Residential troubleshoot

[growler]

I would ask the home owners if they were adding/doing anything or having anything done by someone else at the same time they lost power to the lighting circuit.

Sure, I always ask the same questions. Get as much information as possible.

 

[kwired]

Did you open/separate the EGCs in that box ? Wherever your hot is shorted, it could be returning on the other circuits ground.

Not yet. That's the next step.

You mentioned you did pull those switches out (I think) Was all the EGC's tied together, supposedly they should be, I will admit to not always doing that though. if not and you did pull switches out you possibly did eliminate possible casual contact across circuits while you had the pulled out.

If you have a general idea of how the circuit may be run behind walls, ceilings, etc. go to a box somewhere about middle of circuit and disconnect things - and take measurements/run your vacuum test again. This will narrow things down to which half of the circuit you need to focus on. Possibly halve it again in similar manner.

Read how to do that in my Electricians Handbook while still in school and a set of test lights were the norm. Used it within weeks and got a pat on the back from the Journeyman I was working with.

The amp meter to find the return path is a good hint. We were working in a packed tight panel a couple weeks ago that I used a thermal imaging camera to find which was the neutral of a MWBC by scanning the neutral terminations. Got me down to choice of two that were laying closely together.

Was easiest to use a test lamp with old Edison fuse panels you just screw the lamp directly into fuse holder.

 

[GoldDigger]

Yeah, if you have an idea of how the branch circuit was installed.
Logic would dictate start at outlet boxes closest to the source, panel, and start there isolating the hot conductor from down stream.


I looked at my fiend and I said I bet we drove a nail into the wiring. Like I said it was a good thing his wife was home. We only had to pull a couple of nails to clear the fault.

1. Your fiend? Is that a Freudian slip? (When you say one thing but mean your mother.)
2. I hope you did not just leave the damaged wire after pulling the nail.


Sent from my XT1585 using Tapatalk

 

[LarryFine]

Didn't get there today, but we did get today's work done, so we'll get there tomorrow.

Yes, I asked many questions before I started doing the exploratory surgery Saturday.

Thanks for the suggestions and thoughts. I'll let you know what we find out tomorrow.

 

[ggratecc]

I realize you tried turning all the light switches OFF but short persists.
I would remove all light bulbs from their socket.
Also, could there be a security light (non-switched) that could be the cause?
How about a t-stat controlled attic fan?

Obviously, isolating the circuit run in half and troubleshooting is most logical way.

 

[gar]

180220-2209 EST

Suggestions to use an Amprobe are good and useful.

I think trial and error of taking things apart is a slow way to find the problem. But that is what many of the suggestions are.

Back to my stray magnetic field method.

I have an extension cord from my main panel to one of my work benches. This gives test probe wires from the main to my bench. This cord is from possibly 1 ft to a number of feet from from the power cable to my bench. Thus, I can generate stray magnetic fields using these wires to produce an open loop. Neutral is from my bench supply and the 1500 W heater is from bench neutral to the 120 V hot in the extension cord. Several feet from this open loop I can see a millivolt or more of induced voltage inro the test coil from the 10 A loop current.

Orientation of the test coil is important to sense the stray field. This also gives you information where the current is located.

When you go past the point of the short the induced voltage will drop to the background level. This stray field is going to go thru most walls.

To reduce unwanted signals I placed 2 ufd in parallel with the coil.

.

 

[LarryFine]

Without responding to individual posts, here's the update:

Today, using my clamp-on ammeter, I found two EGCs that equally shared the vacuum's current, both from circuits that share boxes with the offending circuit. One was the 2-g box coming into the kitchen from the garage, which has lighting on a separate circuit, and one from the disposer/dishwasher MWBC, where the disposer switch shares the 2-g bpx with the over-the-sink light switch.

I opened both boxes and separated every EGC in each box. That affected the vacuum, so I took it back out of the circuit and reconnected the problem circuit's black back to the breaker (as well as the neutral and EGC), which allowed the lighting to come on. Then, with my solenoid tester, found one hot EGC in each box (telling me the two were still connected in another box) against the neutral.

