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Any Problem having #10 wire and #12 wire on same cuircuit? Gfci ok on Washer?

Any Problem having #10 wire and #12 wire on same cuircuit? Gfci ok on Washer?


Old 05-10-11, 07:44 PM
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Join Date: Sep 2003
Location: USA
Posts: 166
Any Problem having #10 wire and #12 wire on same cuircuit? Gfci ok on Washer?

We have a Washer Dryer and 2 refregirators on a 20 amp line. We moved the line from our main panel to a subpanel about 4 feet away. Then we ran #12 wire about 20 feet to a junction box which had #10 wire going to a outlet which the washing machine and dryer plugged into, and two other outlets which the fridges plugged into, These were all 120 lines.

The old line used #10 wire however it was on a 20 amp breaker. It being a 20 amp line we figured we could use #12 wire the first 20 feet

Question #1
Is there any problem mixing #10 line and #12?

in doing this project we decided to add a gfci right next to the cuircuit breaker to cover all items on cuircuit.

A repairman came out today and tripped the gfci in trying a repair. I went out and reset the gfci but not the breaker.
He tested the line and said our voltage was low like 75 watts then a second later he said it was like 119 then held at 120. Then he said we had the polarity reversed or something was wrong.

Then he told us not to have our washing machine on a gfci it would just trip all the time that I should rewire it. (though we have had it a couple weeks on it and it hadn't tripped once until he got there).

Then after that only one of the outlets were working where the washing machine was plugged into. He left a bit to get a part he needed and while he was goneI checked the outlet with my Kill a Watt meter and got a reading of 122 on one side of the receptacle and like 122.2 on the other.

He came back installed the part with one part of outlet not working and said we needed to check our work we had done. when he left I then went out and turned the breaker off and turned it on again and the second part of the receptacle worked.

I got my little $5 polarity checker thing and it lighted up the outlet was wired correctly according to it (Its been there for 30 years). I just checked outlet now a few hours later 122.9 and 123.0 and both outlets work.

Question #2
is it ok to leave the Gfci on or do I need to remove it?
Question #3
Is there something wrong with the wiring or did It just partialy trip the main breaker or something when he knocked the Gfci out and when I reset it It should be good to go?
Question #4 Do I have a wiring problem is washing machine safe to run? (repairmen said insurance will charge us for next repair if there is a wiring problem)?

Thanks for all your help!
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Old 05-10-11, 08:17 PM
ray2047's Avatar
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Join Date: Mar 2006
Location: USA
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Newer codes require a GFCI in the laundry room. So long as the circuit protects the smallest size wire larger size wire is ok. As long as you breaker doesn't exceed 20a you are fine.

Best guess the laundry was wired for an electric dryer. The 120/240v #10 cable for the electric dryer was changed to a 120v 20 amp circuit when a change to a gas dryer was made.
Old 05-11-11, 01:03 AM
Thread Starter
Join Date: Sep 2003
Location: USA
Posts: 166
thanks reply.

I am actually the one who wired the #12 wire into the #10 about 2 weeks ago. However you are correct we do have a Gas dryer now and it may have been electric 40 years ago and thus the need for #10 wire.

So no problem mixing #10 and #12 thank you!

I guess my real question is then, is it safe to run the Washing Machine on that outlet, the tech said we could burn the motor running it with voltage below 115 and he said he had a reading breifly of 75 at one point.

I keep taking readings currently and it keeps showing 122.0 ish like 121.9 121.8 122.0 and that it is wired correctly.

Can a trip of a gfci and maybe not a full reset of a breaker cause misreadings temporarily or one plugin of a receptacle to misfunction

bottom line is it safe to use the Washing machine?

Thanks reply!
Old 05-11-11, 02:22 AM
pcboss's Avatar
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Join Date: Jul 2002
Location: Maryland
Posts: 14,357
The quality of the voltage reading depends on how well the probes make contact with the energized parts.

Like Ray said, GFI protection is now required for washers within 6' of a laundry tub.

Motors do not like low voltage, but a GFI will not cause it.

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