Multwire circuit Q

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Old 08-07-09, 11:33 PM
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Multwire circuit Q

When plug outlets are required to be supplied with a circuit used for no other purpose, in my situation Kitchen eating area, dishwasher, if I run a 12/3 [ 2SP 20 A Brkrs on diferent phases ]] use one circuit for the dishwasher the other for the eating area will this comply with the requirement ''to be supplied with a circuit used for no other purpose''?

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Old 08-08-09, 04:20 AM
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You'll need to handle tie those breakers since it's a MWBC.
Those eating area receptacles may have to be arc-fault protected if you're under the 08 code. So this may be difficult to do since one will be AFCI and the other not.

I've never used a double pole AFCI breaker, not even sure if they're available or how it would work tying the handles of 2 single poles together.

I would just use a MWBC on 2 circuits not requiring AFCI.
 
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Old 08-08-09, 11:15 AM
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Thank you for reply,I dont need AFCI for the KEA in my localI make sure I get the correct breaker
Cheers
 
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Old 08-08-09, 03:49 PM
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Mwbc

by no other purpose, means it's a dedicated circuit, and thus only serves a dishwasher, garbage disposal, microwave, FAU and so on, and so the feed stops at the one receptacle and does not daisy chain any where else.

to that end if you feed with 20 amps to one receptacle, you must use a 20 amp ( not 15 ) amp receptacle. if you are feeding 2 circuits going to 2 different locations, and one happens to be just one duplex on one circuit, and the other a series of duplex on the other circuit, you do not need a common trip handle. only when both circuits terminate at the same yoke ( duplex receptacle ) do they need to be common trip tied. this is why a 12/3 is usually run to one receptacle for the dishwasher / garbage disposal set up ( under the kitchen sink ) tied into a common trip combo ( or 2 pole full space not slim ) breaker. the issue is for safety so you do not have one half of the receptacle hot if you pull out the duplex for servicing.

other than that what you got will be fine, and the outlets in the kitchen ( general purpose not counter top ?? ) can be 15 amp outlets if there is more than one on the 2nd circuit.

In the 2005 NEC, Section 210.4(B) applied only to installations where a multi-wire branch circuit supplied more than one device or equipment on the same yoke, such as a duplex receptacle with the “hot” side jumper removed and “hot” conductors from different phases connected to each receptacle. If the neutral conductor was connected to the neutral side of the receptacle and it was common to both receptacles on the yoke, a disconnecting means was required to simultaneously disconnect all the ungrounded conductors. Either a common trip circuit breaker could be used or individual single-pole circuit breakers could be tied together using an identified handle tie. The purpose of this section was to ensure both ungrounded conductors supplying the two devices on the single yoke would be disconnected.

The change in Section 210.4(B) for the 2008 NEC has expanded the requirement for each multiwire branch circuit to be provided with a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates. This text no longer applies only to two devices on a single yoke; it applies to all multiwire branch circuits supplying any load. For example, prior to the 2008 NEC change, a multiwire branch circuit could supply the overhead lighting system with three single-pole circuit breakers. Handle ties would not have been required. With the change in 210.4(B), these breakers must be disconnected simultaneously. Since circuit breaker handle ties are not designed for connection to three single-pole circuit breakers (only two), a three-pole internal trip circuit breaker must be used.

Because of the dangers associated with a multiwire branch circuit, 300.13(B) specifies that the removal of a wiring device, such as a receptacle shall not cause an interruption of continuity for the grounded (neutral) conductor. Therefore, the grounded (neutral) conductors for multiwire branch circuits shall be spliced together, and a pigtail shall be provided for device terminations.
 

Last edited by mikerios; 08-08-09 at 04:12 PM.
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Old 08-09-09, 11:08 PM
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Thanks so much for your patience to explain
 
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Old 08-10-09, 09:16 AM
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Originally Posted by RODEL View Post
use one circuit for the dishwasher the other for the eating area will this comply with the requirement [I][B]''to be supplied with a circuit used for no other purpose''
Yes, you could use a multiwire circuit for this application; HOWEVER, it's almost always far more trouble than it's worth. Often with the bulk price rates between 12/2 and 12/3 you won't even save any money on wire unless you need to buy a lot of 12/3.

If you used the MWC, a double-pole 20A breaker would be required.
 
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Old 08-10-09, 09:19 AM
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Originally Posted by wirenut1110 View Post
I've never used a double pole AFCI breaker, not even sure if they're available or how it would work tying the handles of 2 single poles together.
They do make double-pole AFCI in 15A and 20A now, but be ready for the invoice! $$$$ I guess compared to rewiring a bunch of MWCs throughout an old house it's worth it, but certainly not something I'd plan to use if I didn't have to.

You can't handle tie single pole AFCI because the GFCI component would trip just like a standard GFCI on a shared neutral.
 
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