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demandrew 12-19-2011 09:53 PM

Dealing with split-circuit receptacles
Hi all,
I'm re-wiring the receptacles for my new kitchen and I've discovered that the available power is from a split 15 amp circuit.
What has me a little confused is how the old outlets were wired so I wanted to ask you all about it here. There was a run of three receptacles, with the red hot powering the first all by itself, the black hot powering the subsequent two, and a common neutral and ground throughout.
Am I correct in thinking that this is not up to code and sort of defeats the purpose of having split-circuit in the first place?
Aside from possibly being against code, is there anything terribly wrong with such a setup? - With using a split circuit to power seperate receptacles rather than just each half of the same receptacle? I only ask because this seems to be the only way I could install GFCIs, which one cannot, if I understand correctly, install on a split circuit.
Any comments? Any general code guidelines when dealing with split-circuit?

Billy_Bob 12-19-2011 09:58 PM

They are called MWBC or MultiWire Branch Circuit.

Search for those terms.

This is an "electrical trick" which takes advantage of Alternating Current. While one wire is using the electricity one "direction", the other is using it in an opposite "direction". They balance themselves out on the one neutral.

joed 12-19-2011 10:02 PM

What you are describing are NOT split wired receptacles. Split wired would have both black and red on the same receptacle and the tab cut. You have a multiwire branch circuit.

You need to post you location and the amperage of the circuit to know if it is up to code.

demandrew 12-19-2011 10:31 PM

Thanks for the quick replies.
I'm living in Toronto, and I believe the circuit is 15 amps across two breakers that are connected to each other. (Probably a little old)
I knew that they weren't set up as split-circuit, and yes none of the tabs were cut. My confusion was that I thought the two hot wires meant they were supposed to split-wire the receptacles but just chose not to. So it seems that just because I have two hot wires it doesn't mean I have to split-wire receptacles but might instead use the "trick" that billybob speaks of? At any rate, I will look into MWBC. Thank you both for bringing it to my attention!

AllanJ 12-20-2011 05:46 AM

When you have a 120/240 volt multiwire branch circuit with two hots and one neutral, daisy chaining from one outlet box to the next, then ground fault interrupters demand one of the following:

1. A single 120/240 volt GFCI breaker at the panel,
2. Individual GFCI receptacles in each and every outlet box,
3. One GFCI receptacle at the first outlet box for the black hot serving that box only and one GFCI receptacle at the second box for the red hot serving all remaining boxes.
4. After the first outlet box (with a GFCI unit) a separate hot and neutral pair continuing downstream for the GFCI protected (load side) continuation from the first GFCI.

YOur situation can have GFCI units installed as #3.

SPlitting the halves of a duplex receptacle can also be done with separate hot and neutral pairs (non-MWBC wiring) when the tabs between the screws are broken off on both sides of the receptacle. Both circuits must go to breakers with handles tied together.

Originally Posted by Billy Bob
This is an electrical trick which takes advantage of Alternating Current ...

Psst! It works for direct current also, provided you get the polarity right, for example plus 6 volts for one hot and minus 6 volts for the other hot relative to a shared neutral. This is not a good automotive example because a 12 volt battery does not have a center tap for plus or minus 6 volts.

joed 12-20-2011 07:22 AM

This is a Canadian kitchen. You need to specify your location. It makes a difference on the answer you get.

You are correct. 15 amp receptacles on the counter are not permitted. You must wire them as split wired receptacles. If you want to install GFCI then you need either 15 amp double pole GFCI breaker or run 20 amp circuits and use 20 amp T slot GFCIs.

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