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#196798 10/27/10 08:21 PM
Joined: May 2003
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I had a customer call today, he was wondering if his main panel could be moved as it was in a basement suite kitchen. on the wall behind the cooktop stove and counter.

Anyhow when I looked in the panel someone had loaded it up with tandem breakers on 3 wire circuits. I think some of these circuits are split appliance circuits and they took out the double pole breakers and installed tandems to free up spaces.

A home inspector had took off the panel cover and told the buyer everything was fine.

I am sure the use of the tandem QO breakers on a 3 wire circuit (mwbc) is a violation am I right ??

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Doug:
This side of the border, you are 100% right. Guess some of our HIs moved up to you?



John
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I would say there was at least 8 tandem breakers with reds and blacks on them. doubled up neutrals landed under each screw on the neutral strip also.

It was tesla that actually made me aware to look for this when i saw the tandems

https://www.electrical-contractor.n...l_to_find_open_neutral_i.html#Post196375

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If the 3 wrie circuits have both side on the same leg it is definitely a violation. If he still managed to keep the phasing correct on the circuits it could be fine. Only circuits where both legs land on the same device(split wired receptacle) are handle ties/double pole breakers required.

jdevlin #196810 10/28/10 12:52 PM
Joined: May 2003
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Originally Posted by jdevlin
If the 3 wrie circuits have both side on the same leg it is definitely a violation. If he still managed to keep the phasing correct on the circuits it could be fine. Only circuits where both legs land on the same device(split wired receptacle) are handle ties/double pole breakers required.


humm I thought all multiwire branch circuits required a 2 pole breaker mainly because the neutral would still be energized

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G
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The handle tie/ two pole breaker question depends on which code cycle was in effect when the work was done. Current 2008 code cycle calls for ALL multiwire branch circuits to be simultaneously disconnectable, not just those on a common yoke. MWBC's terminated on the same phase sharing a common neutral would be a violation if the neutral is not oversized, something that just doesn't happen in resi construction.

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This is direct from ESA last month. Please note this is the CANADIAN code forum. Rules are different in NEC world.

Quote
If wiring a dedicated circuit can 1/2 of a multiwire circuit be used as a dedicated circuit.

Example can a 14/3 be pulled to the fridge receptacle and black and white for fridge and then red and white used for lighting?

Is a double pole breaker required or can two singles be used if proper installed on opposite legs of the service?


--- (yousefr) 9/16/2010 9:48:36 AM
1. Each side of a 3-wire circuit can be considered as a separate dedicated circuit if they are properly connected to different phases and have common neutral.

2. Yes, a double pole breaker or two singles can be used (if properly installed on opposite legs of the service) for a 3-wire circuit.

Reference is to the Ontario Electrical Safety Code 24th Edition/2009.



Ray Yousef
Assistant Code Engineer

Last edited by jdevlin; 10/28/10 04:06 PM.
jdevlin #196815 10/28/10 06:48 PM
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Thanks
jdevlin

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I didn't see that this was a Canadian code question before I answered. Sorry.

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The term Tandem can cause some confusion. There was a tandem breaker that used 1 pole from the bus and had 2 15 amp ccts available. This breaker would not be appropriate for a shared neutral unless the neutral was good for 30 amps and even then would still not be code compliant. there are also side by side mini breakers that also used a single pole off the buss. Again this would not allow a common neutral.
To share a neutral whether for 2 circuits from a 3 wire or a split receptacle both current carrying poles must come from a different phase so the voltage between poles is 240 volts and not 0 volts, In both cases there would be 120 volts to ground or neutral.
In the case of a split plug a 2 pole common trip breaker or tie bar is required.
A 3 wire circuit supplying 2 different loads and not on a receptacle with a common yolk can use 2 1 pole breakers on adjacent phases without requiring a tie bar.

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