplugging stuff.

A few years ago, I had a troubleshoot for an intermittent short in a house old enough to have rigid conduit in the basement ceiling. I connected my bulb and socket as above, and it flickered, mostly bright. I traced the basement ceiling conduit to a J-box, and separated the outgoing hots.

One at a time, I reconnected each hot until one produced the same flickering. I then traced that line to a wire going up through the floor near the front door. I went to the foyer and found a surface-mounted Wiremold box with a cat-urine-soaked receptacle that was actually glowing internally.

Thank you for the detailed description of this method. I need to re-read a few times.

 

[kwired]

Continuity checks can be tricky, especially between hot/neutral or hot/gnd, since you may be reading through a load such as a light bulb. You need to make sure all loads are disconnected, meaning bulbs removed, cords unplugged, etc. before relying on a continuity check.

Disconnect either (or both) EGC and neutral at the panel then if you have continuity between them it is still a condition that shouldn't be there.

If a place that has lots of metal, whether it be raceways, piping, structural metal best to isolate neutral as you may have multiple paths connected intentional or not to the EGC.