GFCI - MWBC - GD, DW, SBAC

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ESolar said:
No
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That said - I just looked at the rated demands on mine: my Insinkerator 3/4 HP is 8.1 A, and my Bosch 500 DW is 12 A. But they are definitely not drawing that much. It gets rounded down - so spot on. Maybe they design these that way. 3/4 HP is kind of the minimum size GD without problems straining the motor at times. So Bosch does not want a DW drawing more than 12 amps and cutomers having to rewire their house - the need to rewire would turn off nearly everyone.
 
ESolar said:
That said - I just looked at the rated demands on mine: my Insinkerator 3/4 HP is 8.1 A, and my Bosch 500 DW is 12 A. But they are definitely not drawing that much. It gets rounded down - so spot on. Maybe they design these that way. 3/4 HP is kind of the minimum size GD without problems straining the motor at times. So Bosch does not want a DW drawing more than 12 amps and cutomers having to rewire their house - the need to rewire would turn off nearly everyone.
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But I don't think it's necessarily a simple sum of the two loads. Ill have to refresh myself with the applicable code section, and it depends on if fastened In place, cord and plug connected, etc.....220.23?
 
ESolar said:
That said - I just looked at the rated demands on mine: my Insinkerator 3/4 HP is 8.1 A, and my Bosch 500 DW is 12 A. But they are definitely not drawing that much. It gets rounded down - so spot on. Maybe they design these that way. 3/4 HP is kind of the minimum size GD without problems straining the motor at times. So Bosch does not want a DW drawing more than 12 amps and cutomers having to rewire their house - the need to rewire would turn off nearly everyone.
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I'll bet the DW draws about 10A when the heat/dry cycle is on. Not during the wash cycle, though, the motor only draws an amp or two.

Every dishwasher spec I've ever seen is roughly the same.
 
MWBC are not suited for today's GFCI and AFCI environment.

Also, in your diagram, the duplex outlet with the tab removed is not fed with a MWBC...both the outlets are on the same side. If you had this setup, you'd want that duplex with tab removed to be fed with the MWBC in the first place.
 
tthh said:
Also, in your diagram, the duplex outlet with the tab removed is not fed with a MWBC...both the outlets are on the same side. If you had this setup, you'd want that duplex with tab removed to be fed with the MWBC in the first place.
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Why is that if both appliances can be one a single circuit? He's feeding the duplex with one circuit from the MWBC. The other circuit is being used for one of the require SABC's.
 
infinity said:
Why is that if both appliances can be one a single circuit? He's feeding the duplex with one circuit from the MWBC. The other circuit is being used for one of the require SABC's.
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Except for the GFCI/AFCI breaker complications that MWBC now pose, of course, that's fine if both appliances can run on the same side. But, I'd never plan a new build with dishwasher and disposal on the same circuit. A kitchen remodel, yes, if getting one there wasn't going to be easy, but not a new build.
 
Can someone explain why AFCI poses problems for MWBCs? They've just switched to 2020 here, and previously they were not requiring AFCI on the SABC, but they may be now.

And I just realized that I have been typing SBAC instead of SABC - so the acronym jokes are on me.
 
ESolar said:
Can someone explain why AFCI poses problems for MWBCs? They've just switched to 2020 here, and previously they were not requiring AFCI on the SABC, but they may be now.

And I just realized that I have been typing SBAC instead of SABC - so the acronym jokes are on me.
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On just about everything now, you need either: a GFCI breaker, an AFCI breaker, or more likely a combo GFCI/AFCI breaker. The combo's exist in single pole. They are not commonly even made in double pole and are expensive. They are non-existent compleyely in tandems.

Yes, you can use GFCI, AFCI and combo GFCI/AFCI duplex outlets, but I hate having these things all over the place.
 
ESolar said:
Can someone explain why AFCI poses problems for MWBCs? They've just switched to 2020 here, and previously they were not requiring AFCI on the SABC, but they may be now.

And I just realized that I have been typing SBAC instead of SABC - so the acronym jokes are on me.
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Some earlier AFCI also had some degree of GF detection. Those could not tolerate a shared neutral on the load side.
 
