Dave,
You are on to something that has been on my mind for years. I believe
that FMC inside the building before a disconnect with DC conductors
above 250V is allowed by the Code.
And I believe the requirement for bonding in 250 applies regardless of
whether or not a separate EGC is run in the FMC.
The real problem I faced was getting FMC and fittings rated for the job.
FMC is available in both Al and steel, thin wall and normal. I always
used thick wall steel FMC and fittings that had a set screw clamping
mechanism for attaching the adapter to the FMC. I spent time trying to
find materials with listing for the purpose but never got to the bottom
if it.
I have always had a problem when I saw thin wall AL flex being used with
twist-in-insert type fittings.
Mark Frye
On 11/9/2012 5:44 AM, Dave Click wrote:
Nick, what the AHJ is telling you may actually be in reference to
250.97; for most PV output circuits (yes these are necessarily dc)
this bonding requirement applies since array VOC > 250 VDC. As Kent
just pointed out, these dc conductors clearly don't meet the NEC
definition of a service.
"250.97 Bonding for Over 250 Volts. For circuits of over 250 volts to
ground, the electrical continuity of metal raceways and cables with
metal sheaths that contain any conductor other than service conductors
shall be ensured by one or more of the methods specified for services
in 250.92(B), except for (B)(1)..." followed by an exception.
Seems that FMC is OK as an EGC if your conductors have <20A OCPDs,
which I imagine you do, but that FMC also can't be longer than 6' (see
250.118(5)). So I think your AHJ is probably right and I just learned
something. If you're running a separate EGC anyway, you may want to
ask why this bonding business is so important-- but I don't have an
NEC reference on this to help you argue this. Maybe the AHJ would
allow you to just run MC cable as the 2011 NEC allows.
John Wiles is awesome. Someone on this list had to say it.
DKC
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