[RE-wrenches] AC & DC in Raceway

[Hans Frederickson]

I am not aware of any type of installation where the NEC would require
bundling in a gutter. I have seen some non-metallic raceways with built-in
partitions for low-voltage and line-voltage wiring, but of course this type
of product wouldn't be applicable for the AC/DC separation you're looking
for. Anyway, you should be careful with bundling, because although it makes
for a neat installation, your AHJ might consider tightly grouped conductors
in a gutter as requiring derating, as if they were sharing a raceway.
Typically this would not be an issue for solar installations, since we're
increasing wire sizes over minimum requirements in order to minimize voltage
drop / wire resistance losses, but if you had say, five strings, and you
bundled the 10 DC wires together for a distance of 24" or more, your
derating factor may have just hit 50%, and that's in addition to any
derating that might be required by ambient temperature. Just keep in mind
that any current carrying conductors that are bunched together with zip ties
just might run a bit warmer and thereby have increased resistance. I heard a
story somewhere once about a homeowner who thought it would be very
workmanlike to _braid_ all the home runs together as they left the service
panel. According to the story, the AHJ took a dim view of this and wrote an
ampacity correction based on NEC 310.15(B)(2) "Adjustment Factors for More
Than Three Current-Carrying Conductors in a Raceway of Cable". This makes
sense when you consider that the braided romex was essentially one big
cable.

-Hans

Hans Frederickson
Project Manager
Frederickson Electric, Inc.
www.fredelectric.com
 

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Drake
Chamberlin
Sent: Thursday, September 24, 2009 2:19 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] AC & DC in Raceway


Bundling is a good idea, I to that too.  But where does it say we have to do
it?

At 09:43 AM 9/24/2009, you wrote:


	Nik, we always use 4x4 gutters when ever possible - keeps things
clean and neat - as long as insulation voltage rating is same on all wires
and wires are bundled (AC and DC - tie wraps or tape) and it's all from the
same system (house wiring is another system) then it's OK.......
	
	Max Balchowsky 
	SEE Systems
	
	
	From: "Nicholas Ponzio, Building Energy"
<nponzio at buildingenergyus.com>
	To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
	Sent: Thursday, September 24, 2009 4:02:21 AM
	Subject: [RE-wrenches] AC & DC in Raceway
	
	Wrenchers,
	
	What's the deal with mixing AC and DC conductors in a raceway? The
job in question has a 6x6 wireway under the inverters. Conductors will have
their own conduits but is it ok for them to share the wireway?
	
	Thanks in advance for clarification on this,
	Nik
	 
	
	--
	Nicholas Ponzio
	Building Energy
	1570 South Brownell Road
	Williston, VT 05495
	
	t: 802-859-3384 x15
	f: 802-658-3982
	www.BuildingEnergyVT.com
	
	"Building Solutions for a Sustainable Future"
	
	
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM  Certified PV Installer 
Office - 740-448-7328
Mobile - 740-856-9648