[RE-wrenches] EMT in attic

[Mark Frye]

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