That pointed me to the rest of the switch boxes on the circuit, including another 2-g box with the kitchen light's other 3-way (the first at the garage door) as well as a dimmer controlling the dining-room light, which did not turn on. I found the right EGC to disconnect, which stopped the solenoid tester from indicating the hot EGC. Ready for this? The wire I disconnected was from the dimmer itself.

Apparently the triac was internally shorted to its normally-isolated mounting tab, which is riveted to the dimmer's metal front plate for heat-sinking. I confirmed by reconnecting all of the EGC's, and testing between the dimmer's green wire and the box's EGCs. The solenoid tester indicated a full 120 volts. Replaced with a switch, everything was back to normal and the customers were happy.

 

[Jamesco]

Without responding to individual posts, here's the update:

Today, using my clamp-on ammeter, I found two EGCs that equally shared the vacuum's current, both from circuits that share boxes with the offending circuit. One was the 2-g box coming into the kitchen from the garage, which has lighting on a separate circuit, and one from the disposer/dishwasher MWBC, where the disposer switch shares the 2-g bpx with the over-the-sink light switch.

I opened both boxes and separated every EGC in each box. That affected the vacuum, so I took it back out of the circuit and reconnected the problem circuit's black back to the breaker (as well as the neutral and EGC), which allowed the lighting to come on. Then, with my solenoid tester, found one hot EGC in each box (telling me the two were still connected in another box) against the neutral.

That pointed me to the rest of the switch boxes on the circuit, including another 2-g box with the kitchen light's other 3-way (the first at the garage door) as well as a dimmer controlling the dining-room light, which did not turn on. I found the right EGC to disconnect, which stopped the solenoid tester from indicating the hot EGC. Ready for this? The wire I disconnected was from the dimmer itself.

Apparently the triac was internally shorted to its normally-isolated mounting tab, which is riveted to the dimmer's metal front plate for heat-sinking. I confirmed by reconnecting all of the EGC's, and testing between the dimmer's green wire and the box's EGCs. The solenoid tester indicated a full 120 volts. Replaced with a switch, everything was back to normal and the customers were happy.

Dimmer? I don't recall you saying anything about a dimmer on the faulted circuit. Heck, that is first place I would have checked, LOL. I bet you were relieved when you finally found the problem.

Those dimmers can cause all kinds of problems. As you probably already know if a customer calls you saying they have a breaker that trips every once and awhile for no apparent reason and the breaker is an AFCI, one of the first places to look, is for a dimmer/s on the circuit that use the neutral conductor.


.

 

[Little Bill]

Good job Larry!

I see you got the PM I sent telling you where to look!:angel:

 

[ptonsparky]

How come the problem is always in "the last place"?

 

[Little Bill]

How come the problem is always in "the last place"?

That's where I always find my keys!

 

[growler]

I think trial and error of taking things apart is a slow way to find the problem.

Trial and error would be a slow way to find the problem. What was suggested was that he try to isolate the problem by dividing the circuit in half and then maybe in half again.

If you divide a circuit in half and find that the shorted section is not in the home run or the first half of the circuit there is really no reason to even take the cover off the panel.

If you do find the shorted section of wiring is in the home run or first half of the circuit at least you are not running over the rest of the house looking for a problem. The idea is to keep the area you need to troubleshoot as small as possible.

 

[al hildenbrand]

. . . Ready for this? The wire I disconnected was from the dimmer itself.

:thumbsup:

Great troubleshoot ! !

Thanks for the story of it.

 

[kwired]

Dimmer? I don't recall you saying anything about a dimmer on the faulted circuit. Heck, that is first place I would have checked, LOL. I bet you were relieved when you finally found the problem.

Those dimmers can cause all kinds of problems. As you probably already know if a customer calls you saying they have a breaker that trips every once and awhile for no apparent reason and the breaker is an AFCI, one of the first places to look, is for a dimmer/s on the circuit that use the neutral conductor.


.

Didn't really matter that it was a dimmer that faulted. The thing that did complicate the troubleshooting process was that the EGC was interconnected with another path (EGC of other circuits). Not that this was wrong, but did lead him somewhat astray in the troubleshooting process. Any other faulted item in same circuit would have done about the same thing.

