Solve This Service Call

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Clayton79

Member
Location
illinois
Fwiw – I appreciated the intent of this post. Yes, of course, the first details were on the thin side, but those few details reflect exactly what 480 initially saw when walking into this murder mystery troubleshooting call. So the “game” is to start asking questions and see if your first inclinations about what to eyeball might have panned out and how close they came to his first efforts at troubleshooting this. Just a fun exercise and, in the end, always some good facts to put onto your “been there, saw that” list. Complaining about the game seems silly and grumpy to me, have fun and play along. Or simply pull up a chair on the sidelines and watch, and keep the heckling to a dull roar

Moral of this troubleshooting story – Lady Penelope would be alive today – and collecting fat alimony checks - if these were pigtailed outlets.
Too long to quote all of it but
Best post I have seen in ..maybe forever
 

Clayton79

Member
Location
illinois
After determining which circuits were off, I would’ve asked receptionist if anything had been plugged in at all to either of those outlets when the situation happened I would’ve checked it out first and I would have looked for any obvious signs of charring or smell any burnt smells I would have used meter to check for direct short, and looked for first receptacle in chain, to break and recheck feed from breaker and down the line for shorted hot to neutral/ground
 

Clayton79

Member
Location
illinois
It’s a troubleshooting/teaching thread and it could be a lot of a lot of value to those who don’t get to do much of it if all of our geniuses would play along
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Taking off from Larry Fines excellent start (collected together in the Quotes in Post # 39, above), I will guess that the voltage test on the breaker load terminal is zero volts when the breaker is turned OFF.
1. Remove the branch circuit conductor from the breaker load terminal; turn the breaker on and see if it holds. If the breaker holds, and there is now nominal voltage on the load terminal, the breaker is almost certainly OK.
2. Turn breaker OFF and reconnect the branch circuit conductor.
3. Given that the panel is in the basement, to the extent practical, examine the path of the Home Run that lands at the tripping breaker, paying attention to any visible J-boxes.
4. A plug-in circuit tester shows that only receptacles 1 thru 5 have no power ( see 480 Sparky's Post # 24).
5. The basic idea now is, after having visually cataloged probable conductor splice locations, start by opening Outlet # 1 (it is closest to the panel) and look for feed-thru splices. Finding them, separate the energized conductors and try turning the breaker back on. This is the first attempt to isolate a portion of the circuit that is good, from the faulted portion.
6. If the breaker holds, that means the portion still OFF (presumably Outlets #2 - 5) is where the fault is. Turn the Breaker OFF.
7. Restore the splice of the Energized conductors in Outlet # 1. Divide the remaining run of the Branch Circuit at, say, Outlet # 4, turn the breaker back ON and see if it holds.
8. Repeat as necessary.
9. Keep in mind to visually inspect for burn marks, exposed conductors in contact, or other problems while disassembling the Outlet or Junction Box.
 

gar

Senior Member
210521-1233 EDT

The title of this thread is "Solve This Service Call", then in the first post
"I didn't use any high-$ tools.... just what I have in my tool tote. Screwdrivers, linesmans, strippers etc."

The title implies getting to the actual cause of the problem. Not just how to start troubleshooting.

Relative to tools the information seems to imply no meters.
Quite possibly critical to the problem is the statement ---
" Breaker "tosses sparks and won't stay on"."

Quite possibly means an inductive load.

I ran some trip times on some breakers about 60 years ago. This included a QO, and some other breakers. The QO was with a cover removed so I could place probes internal to get timing information. When a QO opens it produces a fairly large air gap between the contacts. Quick quenching of an arc. My power source to trip this breaker was 6 or 8 car batteries in series, very little wire length of about 0000 size, and a homemade shunt across the output. By memory I was somewhat above 6000 A peak current. I don't remember any "tossing sparks". I had no appreciable inductance in the circuit, just wiring inductance. Wires were quite short.

I think a more appropriate title would have been "How would you approach this service call". Then at the start of the description list the tools available to use. Define the breakers involved.

The statement of the problem seems to imply a short circuit load on that breaker.

So one would start by disconnecting the circuit at the breaker. Does the breaker now hold? If not, then then one has to look around the breaker for a short. Not likely to find one for a QO breaker. The basic design of a QO sort of makes it impossible to have an output short on the breaker with the load wire removed.

Assuming the breaker looks good from the above experiment, then you might connect a 100 W incandescent between the breaker output and the breakers load circuit. Full brightness is expected. With no instrumentation available you need to break the load circuit at various places to isolate where the short is located.

I would say that virtually all the responses to this thread are good, and that between the title of the thread, and the first post that the implications, and given information were inadequate.

Now I have a question for all of you, nothing to do with this thread in particular, other than to make you think. What is the maximum phase shift of a resistor capacitor network?

.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I was only trying to point out that the OP had the advantage of actually walking in and looking at the situation. He already was one step ahead. All I was after was what he observed when he was there, not what he did. If the info was given up front of JUST WHAT HE SAW, then we could have given steps we thought were appropriate. Also, it is very possible and probable that he had already asked some questions over the phone and kind of knew a direction to go.

It would have been a very simple thing to do to just say:
"I received a call about breaker tripping and sparks flying
I go there and was shown the diagram of the outlets, the actual outlets, and directions to the panel
Of the 6 outlets, only 5 were not working and the breaker was off (not sure if it was off or tripped)
What would be your troubleshooting steps to find the problem?"

