[RE-wrenches] Cable tray

Bill Hoffer sunengser at gmail.com
Fri Mar 29 09:23:45 PDT 2013


Re-Wrenches

I have done numerous Mountaintop telecommunication PV systems, and they use
outdoor rated cabling in cable trays extensively on their towers into their
control rooms.  If it can survive the UV, snow wind and ice rime buildup
there I am sure it can handle many of the roof top locations easily.  I am
guessing that they may have used conduit in the early days, but found it
more cost effective and less maintenance in the long run to run cable tray.
  The only real difference might be the exposure to heat on a roof, which
should be better in open cable tray than stuffed in a conduit!  There is a
real advantage to being able to visually inspect and replace damaged wires
easily before a potential fault occurs or for that matter to track down and
isolate a fault.   Europeans think that we are crazy putting conductors in
metal conduit and prefer to use outdoor rated conductors where they are
separated by air to reduce potential for faults across current carrying
wire and being able to visually inspect for damage to the conductors.
Conduit bending is a true art that many electricians pride themselves in,
so I can see they reluctance to change, but there is certainly enough
evidence that cable trays and outdoor rated wires are a good idea from
around the world and the telecommunications industry.  We should learn from
the Europeans and Telecommunication industires, who by the way have less
problems with faults and much lower installation costs!

Bill

On Fri, Mar 29, 2013 at 3:41 AM, Bill Loesch <solar1online at charter.net>wrote:

