Solve This Service Call

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gar

Senior Member
210522-2016 EDT

A little more on magnetic sensing.

With my sensor and connected to a Fluke 27 I get about 0.1 to 0.2 millivolts as a residual background level. I have no filtering or shielding on the sensor.

With my 12 A load on a circuit I read a maximum of 0.5 to 0.6 millivolts from that load. Removing the load but keeping the sensor in the same location and orientation as when the load current was on the meter reading drops back to the 0.2 level. Thus, I am not seeing any substantial capacitive coupling from the 120 V Romex to my magnetic sensor. Thus, a real signal from the current in the Romex is present in my meter reading.

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ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
This is a WORTHLESS thread! It is of ZERO value to anyone.
Noticing more of this forum doing the same, albeit not necessarily 480's fault.

Used to look forward to reading this trade forum, because the remarks were interesting and thoughtful, and my contribution efforts did not seem pointless.

More frequently now, I'm looking for ways to unsubscribe from the kindergarten banter between social-media trolls, bickering, & antagonistic Tweets.
 

paulengr

Senior Member
Based on description sounds like a dead short or bad breaker. Apparently existing construction so first thing is assume it’s a load and remove them all. No loads so either it’s a bad recep or breaker. Visually inspect breaker and disconnect load wire. If it looks bad or still trips with wire removed, replace. Otherwise at this point Megger or ohm hot to neutral and ground. Based on detecting a dead short start disconnecting receptacles or taking covers off and narrow down the fault. You could also just take covers off and look.
 

n1ist

Senior Member
Location
Massachusetts
Occupation
Sr. Electrical Engineer
I would check outlet 6 to see if it was new. I'm guessing a split outlet that got replaced without breaking the tab.
 

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
I remember other "STSC" threads that brought criticism similar to several posts in this thread, and wonder if those who don't like this kind of thread might just stop reading, leaving it for those of us or are interested?

@480sparky
 

gar

Senior Member
210523-1744 EDT

Continuing my magnetic sensor experiments.

Now I have added a 1 mfd shunt capacitor in parallel with the magnetic sensor. Still no electrostatic shielding, still have the 12 A load current. Now my residual reading is around 0.01 to 0.02 millivolts. And my signal from the 12 A current is around 0.5 millivolts. Moving to a separate part of the same AC circuit, but where no current is flowing, the reading goes down to the residual level of 10 to 20 microvolts.

If the sensor is moved around the voltage will go up a little from an induced voltage from the earth's magnetic field. It is raining outside presently so I won't look for an induced signal from the power lines.

This method can be an effective tracing technique even when the source and return wires are close. If the wires are separated, then you can get much better detection.

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kwired

Electron manager
Location
NE Nebraska
Presuming not using a meter just screwdrivers, pliers, and such I guess first thing I do is try to turn on the breaker. Presumably it must have "thrown sparks" or whatever customer called what happens here and then tripped again. Most likely will be assuming a short circuit/ground fault on the circuit. Some might take cover off panel and do some looking, I possibly would have started in what I assume to be about the middle of circuit and disconnect things there and then see if breaker will set or not. Then I know which way to work from there.

Recently had somewhat similar situation I found the problem without needing a meter. My sister asking questions about a range. started out they first wanting to replace range with one they bought (used) but had the wrong cord on it. They were tripping breaker with existing, but did not trip when it was unplugged. So of course first guess is something wrong with range itself. Before started to look into it she said she was using oven but something smelled like it was burning, then heard a pop and it lost power.

All I did was take back cover off and saw problem before I even set the cover down. Someone didn't tighten terminal very well on one the ungrounded supply conductors and melted down the terminal block until it got to a ground fault condition.

I jerry rigged it bypassing the terminal and wire nutting supply cord to outgoing conductor of the appliance. Was used appliance to begin with and not worth finding a new terminal block for it IMO. Plus she lives an hour and a half away from me and I wasn't coming back just for this.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
I remember other "STSC" threads that brought criticism similar to several posts in this thread, and wonder if those who don't like this kind of thread might just stop reading, leaving it for those of us or are interested?

Nothing wrong with them if done right and can be a lot of fun. But this one has about as much information as you would get from a customer over the phone.

-Hal
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
..I guess first thing I do is try to turn on the breaker. Presumably it must have "thrown sparks" or whatever..
If anyone says breaker throws sparks, I believe OSHA or NFPA 70E prohibits turning it back on in the faulted condition.

You should check if breaker is energized in the off position, and if so check for line-line potential between the other source.

If more than one fuse powers the same wire, find other fuse powering it, & cap off wire from highest Amp fuse.

When I cap off such a wire I also wrap white tape around it and label it "FAULTED"
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
If anyone says breaker throws sparks, I believe OSHA or NFPA 70E prohibits turning it back on in the faulted condition.

You should check if breaker is energized in the off position, and if so check for line-line potential between the other source.

If more than one fuse powers the same wire, find other fuse powering it, & cap off wire from highest Amp fuse.

When I cap off such a wire I also wrap white tape around it and label it "FAULTED"
Since when are you allowed to have two fuses power the same wire?
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
If client pays for further repairs, and offending junction is eventually found, I believe most OCP listings, except perhaps QO, prohibit re-using breakers that cleared faults.

If fault is removed the wires in faulted path should be megger tested before put back in service.
 

kwired

Electron manager
Location
NE Nebraska
Since when are you allowed to have two fuses power the same wire?
I believe he is referring to situation where you might have power coming from another fuse/breaker whether unintentional or even say a line to line load where the other device is simply the other side of the supply for this circuit.
 
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