I think that article is a bit biased, when you take into consideration Square D has yet to market a 2-pole combination AFCI breaker. They are trying to "downsale" a MWBC because those that want to use MWBC's will not buy their loadcenters.
that's a good point. but it begs the question, how often are two-pole AFCIs utilized? typical households run predominantly single pole loads, with maybe a handful 2-pole (an over for example). i did try to contact square d as to why they have not introduced 2-pole AFCIs, but have not heard back. their website did state that they are potentially looking at this option, given today's electrical needs and capabilities.
Additionally, that article presents disadvantages fairly accurate, but does leave out an advantage of a MWBC... which is for balanced MWBC's, the I?R heat losses are reduced, saving the consumer money. Of course that is when operating nominally. Also on this matter, the article points out the disadvantage when an open neutral occurs. I believe it to be an exaggeration. Seriously, how often does that happen compared to operating nominally? Seems to me it happens most when an unqualified person disconnects a splice while the MWBC is energized than it does from a bona fide open-neutral fault.
true as well, but it only takes one time to cause a problem. i have read many blogs/posts that seem to highlight problems people have encountered with 2-pole AFCIs, with the issue that a shared neutral can be the root cause. Also, according to this gentlemen's post, his electrician installed 12/3 in a single phase application. heck, why not run single conductor cable, like you would for typical 120V lighting. multi-wire cable seems slightly impractical in my mind.
Granted I don't know the loads for certain, but if you spare out one ungrounded conductor, you'd have to track down the loads it serves and switch them over to the not-spared conductor. Additionally, you could easily manage to overload the circuit in doing so, unless you track down and calculate all effected loads. And if the circuit could then easily become overloaded, the only other option is to pull a new circuit... which I believe is the last practical option from the homeowner's perspective.
you would still have to test the conductivity of the circuit, before connecting any loads, or even at the panel. i have been to job sites where 120V UPS power would be required, but loads and length between source and load, are large enough that upsizing to #10 or even #8 is required, and at that point, the odds of purchasing 10/2 & 8/2 cable is rare and expensive; thus we would spare out the cable. of course, UPS wouldn't be found in households, but can be a viable alternative, to avoid purchasing brand new equipment to meet deadlines. if the cable's pulled, and the panels purchased, you simply tape both ends to signify which ungrounded conducter is which, on both ends of the circuit, before terminating the cable. cable numbering being marked onto the cable, is another method as well.
i'm not sure where this gentlmen is, in regards to his installation and startup, so this was just a thought on the matter, to help before final testing and power up is completed.
thanks, smart, for the comments.
