MWBC Question


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Old 02-21-14, 10:37 PM
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MWBC Question

Hi -

I would like to convert a single, dedicated, 20 amp circuit to a MWBC. It's a line for my home theater amp, and I'm adding a second amp that needs another dedicated 20 amp line.

The run is only about 4ft. from the panel and I think I can avoid cracking open the sheet rock if I can use a 12/3 run.

Is it OK to run it as follows -

Duplex 20 amp braker (newer square D box)
12/3 with hot off each breaker section
Break the tab on the 20 amp plug making it a separate feed receptacle
Neutral and ground as normal

IF the above is OK then -

Do they make a piece that will tie the two duplex breaker switches together?

I'm really not worried about any person related safety issues while I remain the current owner as the plug is behind false walls that require me to remove (meaning a repair man won't be in the house and for some odd reason access this plug- or the like).

What would be the proper way to leave this circuit should I sell the house? Wall plated off with some kind of 'tag' inside or??

Just want to have all the bases covered both for current and future.
 
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Old 02-21-14, 11:01 PM
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You can not use a duplex breaker as both of those poles are on the same leg. You can use a 240 breaker. It would be a 2 pole QO-20A. Only one handle..... nothing to tie together.

In the future you could replace the receptacle. Use the white and blacks wires. Cap off the red.
Replace the 2 pole breaker with a single pole 20A and cap off the red wire.
 
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Old 02-21-14, 11:26 PM
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Oh yes yes..... I forgot duplex uses the same exact leg for both hots.

I'm out of space, so I would have to combine two singles with a duplex to make room for the double.

I could, although certainly not ideal, use two single 20 amp breakers instead of the one 20 amp/240 volt, correct?

I understand that's not code. I ask more to make sure I'm understanding the breaker box and 'separate' legs situation.
 
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Old 02-21-14, 11:54 PM
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Yes.... you could use two single breakers with a tie handle. The breakers would have to be one above the other.
 
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Old 02-22-14, 12:02 AM
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Gotcha. I'm understanding the opposite leg correctly. It's confusing if you don't understand how a breaker box is laid out. One could think opposite legs means opposite sides.

One last question - I'm OK to use the 20 amp receptacle in separate feed mode?
 
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Old 02-22-14, 12:30 AM
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You need to use a 20 amp.
 
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Old 02-22-14, 12:32 AM
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Need to use a 20 amp what?
 
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Old 02-22-14, 03:25 AM
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You need to use a 20 ampere receptacle. This is because a 20 ampere circuit may have 15 ampere receptacles IF there are two or more places to plug in to (a duplex receptacle) but in a dedicated circuit as you propose there will be only one place to accept a plug for each 20 ampere circuit and therefore requires that single point to be rated at 20 amperes.
 
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Old 02-22-14, 11:00 AM
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Ok..... So it would make sense that a 20 amp dual receptacle meant for one circuit. that can be separated with the break of a tab to accept two circuits would not change its amp rating... Correct?
 
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Old 02-22-14, 11:15 AM
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Yes..... that is correct.
 
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Old 02-22-14, 11:25 AM
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I figured, but I like to make sure with this sort of thing. Thanks.
 
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Old 02-22-14, 07:00 PM
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I got the breaker pictured below and I have two ways I can use it.

Turns out I have another MWBC in the panel, bottom left. It's a kitchen circuit and I'm pretty sure but not positive that each circuit only controls one thing.

In any event they are on untied 20s. I can use my new quad breaker in this location, or I can use in the location marked on the upper right. I would located the one of those 20s to the lower right. The dedicated is indicating my line one of my NEW MWBC.

I'm going to go pull the new 12/3 I just got while I wait for opinions on which would route is better to take.

FWIW I couldn't find a square d quad that had ties on the inside two and outside two. I noticed some Cutler-Hammer have these.

Name:  IMG_2900 (Large).jpg
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Size:  47.1 KBName:  quad 20_20.jpg
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Old 02-22-14, 09:48 PM
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Ehhh.. I sat and I stared at it and decided I could do it right on both circuits by simply buying another double pole 20 for the bottom left spot.

So.... that's what I'll do.
 
 

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