MWBC with AFCI

darekelec said:
if it says on a afci or gfci 2 pole breaker 'to be used on 120/240V circuits' can I use it on 120/208V single phase circuits? in NYC we only have 120/208 single phase for residential.
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At one time I don't believe most AFCI were compatible with 208 volts and MWBC's. I don't know if that is still an issue or not, or which manufacturers it may or may not apply to.

GFCI protection only shouldn't have any problem with this though, all it is looking for is net zero on all protected conductors, what current goes out on one conductor has to return on any other protected conductor of the circuit. So as long as nothing finds a return path that is not through the GFCI it will hold.
 
Quick search and it appears that Siemens, Square D Qo & HOM, Leviton and Eaton BR have 2 pole afci breakers for use on MWBC. Can't speak to how well they all perform but I have had good outcome with the Siemens 2 pole afci breakers. They also were the first to make a 2 pole afci that worked for MWBC, They also have a tandem AFCI. The new Siemens don't even need the load neutral brought to the breaker. Both the PON and pigtail neutral only are present for the electronics of the breaker.
 
The two-pole AFCI breakers (Siemens at least) are pretty expensive, well over $100. Not that much more than two single-pole ones though, I suppose.
 
Fred B said:
Quick search and it appears that Siemens, Square D Qo & HOM, Leviton and Eaton BR have 2 pole afci breakers for use on MWBC. Can't speak to how well they all perform but I have had good outcome with the Siemens 2 pole afci breakers. They also were the first to make a 2 pole afci that worked for MWBC, They also have a tandem AFCI. The new Siemens don't even need the load neutral brought to the breaker. Both the PON and pigtail neutral only are present for the electronics of the breaker.
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I never have a issue with two pole afci breakers , don’t get me wrong I don’t use them often but I do, and at least 7-8 years ago prob more GE designed their CAFCI breakers with no gfp to function using a shared neutral to accommodate MWBC’s, eventually Siemens followed GE’s lead removing GFP from their CAFCI breakers , I can verify two single pole PON Siemens CAFCI breakers with a identified handle tie functions without issue when protecting a 120/240 MWBC, I’ve never attempted with the older Siemens or Siemens with a pigtail
Heres a link for GE
 
I have used ge single pole afci's for a multiwire branch circuit. The neutral from the load goes to one breaker the other is left open.
 
Fred B said:
Quick search and it appears that Siemens, Square D Qo & HOM, Leviton and Eaton BR have 2 pole afci breakers for use on MWBC. Can't speak to how well they all perform but I have had good outcome with the Siemens 2 pole afci breakers. They also were the first to make a 2 pole afci that worked for MWBC, They also have a tandem AFCI. The new Siemens don't even need the load neutral brought to the breaker. Both the PON and pigtail neutral only are present for the electronics of the breaker.
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The question was will they work on a 208/120 MWBC. I don't think some of them worked on this system because the phase angle caused issues with how they operate. They worked fine on 120/240 MWBC's though.

I myself never used a 2 pole AFCI or handle tied two that were capable of operating that way, and only occasionally have come behind someone else that utilized those.
 
I can see some these newer AFCI's from the ones that don't even require landing the load neutral on the breaker not having a problem with MWBC on a 208 supply. They basically are only monitoring activity on the ungrounded conductor and are otherwise two independent breakers.
 
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