Anyone good with house wiring diagnosis?

Ron342 · 03-25-19, 02:43 PM

Yesterday a 120v breaker tripped in our bedroom circuit with very little connected. No recent construction efforts i can figure to cause it so unplugged everything, still trips so looked into the boxes.
First one i looked at had a socket and branched out in 2 directions from there.
s
Separated the 3 blacks, tried the breaker, no trip, located one black as the hot then read resistance between the black of each branch circuit and the still ganged together whites and also to the grounds. Both read high open circuits (megohms)
Then connected one branch black to the hot black, no trip, but when i tried the hot to the other branch black it tripped big.
What am i missing here? how can it trip on one branch if both branches are reading as open circuits between the blacks and ganged whites and grounds?
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MN Renovator · 03-25-19, 03:45 PM

Intermittent connection or it might need voltage to bridge a gap and start an arc. At lease you've figured out which side of the branch is causing the dead short allowing you to leave it disconnected while you trace where it's going and find out where the electrical gremlin is.

jeff5may · 03-25-19, 11:23 PM

I agree, AC isn't as well behaved as low voltage DC. At least you seem to have a line that's staying how is. Much easier to get rid of that way. It all depends on how the defect came to be as far as the cause. Overloading causes different problems than loose or uninsulated connections. Since the branch is tripping the breaker, there should be some evidence to prove it once you find the issue. Arc Burns or melted insulation or something similar.

philb · 03-26-19, 08:48 PM

If you have any GFI or arc fault plugs, check those out. The GFCI's have given me problems thats hard to trace. Replace them or take them out of the circuit.

03-25-19, 02:43 PM	#1
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	Anyone good with house wiring diagnosis? Yesterday a 120v breaker tripped in our bedroom circuit with very little connected. No recent construction efforts i can figure to cause it so unplugged everything, still trips so looked into the boxes. First one i looked at had a socket and branched out in 2 directions from there. s Separated the 3 blacks, tried the breaker, no trip, located one black as the hot then read resistance between the black of each branch circuit and the still ganged together whites and also to the grounds. Both read high open circuits (megohms) Then connected one branch black to the hot black, no trip, but when i tried the hot to the other branch black it tripped big. What am i missing here? how can it trip on one branch if both branches are reading as open circuits between the blacks and ganged whites and grounds? Case of your favorite beer (within reason) delivered as a reward!!

03-25-19, 03:45 PM	#2
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 940 Thanks: 41 Thanked 117 Times in 91 Posts	Intermittent connection or it might need voltage to bridge a gap and start an arc. At lease you've figured out which side of the branch is causing the dead short allowing you to leave it disconnected while you trace where it's going and find out where the electrical gremlin is.

03-25-19, 11:23 PM	#3
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	I agree, AC isn't as well behaved as low voltage DC. At least you seem to have a line that's staying how is. Much easier to get rid of that way. It all depends on how the defect came to be as far as the cause. Overloading causes different problems than loose or uninsulated connections. Since the branch is tripping the breaker, there should be some evidence to prove it once you find the issue. Arc Burns or melted insulation or something similar.

03-26-19, 08:48 PM	#4
philb Apprentice EcoRenovator Join Date: Nov 2010 Location: Oklahoma City Posts: 155 Thanks: 58 Thanked 17 Times in 14 Posts	If you have any GFI or arc fault plugs, check those out. The GFCI's have given me problems thats hard to trace. Replace them or take them out of the circuit.