So the objection to MWBCs is the lack of available combo breakers CAFCI/GFCI and the resulting need to wire GFCI outlets and CAFCI breakers? For example this breaker:
"The Siemens Combination Type 2-Pole AFCI meets or exceeds all requirements of AFCI circuit breakers required by the 2008 NEC. They are UL 1699 listed. The device is designed for two 120V circuits, with common trip. By design, the two phases of a Siemens 2-Pole Combination Type AFCI are on opposite phases, and therefore meet the requirement put forth in NEC 2011, Section 200.4. Like a single pole Combination Type AFCI, the 2-pole Combination Type AFCI comes with a 16” coiled ("pigtail") neutral connection, that is terminated at the neutral bar inside the load center. This wire may be cut to length as needed for a neat installation. The available products are detailed in the table below."
I guess in a tripping situation, that could have you running back and forth between box and outlet. But hopefully tripping is not happening. Also, is there anything gained by having AFCI and GFCI separated, e.g., if only the AFCI were tripping, doesn't that imply something about the problem for troubleshooting? As an example, the last AFCI tripping issue that I had was where someone had backstabbed and the wire was loose. That would not trip the GFCI, only the AFCI.
 
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ESolar said:
So the objection to MWBCs is the lack of available combo breakers CAFCI/GFCI and the resulting need to wire GFCI outlets and CAFCI breakers? For example this breaker:
"The Siemens Combination Type 2-Pole AFCI meets or exceeds all requirements of AFCI circuit breakers required by the 2008 NEC. They are UL 1699 listed. The device is designed for two 120V circuits, with common trip. By design, the two phases of a Siemens 2-Pole Combination Type AFCI are on opposite phases, and therefore meet the requirement put forth in NEC 2011, Section 200.4. Like a single pole Combination Type AFCI, the 2-pole Combination Type AFCI comes with a 16” coiled ("pigtail") neutral connection, that is terminated at the neutral bar inside the load center. This wire may be cut to length as needed for a neat installation. The available products are detailed in the table below."
I guess in a tripping situation, that could have you running back and forth between box and outlet. But hopefully tripping is not happening. Also, is there anything gained by having AFCI and GFCI separated, e.g., if only the AFCI were tripping, doesn't that imply something about the problem for troubleshooting? As an example, the last AFCI tripping issue that I had was where someone had backstabbed and the wire was loose. That would not trip the GFCI, only the AFCI.
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Answering myself - personally I would want to know if I had a GF or an AF issue.
 
rc/retired said:
Well, I might be confused.
In a commercial kitchen, I have no problem with the drawing. However, (there's always a however in life), in a residential kitchen, this is incomplete.
For residential, as stated, a dual function breaker is the way to go.
But, the SABC that supplies the the disposal and dishwasher does NOT meet the requirements for the 2nd SABC for residential kitchen counters.

Ron
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Does not fit the requirements for any SABC's if the DW and DSP are fastened in place as is typical. A portable dishwasher would be something that could plug into a SABC. Never seen such a thing as a portable disposer but if there were such a thing it could be also I guess.
 
ESolar said:
Can someone explain why AFCI poses problems for MWBCs? They've just switched to 2020 here, and previously they were not requiring AFCI on the SABC, but they may be now.

And I just realized that I have been typing SBAC instead of SABC - so the acronym jokes are on me.
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It possibly poses problems if there is no two pole AFCI available for the panel used. Some AFCI's no longer have GFP component and are able to share a neutral between two AFCI's where ones with GFP component have to be a two pole unit in order to function properly. GFCI requirements also apply anymore and is becoming common to just use dual function breaker on the DW, disposer, or put both on same circuit.
 
Does not fit the requirements for any SABC's if the DW and DSP are fastened in place as is typical.
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See 210.52(B)(1) and (B)(2). The typical fastened in place dishwasher and disposer are not permitted to be on the SABC's. They must be in addition to the required SABC's
 
kwired said:
Does not fit the requirements for any SABC's if the DW and DSP are fastened in place as is typical. A portable dishwasher would be something that could plug into a SABC. Never seen such a thing as a portable disposer but if there were such a thing it could be also I guess.
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My parents had a portable plug in dishwasher.
You and I know that the OP's drawing does not include the 2nd required SABC.

Ron
 
2-pole AFCIs have been variously on and off the market depending on the brand. For example I'm pretty sure that Homeline used to have them but now doesn't, while Siemens was slower to bring them on but now they have them. So unless you always use the same brand they are difficult to plan around. They are also expensive and tie up capital on your shelf if they don't get used because you made a mistake counting your circuits or the client or GC changed the plan on you. It's just another strike against MWBCs, which already require more planning, material management, and knowledge.
 
rc/retired said:
My parents had a portable plug in dishwasher.
You and I know that the OP's drawing does not include the 2nd required SABC.

Ron
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OK, I looked at OP again, it does have a SABC and a DW/disposal circuit involved. For some reason I had it in my mind he had a MWBC with DW on one side and disposal on other side, my bad.
 
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