Flexible Conduit [RE-wrenches]

[Phil Undercuffler]

Mark, 

The thinking behind the metal raceways through the structure, as I've
understood it, is to provide physical protection for the array wiring,
to protect the proverbial remodeling homeowner armed with a sawzall from
cutting into the array feed.  After all, how many of us have turned off
the main breaker and started gleefully hacking into the walls, knowing
we're "safe" from live wires?  While Harry Homeowner may think nothing
of chopping through some random romex, the hope is that he'll think a
bit before whacking through a conduit.  

Worse case, the metal conduit will provide a return current path
(through the sawzall blade) to trip the GFP.

I would have a friendly discussion with your inspector, to see if he
would accept MC Cable as meeting the intent, if not the letter of the
law.  However, you would then need to ensure that your MC Cable fittings
could meet the requirements of 250.97, Bonding for Over 250 Volts.

As far as the 360 rule, MC Cable is a cable assembly, or factory
assembled system of conductors and metal sheathing, while FMC is a
conduit.  Conduits are limited to 360 degrees of bends before passing
through a pull point.  Cable assemblies can be formed into any number of
pretzels (while maintaining a semblance of good workmanship, of course),
as the conductors are integral parts of the assembly.

------------------------------------------------------------

Phil Undercuffler
Technical Services Manager
Conergy, Inc.
1730 Camino Carlos Rey Suite 103
Santa Fe NM 87507 USA
Office | 505.473.3800 x4841
Fax | 505.473.3830
www.conergy.us

------------------------------------------------------------

-----Original Message-----
From: Mark Frye [mailto:markf at berkeleysolar.com] 
Sent: Thursday, May 17, 2007 8:18 PM
To: RE-wrenches at topica.com
Subject: RE: Flexible Conduit [RE-wrenches]


Thanks for the response Erika,

I hope the List does not mind my using some of it's bandwidth to flesh
out
an issue that I am looking at.

After sending the post, I re-visited the Code which makes it clear that
FMC
must have no more 360 degree of bend.

So question answered.  But why is this?  What is the thinking behind the
requirement?

My sense is that FMC is required to allow removal and re-installation of
conductors.  OK, makes sense.

Why is this an issue for me?  Well, NEC 2005 allows un-disconnected PV
DC
conductors to run through a building, but only if in metallic conduit.
OK,
so they can be in FMC, cool, but only 360 degrees.

Well Gee, MC can be bent as much as you like, no limit there under the
Code.
So in some difficult retrofits where even running FMC is prohibitive,
wouldn't it be great to use MC.

Of course the recommendation for the NEC 2008 add MC as an allowable
method,
but it will be more than 6 years before my jurisdiction adopts that.

But in the end, what is the difference between fishing MC around
compared to
pre-loading conductors into FMC and fishing that around.

Just trying to learn a little something and maybe make my job a little
easier.

MPF


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