Ac faults and Multi-wire branch circs [RE-wrenches]

[Bob-O Schultze, Electron Connection]

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Goeff,
scary, ain't it. After the first time I saw a WHOLE panel full of  
that in So. OR, I started counting neutrals EVERY TIME. If neutrals  
don't equal single pole hots, watch out!
cheers, Bob-O
On Dec 22, 2005, at 9:29 AM, Geoff Greenfield wrote:
>
> I just left a job where I pulled a number of circuits to a backed  
> up sub
> panel - including a C-H arc fault breaker.  Didn't try the self  
> test (it was
> an OB-VFX-3548) - will have the customer try it just for info.
>
> On another note, I discovered my first field sighting of the elusive
> "multi-wire branch circuits".  Perhaps copper prices or the hype cost
> sensitive builder and EC are the driver, but the panel was full of  
> 'em!  I
> had nary a thought to them during design phase, other than putting  
> a sticker
> on the (jumper-converted to 120) sub-panel warning "no multi wires  
> etc".
>
> So there I was, hours from home, an excited customer waiting for their
> system, and the goal of throwing the switch ON SOLSICE DAY!!!! (and  
> then
> high tailing it out of there with a check in my pocket and a big
> potluck/solstice bonfire on the schedule for me and the installer I  
> was with
> and our families).  And 1/2 the "backed up loads" on this grid  
> present but
> not net metered HBX (LBX?) style PV system turn out to be on leg 2  
> of MWBCs!
>
> Field design change work around to the rescue... Plan A called for
> everything to be 120, including a jumpered sub panel, with  a  
> single 240 VAC
> soft start well pump pulled off a dedicated X-240 in the PS2AC (I  
> was even
> going to wire the X-former downhill from the pressure switch).  Plan B
> changed to a 240 VAC x-fer switch, the sub-panel maintaining L1/L2  
> isolation
> on the multi wires (and stacking everything else on L1), and  
> accepting the
> small losses of the x-240 being in several more circuits and being  
> hot all
> the time.  I got the advantage of being able to X-fer the well pump  
> with all
> the other loads (VS not being able to isolate the well pump from  
> the X-240)
> plus throwing the switch on Solstice and making it to the party on  
> time!
>
> So - I think I did it all the right way - everything worked and the  
> x-240
> breakers didn't trip-  In checking things out before power up I got  
> really
> confused about impossible 120 VAC on L2 even with the X-former off  
> line (but
> no 240 across legs).  Still not sure what I was reading - concluded  
> that it
> must have been from the mechanical kwh meters I had in the circuits  
> (wired
> 240 "normal" style)
>
> So watch out, we may be seeing more multi-wire circuits!  And on  
> the day
> after the solstice, as we have a little more light in the day and a  
> glimmer
> of the return to warmer days, take the time to think about the Sun,  
> the
> source of all of our energy (and most of OUR livelihoods), and it's  
> role in
> our history and future.  Keep up the good work Brothers and  
> Sisters!  In
> light of the "debate" about saying "Merry Christmas" VS "Happy  
> Holidays",
> this born again pagan will take an opportunity to answer either  
> well wisher
> with a proud "Happy Solstice to all"!
>
> For a brighter energy future,
>
> Geoff Greenfield
> NABCEP Certified Energy Practitioner


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