Solve This Service Call

480sparky

Senior Member
Location
Iowegia
Time to leave breaker #14 off, attach a voltmeter to the terminal, then start turning off breakers 3,4,7,8,11,12,15,16,19 and 20. Whichever one turns off power to the terminal is the 'other side' of the dead short.

Now what?
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Time to leave breaker #14 off, attach a voltmeter to the terminal, then start turning off breakers 3,4,7,8,11,12,15,16,19 and 20. Whichever one turns off power to the terminal is the 'other side' of the dead short.

Now what?
1. Identify which of the receptacles, lights, or other loads are being supplied when either the #14 or the other "fighting" breaker (call it #M) are turned on.
Turn off all these loads, and then use a clamp meter to measure any current from #14 when it's turned ON to make sure that it's very low. If you can't make it near zero then note down the amount of current.
2. Put a high wattage lamp as Larry said (or another substantial test load) from the conductor fed by the #M breaker to the neutral bar (obviously with #14 and #M turned off. Then measure the current from the #14 breaker when it's turned on.
3. Starting at what you think might be the middle of the run to the loads noted above, open a box and if it has a hot wire feeding thru the box (ie., not dead-ending), put a clamp meter on the hot wire, and then turn on #14 to see if the load current is present. If no current then the short between the two circuits must be closer to the breaker panel, and so move to a box closer to the panel and check again. If current is present then move further away from panel. Try to zero in on location of "dead short", looking closely where you see hots are tied together. They can then be disconnected to check if the test load is no longer being fed, and further tests depending on what is found.
 

480sparky

Senior Member
Location
Iowegia
1. Identify which of the receptacles, lights, or other loads are being supplied when either the #14 or the other "fighting" breaker (call it #M) are turned on.
Turn off all these loads, and then use a clamp meter to measure any current from #14 when it's turned ON to make sure that it's very low. If you can't make it near zero then note down the amount of current.
2. Put a high wattage lamp as Larry said (or another substantial test load) from the conductor fed by the #M breaker to the neutral bar (obviously with #14 and #M turned off. Then measure the current from the #14 breaker when it's turned on.
3. Starting at what you think might be the middle of the run to the loads noted above, open a box and if it has a hot wire feeding thru the box (ie., not dead-ending), put a clamp meter on the hot wire, and then turn on #14 to see if the load current is present. If no current then the short between the two circuits must be closer to the breaker panel, and so move to a box closer to the panel and check again. If current is present then move further away from panel. Try to zero in on location of "dead short", looking closely where you see hots are tied together. They can then be disconnected to check if the test load is no longer being fed, and further tests depending on what is found.
Let's back up a bit. We know at this point there's two circuits tied together somewhere. But before we start on a wild goose chase, let's try to narrow down our search.

Breaker #14, which is a 15a, has 122.4v at the terminal when turned off. This means there's another circuit back-feeding into the panel. If it was a circuit on the same leg, then it would stay on and no breakers, even the main, would trip. But since the main trips, that means the 'other' circuit is on the other leg.

This means circuits 3,4,7,8,11,12,15,16,29 and 20 are suspects.

So I just used my voltmeter hooked to breaker 14 and.............?
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Let's back up a bit. We know at this point there's two circuits tied together somewhere. But before we start on a wild goose chase, let's try to narrow down our search.

Breaker #14, which is a 15a, has 122.4v at the terminal when turned off. This means there's another circuit back-feeding into the panel. If it was a circuit on the same leg, then it would stay on and no breakers, even the main, would trip. But since the main trips, that means the 'other' circuit is on the other leg.

This means circuits 3,4,7,8,11,12,15,16,29 and 20 are suspects.

So I just used my voltmeter hooked to breaker 14 and.............?
You measured 122.4V from the #14 breaker terminal to neutral when the breaker is turned off, so it's being back-fed by one of the phases. To determine which phase, measure the voltage at the turned off #14 breaker terminal relative to the busbar that feeds the #14 breaker (or relative to other "turned on" breaker outputs from that busbar). If you see about 240V then that confirms that the "other" circuit is on the opposite leg.
 
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LarryFine

Master Electrician Electric Contractor Richmond VA
2. Put a high wattage lamp as Larry said (or another substantial test load) from the conductor fed by the #M breaker to the neutral bar (obviously with #14 and #M turned off.
I meant in series with the circuit line conductor. In other words, take wire off breaker, wire-nut it to one socket wire, put other socket wire on breaker.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I meant in series with the circuit line conductor. In other words, take wire off breaker, wire-nut it to one socket wire, put other socket wire on breaker.
I understood your post about putting it in series, but 480sparky's posts led me to believe that doing this might put 240V across the lamp if the breaker is turned ON. Hence my comment about putting the lamp between the line conductor on the breaker and neutral (i.e, about 120V), which should provide a test current through both of the circuits that are improperly tied together.
 

480sparky

Senior Member
Location
Iowegia
OK, let's explain where we are at this point.