 

[growler]

Didn't really matter that it was a dimmer that faulted. The thing that did complicate the troubleshooting process was that the EGC was interconnected with another path (EGC of other circuits). Not that this was wrong, but did lead him somewhat astray in the troubleshooting process. Any other faulted item in same circuit would have done about the same thing.

It's hard to find a house where there won't be EGCs tied togather. If there is more than one circuit in the junction box the ECGs normally will get tied togather.

What I still don't know is if the triac was shorted to frame was it only shorted with power on or all the time?

If it was shorted all the time (even with power off) then why not just use a meter to a known good ground to determine which section of wiring was bad. If I know I have a hot to ground short then I normally wouldn't troubleshoot with power on.

 

[kwired]

It's hard to find a house where there won't be EGCs tied togather. If there is more than one circuit in the junction box the ECGs normally will get tied togather.

What I still don't know is if the triac was shorted to frame was it only shorted with power on or all the time?

If it was shorted all the time (even with power off) then why not just use a meter to a known good ground to determine which section of wiring was bad. If I know I have a hot to ground short then I normally wouldn't troubleshoot with power on.

Quite often in a dwelling you can get away with assuming there is no other EGC path. That was Larry's main mistake here. Had he had similar problem in a building with metal raceways and steel structural components - he would have had all sorts of potential return paths.

 

[LarryFine]

Dimmer? I don't recall you saying anything about a dimmer on the faulted circuit. Heck, that is first place I would have checked, LOL. I bet you were relieved when you finally found the problem.

It will be next time, and yes, us and the customer!

Those dimmers can cause all kinds of problems. As you probably already know if a customer calls you saying they have a breaker that trips every once and awhile for no apparent reason and the breaker is an AFCI, one of the first places to look, is for a dimmer/s on the circuit that use the neutral conductor.

A bolted fault, no AFCIs, the kitchen/foyer lighting circuit, 2-wire dimmer.

 

[LarryFine]

Good job Larry!

I see you got the PM I sent telling you where to look!:angel:

Um, no.

 

[LarryFine]

Quite often in a dwelling you can get away with assuming there is no other EGC path. That was Larry's main mistake here. Had he had similar problem in a building with metal raceways and steel structural components - he would have had all sorts of potential return paths.

Not a mistake, just a step-by-step process of elimination, leading to isolation of the fault location.

 

[gar]

180221-1030 EST

I believe my voltage measurement technique of main panel EGC bus to other points could have reduced the time and effort to find the shorting region.

Ran an experiment this morning with the following equipment:

1. A duplex outlet at the main panel (short leads) to EGC bus, neutral bus, and a lightly loaded 120 V breaker.

2. Two 3 conductor 50 ft extension cords in series from said main panel outlet for a long test lead, and laid out in any old way. I doubt that in my case there is any major induced voltage from stray magnetic fields into this random 1 turn coil open loop.

3. Fluke 27 on AC V range, not mV. Resolution 0.001 V ( 1 mV ). No bandwidth limiting other than Fluke 27 that is about 50 kHz. It would be useful to have a bandpass filter at 60 Hz.


Results:

EGC bus to neutral bus in main panel with standard Fluke leads --- 0.001 V, verified at 1 mV on the mV range.

My best reading within the house of a remote EGC to main panel at a point about 50 ft from main panel was 2 mV.

I have many 8' and 4' fluorescents in the house. Every fluorescent has a noise filter. The noise filter is pass thru for hot and neutral. Some of the filter capacitors go to EGC.

In some spots with some stuff on I saw upwards of 10 mV for remote EGC to main panel EGC. My Romex EGC wires are not full size ( 1965 Anaconda ).

All hot and neutral wires are #12 copper.

With a 10 A load on a neutral it is easy to see several hundred mV between the load point and the main panel.

In Larry's case I expect he would have seen several hundred mV on a front screw of the dimmer. This kind of test would have required no boxes to be opened to narrow down the shorting location.

This neutral voltage drop measurement technique can be used to determine the sequential ordering of outlets on a circuit.

,