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kevcard

Member
Location
New Jersey
First off I got to say I have been reading here for awhile now. I got some very good info and advice so with my first post I need some help.

I went on a service call this week. The customer calls with a dishwasher tripping the breaker. The house is less then 2 years old. There are two dishwashers in the kitchen. They are wired on a MWBC (12/3 NM to a junction box with 12/2 going to each dishwasher). Only one dishwasher was tripping a breaker. I put an amp probe on the circuit. That was normal. Voltage was normal. I check insulation with a Megger. All wires checked open. The only thing I could find was that when I shut off only one circuit, I would have 24volts on it. I reversed that and shut the other circuit off and turned the first circuit on and would get 24 volts on the dead circuit again. I just figured that was an induced voltage I was reading. So I went out to the panel and swapped the wires and told the customer to call me when it trips again. I wanted to see if it was the dishwasher. Well I got the call. The other dishwasher is tripping now. So it is in the circuit somewhere. I asked if both dishwashers were running when the breaker tripped.
They said they were. Any ideas?
 

jbelectric777

Senior Member
Location
NJ/PA
mwbc's are ok for an experienced electrician (new code by the way both have to open and be on a two pole 2008 NEC) but 24 v is way too high for induced voltage or even capacitance. when you have both circs off do you read anything between each dishwasher circuit? it sounds like someone tied something in where they shouldnt have, look for junction boxes, open other boxes and check, last resort run 2 new dw lines. before that turn off all the other circuits in the house and see if anything else stays on, lift each neutral and check for a small load when you tap it on the neutral bus bar, be carefull and ware gloves because the load of a dishwasher thru you hurts if ya know what i mean........ ouch !!!!!!!!!!!!!!!!!!!! good luck, hope that helps
 

kevcard

Member
Location
New Jersey
I will swap out breaker when I go back out just for giggles.

I forgot to add that these dishwashers are being fed from a sub panel. From what I seen there is no other junction box, HR from panel. Now that you mentioned it, there might be something with the neutral in the sub. I will look into that when I go back. Costumer going away for a week starting tomorrow.

Thanks
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Kevin, welcome to the forum! :)

. . . I went out to the panel and swapped the wires . . .

The other dishwasher is tripping now. So it is in the circuit somewhere.

Any ideas?
Put them back where they were (I guess you don't have to), and try swapping the hots at the JB where the two circuits split.

Part of the process of elimination. I bet the problem is one of the dishwashers, not the circuit.
 
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kevcard

Member
Location
New Jersey
True, with the typical volt-meter, which is why I prefer a solenoid-type tester for troubleshooting.

And, Kev, don't let the MWBC bother you. I'd have likely run one, too.

I will have to find my old solenoid meter and throw it on the truck.
I don't mind the MWBC. I just never liked it in a Resi install for safety( been using 2 pole breakers since the 80's) reasons. With the new code I guess I can go back to it.
 
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