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

[Geoff Greenfield]

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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

THIRD SUN SOLAR & WIND POWER Ltd.
340 West State Street
Athens, OH 45701

www.third-sun.com
(740) 597-3111

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