There's a short between circuit 14 and a circuit on the other leg. This is shown by 120v at the breaker terminal when it's off. So a voltmeter is connected to the terminal and the neutral.

Now think about this. You have a meter that shows 120 volts. Right in the panel full of the other circuits and breakers that are capable of turning off those circuits.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Turn off EVERY breaker on the opposite leg of #14 (the ones you listed) with your meter on #14 and neutral, start turning on each of the turned off breakers until you find the one that's causing the voltage on #14. Find what this new found breaker operates. Start disconnecting boxes and check the hots. You could go and turn on each of the two breakers, one at a time and check for voltage on each of the disconnected wires. If you find two wires that were connected together and both show voltage when taken apart, you have found your double or back feed.
My guess would be in a switch box with more than one feed in.

ETA: You could also turn one of the two breakers on and see what's working. Then turn that one off and the other on and see if there any different things working or not working.
 

480sparky

Senior Member
Location
Iowegia
So cycling breakers 3,4,7,8,11,12,15,16,19 and 20 shows that turning off 11 turns off power to the terminal of breaker 14.

This means breakers 11 and 14 are tied together somewhere. But instead of opening boxes, I just read the panel directory.

14, as stated was "Kitchen hall bath basement lights". 11 is marked "Kitchen outlets".
 

480sparky

Senior Member
Location
Iowegia
Where were they joined at? Panel directory won't tell you that.
They won't tell me which specific box... but they will give me an idea where to start looking.


14, as stated was "Kitchen hall bath basement lights". 11 is marked "Kitchen outlets". Now, where do you think those two circuits would share a box?
 

Another C10

Electrical Contractor 1987 - still at it ..
Location
Southern Cal
Occupation
Electrician
I like this game .. first of all forgive me but I hate acronyms, just type the dang word..

I'll try to vision what I read, customer shows you his idiot pen aka sorry, also known as, the widow maker. I've had that happen with a client showing me their new toy .. nice I tell them hoping they'll go away. Anyway .. I didn't get much out of the light show with the clients pen so I'd either open the 3 way system up make sure it's wired properly at each end reading its configuration and or start at the breaker that appeared to be the indicator of the issue resulting in half the house cutting out. although it appearing to only cut out 1/2 a main breaker. with out going through all my techniques chances are the white may of been used as a common or traveler of the 3 way system and somewhere along the line became connected to an actual return therefor heating up a mains thermal quicker than the 15 branch circuit. Which by the way is quite a strange thing other than I presume the main breaker could be more sensitive than the Branch Breaker tripping seconds earlier, I'm sure an engineer knows that answer.
 

Another C10

Electrical Contractor 1987 - still at it ..
Location
Southern Cal
Occupation
Electrician
Sorry I didn't realize this thread was well into the hunt .. I responded based on the 1st 10 posts
 

Another C10

Electrical Contractor 1987 - still at it ..
Location
Southern Cal
Occupation
Electrician
So cycling breakers 3,4,7,8,11,12,15,16,19 and 20 shows that turning off 11 turns off power to the terminal of breaker 14.

This means breakers 11 and 14 are tied together somewhere. But instead of opening boxes, I just read the panel directory.

14, as stated was "Kitchen hall bath basement lights". 11 is marked "Kitchen outlets".
Never rely on the panel directory, try it as a search point yes but try not to believe it is true. breakers get moved, quick resolve disconnect # 14, no need for two feeds. At least for the time being the main wont be tripped , if they were on the same phase one would never know the problem was there. Although it is a problem obviously.
 

Another C10

Electrical Contractor 1987 - still at it ..
Location
Southern Cal
Occupation
Electrician
They won't tell me which specific box... but they will give me an idea where to start looking.


14, as stated was "Kitchen hall bath basement lights". 11 is marked "Kitchen outlets". Now, where do you think those two circuits would share a box?
Dishwasher / Garbage Disposer almost always are the two kitchen circuits at common point. Although keep in mind the location of the nearest 14 circuit and the closest 11 circuit to one another is were I'd start, I at times put a little square of electrical tape on all the devices affected then look for a practical wiring path. almost always saves me hours.
 
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480sparky

Senior Member
Location
Iowegia
Never rely on the panel directory, try it as a search point yes but try not to believe it is true. breakers get moved, quick resolve disconnect # 14, no need for two feeds......
Bad idea. Breaker #11 is a 20a with 12ga wire, Breaker #14 is a 15a on 14ga.

Dishwasher / Garbage Disposer almost always are the two kitchen circuits at common point. Although keep in mind the location of the nearest 14 circuit and the closest 11 circuit to one another is were I'd start, I at times put a little square of electrical tape on all the devices affected then look for a practical wiring path. almost always saves me hours.
Well, given that one circuit is for Kitchen Receptacles, and the other is for Kitchen Lighting... think about where, in a typical kitchen, those two circuits would share a box.
 
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