Instead, all we got was "solve this service call"!
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
All I was after was what he observed when he was there, not what he did. If the info was given up front of JUST WHAT HE SAW, then we could have given steps we thought were appropriate. Also, it is very possible and probable that he had already asked some questions over the phone and kind of knew a direction to go.

I wish troubleshooting worked that way . . . when the call from the client for service comes in, my Augmented Reality Communicator streams an A.I. assembled feed from the client's always-on head-worn cameras that shows what I will see when I get there.

But the reality is that I walk into the door COLD and start the decision tree of Heuristic Logic. I have already taken the trouble call, and know that I can't diagnose sight-unseen over-the-phone and I have already told the client I have to be on site to troubleshoot. The first thing I do when I walk in the door is already the "Troubleshooting Process"

480 (Ken) is accurately asking: "What is your troubleshooting process."
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I wish troubleshooting worked that way . . . when the call from the client for service comes in, my Augmented Reality Communicator streams an A.I. assembled feed from the client's always-on head-worn cameras that shows what I will see when I get there.

But the reality is that I walk into the door COLD and start the decision tree of Heuristic Logic. I have already taken the trouble call, and know that I can't diagnose sight-unseen over-the-phone and I have already told the client I have to be on site to troubleshoot. The first thing I do when I walk in the door is already the "Troubleshooting Process"

480 (Ken) is accurately asking: "What is your troubleshooting process."
Except that is not what he asked. He asked (per the title) "solve this service call"
 

oldsparky52

Senior Member
I guess no one understands the concept of teaching.

I'm done here. Have fun.
My guess is you are one of the "no one"s.

If you really just wanted to teach, you could have told us step by step how you found what must be a very unusual problem (or you wouldn't be telling us about it). There is probably a good story and good teaching opportunity but we hurt your feelings so now you won't finish.

I'm sorry for my contributions to hurting you, would you please come back and tell us what you found and how you found it (teach us)?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have found that the vast majority of the time what people tell me is going on when something isn't working correctly isn't really what's happening. People tell you what they think is going on not what they actually see.

I have this happen a lot with control systems where I can go back and look at the alarm log and see what actually happened, so I am usually pretty suspicious that what someone tells me is going on is not really what's happening.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
1. Remove the branch circuit conductor from the breaker load terminal; turn the breaker on and see if it holds. If the breaker holds, and there is now nominal voltage on the load terminal, the breaker is almost certainly OK.
Is there value at this point to testing for continuity between the circuit ungrounded conductor at the panel and the grounded conductor bus? If there's continuity that tells you that either there's a short in the wiring, or you're measuring through a load. The latter, based on only 5 receptacles being out, with nothing plugged into them, is not expected, although still would be possible. I don't think there's a simple measurement you can make at the panel to distinguish between the two possible causes of continuity?

Cheers, Wayne
 

gar

Senior Member
210522-1407 EDT

Following are some techniques that can be used to troubleshot this kind of problem. These tests include items that the OP is unlikely to have had.

Equipment:
A good 3 1/2 digit meter like a Fluke 27.
A 1500 W space heater.
A long extension cord.
A magnetic field sensor.

Place heater between breaker output and the circuit's hot wire that was removed from the breaker. We will assume there is a short somewhere out in said circuit. We will assume equal size wire and material for the circuit wiring. If there is a really good short, then current in a 120 V circuit will be about 12 A from a 1500 W heater, and the heater on in it's full heat position. If the EGC is good, and no extraneous signals are present, then this can be used as a meter lead back to neutral at the main panel.

With equal wires for the hot and low side (neutral, except it really is not a neutral), then voltage drop along the circuit is uniform per unit length. The point of the short will be 1/2 the voltage into the circuit.

If the EGC does not make a good test lead to the main panel, then use an extension cord as a test lead.

Search for the 1/2 voltage point. Note, #12 copper wire is about 1.59 ohms per 1000 ft. Thus, 100 ft formed into a 50 ft loop is 0.159 ohms. At 12 A this equals 1.9 V across the loop or 0.95 V to the point of the short. Any points beyond the short will have the same voltage as at the point of the short.

Assume no loads on the circuit except a single short somewhere. Suppose you do not have a very low resistance short, then as you make measurements along the circuit path you will get lower voltage readings on the hot wire as you progress from the main panel to the point of the short, then beyond the short point the voltage remains at the same value as at the short point. If you measure the voltage on the low voltage side of the path, then the voltage increases toward the short point. In this case there is some substantial voltages across the shorting element.

I can also search for a stray magnetic field from the two conductor cable up to the point of the short. But this can be hard to detect because of distance from the cable. This also has the problem of the orientation of the two conducting wires in the cable relative to where I can place the magnetic sensor.

With magnetic sensor experiments I just ran it is possible to see the Romex cable in the wall from a 1500 W heater load. These are 2 x 4 walls with plaster board, and plaster covering the 2 x 4 s. The signal I get is small, but observable. The experiment would be much better at 100 A. If the load was short 100 A pulses that would not trip my 20 A breakers, and using short pulses with adequate off time won't overheat the wiring. Orientation of the two wires in the Romex cable relative to the magnetic sensor has a substantial effect on signal level.

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