[RE-wrenches] FMC vs MC Cable

[Kirk Herander, VSE]

Our local inspector defines metallic raceway as metal conduit without
preassembled conductors, such as FMC (greenfield) or EMT. MC is a cable
assembly and only allowed from the first point of disconnect onward.

Kirk Herander
Vermont Solar Engineering
802.863.1202
fax 802.863-7908
NABCEP(tm) Certified Solar PV Installer
Xantrex Certified Dealer Charter Member
NYSERDA-eligible installer
VT Solar Incentive Program Partner

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Hans
Frederickson
Sent: Monday, October 27, 2008 1:54 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] FMC vs MC Cable

I have seen MC cable used for DC circuits and I don't think it meets the
requirements of 690.31(E) for a metallic raceway. I don't think the metal
cladding on MC cable qualifies as a raceway any more than the plastic
sheathing on romex does, but I've heard differing opinions on this. Last I
checked the code process on www.solarabcs.org, there was some discussion on
clarifying this point for the 2011 NEC, with some arguing for and some
against specifically allowing MC cable.

Obviously, MC cable is much easier and faster to install, but I don't think
it meets the intent of 690.31(E). My understanding is that firefighters wish
to have some protection from DC circuits when they're penetrating a
building. We should also concerned about anyone cutting into a wall or
ceiling during remodeling, etc. Flexible metal conduit is heavier duty than
the cladding on MC cable, and would hold up better against a cutting tool,
but FMC is not a good choice for long runs because the friction makes
pulling the wire a challenge. It's also very expensive. For our residential
new construction pre-wires, we install 3/4" EMT conduit. It takes quite a
bit longer (and more skill) than MC, but allows more flexibility in the
number of circuits used, and will be safe from any tightening in the code
down the line.

Regards,
-Hans


Hans Frederickson
Estimator / Project Manager
Frederickson Electric, Inc.
(360) 385-1395
www.fredelectric.com



-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Monday, October 27, 2008 10:08 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] FMC vs MC Cable

On new construction, we like to run MC cable throughout  the building shell,
from the PV modules to the inverter. We of course include a properly rated
DC disconnect before or just after penetrating the shell and use protection
plates when we run through studs. And we probably will need to add labels
soon in many jurisdictions. My question is as follows:

What are the implications of using flexible metal conduit and pulling the
wires ourselves vs using the pre-wired MC cable? Both jackets are Al.

- Peter

Peter T. Parrish, California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 CA Lic. 854779,
NABCEP Cert. 031806-26 peter.parrish at calsolareng.com 



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