Need some advice on a MWBC

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  #1  
Old 06-11-13, 01:02 PM
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Lightbulb Need some advice on a MWBC

Hello everyone, Long time lurker first time poster here.

I am doing a retrofit of some florescent lights and some outlets and need some advice.

I have removed all of the existing fixtures and replaced with recessed cans. So that part is done and completed. However i need some help thinking through the existing MWBC.

(this is all 20amp by the way)

There is a junction box in the ceiling that has an MWBC in it. One half (red) fed the florescent fixtures which i used to install the recessed fixtures. The other half (black) was used to goto a receptacle in the ceiling. I capped this black wire originally and am now wanting to add more receptacles off of this black wire and a shared neutral.

I have a diagram of the circuit. Could someone take a look and let me know if this is legit? The breakers are installed in a Square D box single phase numbers 2 and 4 so they are on opposite poles. From my understanding of MWBC this is ok as long as the handles are tied or i convert it to a double pole...

Any advice is appreciated.
 
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Old 06-11-13, 01:12 PM
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Yes looks good. Is this a finished basement?
 
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Old 06-11-13, 01:14 PM
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Thanks Ray, its an older commercial storage room The reason for not wanting to add another 12/2 (ideal) is because the box is in CMU wall with concrete ceiling and floor.
 
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Old 06-11-13, 01:25 PM
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Then should be okay. My question was based on thinking it was residential where GFCI or AFCI protection might be needed.
 
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Old 06-11-13, 01:29 PM
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Yes, this is a storage room with dedicated equipment that shouldn't total more than 17 amps on both circuits combined (8 x 65w lights) then 12 amps dedicated equipment on outlets
 
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Old 06-11-13, 03:01 PM
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It looks to me as if you don't need GFCI or AFCI units but if you did, you can install them on one or both sides of the circuit after the circuit splits apart (at the middle junction box as shown) and no special treatment is needed.

If you wanted to install a GFCI or AFCI unit in the panel, the unit must be for a MWBC (for a 120/240 volt circuit).
 
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