Fridg and microwave on multiwire branch circuit?

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smallfish

Senior Member
Location
Detroit
Code requires that a refridgerator be wired into the small appliance branch circuit or on an individual branch circuit. Do you see any problem with a refridgerator and a microwave being on a multiwire branch circuit? Is it code compliant on a multiwire branch circuit?
Thanks
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
I don't see why you can not use a MWBC for the fridge and microwave.
 

gndrod

Senior Member
Location
Ca and Wa
MWBC...

MWBC...

I don't see why you can not use a MWBC for the fridge and microwave.

Hi Edward,
In the old days I would have agreed, but in new resi wiring...not any more. The MWBC will not allow the CAFCI to function when both loads are operating. Even if the two BC's were not AFCI protected, there is a problem when the refer kicks in while the micro is running...and due to line coupling in the 3 wire NM cable feeding the SA, the device fault interrupter on the kitchen circuit will disconnect. Recently I replaced a GFCI on the counter that shared a micro and the kitchen SA#1 circuit. Both circuits were sharing the neutral when they were simultaneously activated. Seems the owner held the reset down on the GFCI while both appliances were operational. That fried the GFCI. What can be said about idiot proofing? Also note that MWBC's are obsolete in NM wiring if X10 or plc controls are added to shared BC functions. I hope this helps.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I thought that most if not all GFCI receptacles these days had trip free reset buttons like breaker handles.
The frying came from keeping the momentary trip coil constantly energized?
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Hi Edward,
In the old days I would have agreed, but in new resi wiring...not any more. The MWBC will not allow the CAFCI to function when both loads are operating. Even if the two BC's were not AFCI protected, there is a problem when the refer kicks in while the micro is running...and due to line coupling in the 3 wire NM cable feeding the SA, the device fault interrupter on the kitchen circuit will disconnect. Recently I replaced a GFCI on the counter that shared a micro and the kitchen SA#1 circuit. Both circuits were sharing the neutral when they were simultaneously activated. Seems the owner held the reset down on the GFCI while both appliances were operational. That fried the GFCI. What can be said about idiot proofing? Also note that MWBC's are obsolete in NM wiring if X10 or plc controls are added to shared BC functions. I hope this helps.
:?:? My whole kitchen is wired up with MWBC... going on fifteen years since I did the remodel. Nothing like what you described has ever happened. I don't fret that it will.
 

gndrod

Senior Member
Location
Ca and Wa
Safety in numbers

Safety in numbers

:?:? My whole kitchen is wired up with MWBC... going on fifteen years since I did the remodel. Nothing like what you described has ever happened. I don't fret that it will.

Hi Dave,
More power to both of us. I remoded my place 30 years ago and MWBC still works for me. I just know that I would get spanked if I tried it now.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
Hi Edward,
In the old days I would have agreed, but in new resi wiring...not any more. The MWBC will not allow the CAFCI to function when both loads are operating. Even if the two BC's were not AFCI protected, there is a problem when the refer kicks in while the micro is running...and due to line coupling in the 3 wire NM cable feeding the SA, the device fault interrupter on the kitchen circuit will disconnect. Recently I replaced a GFCI on the counter that shared a micro and the kitchen SA#1 circuit. Both circuits were sharing the neutral when they were simultaneously activated. Seems the owner held the reset down on the GFCI while both appliances were operational. That fried the GFCI. What can be said about idiot proofing? Also note that MWBC's are obsolete in NM wiring if X10 or plc controls are added to shared BC functions. I hope this helps.

MWBC not working with single pole AFCI I do agree with. But MWBC for circuits and GFCI will work fine and that is all I do for kitchens and bathrooms, unless an AFCI is required.
 
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