[RE-wrenches] Protection of Conductors

[Bill Brooks]

Geoff,

SS zip ties are good, but you must be very careful not to pull them tight.
They should only be snug, not tight. These SS zip ties have been shown to
cause ground faults in many cases. Commercial rooftops are accessible, but
not readily accessible. Conductors must be supported properly and protected
from physical damage. The conductors must follow structural members. If they
leave structural members, they must be in a raceway of some kind. A variety
of options there.

Bill.

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Geoff
Greenfield
Sent: Friday, October 03, 2008 7:19 AM
To: RE-wrenches
Cc: Randy; Kent Phillips
Subject: [RE-wrenches] Protection of Conductors

Hey wrenchers... we have an internal debate going about a code section
interpretation... "subject to physical damage".  Code compliance is a must,
best practice is an expectation (...weighed against material and labor cost
(prevailing wage job)). 

Application is a flat roof with no public access (locked hatch).  We are
using DP+W "Power-tube" flat roofing system for the first time... the
question is how to deal with the inter-row N-S wire runs... about 100 gaps
about 24" between the E-W rows of panels.  There are plenty of 2"x2" strut
members running under the array N-S. We will "exit" the array field in
ridgid conduit to combiner boxes.

The flat roof system we usually use has built in wire trays... using this
new system has brought up this question... Our options include dressing the
XLP bundles with SS zip ties alongside the N-S struts, or using Galv. RMC,
strapped, with bushings (or S-80 PVC) at all these walkways... or using
Unistrut (w/cap) as a lay in wireway (to speed up labor (debatable)).

Below are some of the code references... the basic question seems to be:
does the limited access of this roof keep us out of "subject to physical
damage"?  What is a "Readily accessible location?"

Thanks everyone.

For a brighter energy future,

Geoff Greenfield
President
Third Sun Solar & Wind Power Ltd.
340 West State Street, Unit 25
Athens, OH 45701

740.597.3111     Fax 740.597.1548
www.Third-Sun.com

Clean Energy - Expertly Installed


> 
> Next, one might argue, I suppose, that the racking system itself, acts
> as
> protection and that the conductors should therefore, not be considered
> to
> be exposed.  I disagree based on NEC definition.  That stated, I
> would
> consider these NEC references for more perspective:
> 
> Pretty straightforward NEC 100 Definitions Exposed (as applied to
> wiring
> methods):  On or attached to the surface...  
> 
> NEC 300.4 gives various cases for protection against physical damage
> requirements.  Long article.  Worth a read.  Does not address our
> exact
> case, but I would say that the following methods would be appropriate
> based on similar cases...    
> 
> NEC 344.10 (A)(1) Galvanized steel and stainless steel RMC.  ...shall
> be
> permitted under all atmospheric conditions and occupancies. 
> 
> NEC 352.10(f) Exposed. PVC conduit shall be permitted for exposed
> work.
> PVC conduit used exposed in areas of physical damage shall be
> identified
> for the use.  FPN:  PVC conduit, Type Schedule 80, is identified for
> areas
> of physical damage. 
> 
> Also,
> 
> NEC 690.31(A) ...Where photovoltaic source and output circuits
> operating
> at maximum system voltages greater than 30 volts are installed in
> readily
> accesible locations, circuit conductors shall be installed in a
> raceway.
> 
> One might argue, then, why don't the module interconnects have to be
> protected, also...
> 
> NEC 690.31(B) is really the key to all of this:  Single-Conductor
> Cable.
> Single-conductor cable type USE-2, and single-conductor cable listed
> and
> labeled as photovoltaic (PV) wire shall be permitted in exposed
> outdoor
> locations in photovoltaic source circuits FOR PHOTOVOLTAIC MODULE
> INTERCONNECTIONS within the photovoltaic array.  
> 
> So, I suppose that if our source circuit interconnections extend from
> row
> to row, then we can leave those exposed.  I don't like it, but it
> would
> probably have to be accepted.    
> 
>
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