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Breaker in house tripped by outbuilding with separate service

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N

NC4

Member
Location
Raleigh NC
Occupation
Retired
First off, I am not an electrician. But, I have a problem that has stumped a few. Here’s the scenario.

My house was built in 1997. 200A underground service from utility box near street. In 2021 we built a completely separate building on the property about 200 feet from the house. We had a separate 200A service and meter installed to the new building. I was there when the power company dug and installed the lines. There is no connection between the house and the building other than a plastic water line that runs from the well to the house and then on to the building. In the building there is a point of use water heater. 220v, 50A breaker on 6AWG wire. We rarely use it.

In 2022 we had some renovation work done at the house. The electrician patched in to existing wiring to add some outlets and lights upstairs and as part of that changed a breaker to AFCI/GFCI. Everything worked fine for awhile until I retired and then we noticed the house upstairs breaker would occasionally trip. We went through extensive troubleshooting for about 6 months. Removed all devices and loads, replaced breaker, inspected all wiring and boxes in circuit, traced things, etc. Nothing looked wrong in the panel, and so on. The random trip continues.

Several weeks ago, just by accident I figured out that when I use the hater heater in the separate out building, it triggers the trip of the breaker in the house. How can that be given they are on separate feeds and separate meters? Any ideas on how to further troubleshoot and fix? Thanks.
 
Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
ptonsparky said:
You would think that noise would be attenuated by the time it got to the house. Replace the breaker might be the first option.
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OP said the breaker was replaced. However, he didn't say whether the tripping breaker was the DF (AFCI/GFCI) or a regular breaker. I can only guess it was the former as there is no way the regular breaker could trip from another load, from a completely separate service.
 
N

NC4

Member
Location
Raleigh NC
Occupation
Retired
The breaker in the house, the one that trips, has been replaced twice. Siemens combo AFCI/GFCI 15A. The one in the building with the water heater, doesn’t trip and is a regular Siemens 50A.
 
N

NC4

Member
Location
Raleigh NC
Occupation
Retired
The water heater is constantly powered. It is the kind that turns on the heater elements when it senses water flow.
 
C

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
Maybe check the voltage when the water heater is off then turns on. It could be the utility has a poor connection somewhere and the voltage is dropping enough for the DF breaker to sense low voltage. If this were the case I would thing you would be seeing lights flickering but its worth the test.
 
N

NC4

Member
Location
Raleigh NC
Occupation
Retired
Currently there is “no load” on the circuit at the house. Everything unplugged or switched off at wall. No smart devices plugged in. Since I have tied it to the water heater scenario I have seen it trip both with things plugged in and with no load. We have done a very extensive search and trace of house wires and are certain of the circuit path and connections.

It’s a very strange thing to think that noise from the heater would travel through the wires to the utility box (275 feet) and then to the house (another 250+ feet).

When the breakers (original and new) trip neither of the LEDs on the breaker are lit. So I can’t say for sure if it’s an arc, ground, or load fault. I assume arc since that seems the most fussy part of the breaker. Would it be worth swapping in a GFCI or AFCI breaker for temporary troubleshooting? Not sure what would be gained by that if it makes a difference.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
If both buildings are on the same transformer, could be the Triac’s that control the heating elements cycling enough to make the arc fault breaker to think there is an arc, but you should have other arc fault breakers tripping too. The poco had a loose connection at the transformer at my house, I would randomly have several arc faults trip within seconds of each other, so arc faults do detect faults on the line side too. Try turning on all of the hot water faucets on, then turn on the breaker to the tankless water heater to see if it trips the arc fault. Due to the flow, the triacs should not be pulsing.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
To confirm its a arc fault issue you could replace the AFCI/GFCI with just a GFCI breaker.
Personally if the GFCi did not trip I'd be tempted to forget about it.
It could be that the demand water heater as found a POCO connection issue for you.
 
N

NC4

Member
Location
Raleigh NC
Occupation
Retired
Ok, now I’m getting something to go on! Thank you all for your responses, this has been an aggravating issue which got even more frustrating when I found the illogical scenario between the out building water heater and the house breaker.

I did the test that @hillbilly1 suggested. Turned off the breaker to the water and opened everything up to full blast Hot water. Ran until the water was very hot and then shut off the heater at the breaker. NO trip at the house! Waited awhile and then turned heater breaker on again with faucets closed. Cracked the hot and cold open a little as you would do washing your hands. Paid a little extra attention to the hot feeling of the water. You could actually feel the water temp oscillating from warm to slightly cooler to back to warm again. You might only notice if you were looking for it. Bingo, house breaker tripped!

So now that I think I know what is causing the issue, is there anything else I should check? Maybe have power company check the service connections in case the water heater is just adding to an existing problem elsewhere? Hate to spend more $$$ on the new heater as @ptonsparky suggested and then still have an issue.

Again, you professionals are great and over the years I’ve learned so much from this community.
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
It seems to me that there may be an issue with the water heater if it's new I would see if they would replace it. I still don't understand how it could affect the house that far away but it appears to be a problem with the water heater especially when you said the temperature is changing as you were using it
 
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