>
> Hi Chris,
>
> Thanks for a glimpse of how our German brethren handle PV design &
> installation. After all, who has more experience with design, execution,
> and funding than the Germans? There remains an arrogance that the US has a
> lock on how best to do any number of things. Hopefully, this antiquated
> attitude will change, soon; hopefully, before we are all reduced to asking
> the equivalent of, "Would you like to Supersize that meal?"
>
> Best wishes on your install. Please keep us informed of how others around
> the world better handle these items.
>
> Bill Loesch
> Solar 1 - Saint Louis Solar
>
> On 28-Mar-13 1:03 PM, Chris Mason wrote:
>
> I am working on a large installation in a country that uses 230/400V 60Hz
> for the grid, so we had to look to Europe for the inverters and work 1000V.
> I spent some time on the phone with SMA Germany to discuss the
> reqiurements in Germany and to understand the design methodology the
> inverters were designed for.
> First of all, the inverters are gorgeous. The first one we installed is a
> 3Ph 17KW with 6 sets string inputs, 2 x MPPT. They connect the strings
> directly to the inverters, no disconnects. The inverters have a Electronic
> Solar Switch on the bottom, pull it down and the strings are disconnected.
> We are using 26 module strings or that install, which massively reduces
> cabling and components.
> I showed the engineer a photo of our larger installs, he laughed at the
> use of "pipes" for the cables.
> We install massive AC disconnects, they use a little isolator about the
> size of a Coke can.
> Everything is a multi-core cable.
>
>  I also read a guide to the British Standards on PV installation, and
> their approach to grounding is absolutely different.
> Since PV conductors are all isolated now, they don't even want you to
> ground the array structures, in fact they describe grounding as a shock
> hazard. Very different mentality.
>
> I might think that the US way is likely safer if we were comparing with
> China or the third world, but this is Germany. I think they know
> electricity.
>
>  Chris
>
>
> On Wed, Mar 27, 2013 at 12:16 PM, John Berdner <John.Berdner at solaredge.com
> > wrote:
>
>>   Exposed single conductor sunlight resistant cable in cable trays are
>> widely used in PV systems outside the US.
>>
>> There is a very large installed base of systems with good long term
>> performance data using this type of construction.
>>
>> We should not discount the advantages of wire cable trays just because we
>> are unfamiliar with it.
>>
>>
>>
>> Look at data cabling – Characterized by many, relatively small, cables
>> over long distances with periodic drops.
>>
>> Sounds a lot like PV source circuits (other than voltage and current in
>> the wires of course).
>>
>> There are lots of videos out there showing how to pull 10’s of pairs of
>> wires simultaneously in cable trays.
>>
>> IMHO, we need to look at ideas like this to reduce installation cost and
>> time.
>>
>>
>>
>> Installation costs are becoming the tall pole in the tent and new
>> thinking is needed.
>>
>> As systems are falling to sub $3.00 /Watt all-in, running wire in conduit
>> will simply not be cost effective.
>>
>> Running wire in conduit is one of the reasons PV installation costs in
>> the US are double (or more) of those in Europe.
>>
>> As one of my former German colleagues noted:
>>
>> “It is only in the US where you need first to be a plumber before you can
>> be an electrician”
>>
>>
>>
>> Best Regards,
>>
>>
>>
>> John Berdner
>>
>> General Manager, North America
>>
>>
>>
>> SolarEdge Technologies, Inc.
>>
>> 3347 Gateway Boulevard, Fremont CA 94538 USA  *(*Please note of our new
>> address.)*
>> T: 510.498.3200, X 747 <510.498.3200%2C%20X%20747>
>>
>> M: 530.277.4894
>>
>>
>>
>> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
>> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Allan Sindelar
>> *Sent:* Wednesday, March 27, 2013 8:51 AM
>>
>> *To:* RE-wrenches
>> *Subject:* Re: [RE-wrenches] Cable tray
>>
>>
>>
>> Andrew,
>> We have used #10 USE-2 for about 16 years, and our high-elevation New
>> Mexico sun is quite intense. I have yet to see any degradation exceeding
>> fading discoloration on any conductors from that far back, even when
>> directly exposed to sunlight. No cracking, peeling, delaminating, or
>> hardening.
>> Allan
>>
>> *Allan Sindelar*
>> Allan at positiveenergysolar.com
>> NABCEP Certified Photovoltaic Installer
>> NABCEP Certified Technical Sales Professional
>> New Mexico EE98J Journeyman Electrician
>> Founder and Chief Technology Officer
>> *Positive Energy, Inc.*
>> 3209 Richards Lane (note new address)
>> Santa Fe, New Mexico 87507
>> *505 424-1112 <505%20424-1112>*
>> www.positiveenergysolar.com
>>
>>
>>
>>
>>
>> On 3/27/2013 8:41 AM, Andrew Truitt wrote:
>>
>>  Bill - What is your take in conductor insulation degradation over time
>> when exposed to UV? Regardless of the "sunlight resistant" labeling, USE-2
>> (and I assume PV wire though I haven't seen it yet) does show wear after
>> years of exposure to direct sunlight.  Maybe best practice would be to use
>> cable trays where conductors are shaded and [properly installed] conduit
>> when exposed to direct UV?
>>
>>
>>
>> - Andrew Truitt
>>
>>
>>
>> Sent from my iPad
>>
>>
>> On Mar 26, 2013, at 11:55 PM, "Bill Brooks" <billbrooks7 at yahoo.com>
>> wrote:
>>
>>  William,
>>
>>
>>
>> I have all the respect in the world for you, but I’m not referring to
>> “basket tray”, which is only appropriate for small conductors. I’m talking
>> about legitimate cable tray that can be up to 12” wide and that has a top
>> and rungs every 12”. The main facilities that use it in the United States
>> are large industrial facilities. Most electricians don’t get to work with
>> it. It is clearly superior to EMT and is at least as good as IMC without
>> all the hassle of threaded fittings and setting up expansion joints and
>> worrying about 20 years of conductors thermal cycling. Even the best
>> electricians have problems with this stuff.
>>
>>
>>
>> I am talking about projects with 800 foot long feeder runs. We can bring
>> them in the building and build a rack for the conduit or run covered tray
>> outside. As the 2014 NEC will require, you will have to use contactor
>> combiners or some other means to shut down the conductors inside a
>> building. It’s all doable. My recommendation after seeing the aftermath of
>> rooftop conduit by good electricians is to put cable tray on roofs and use
>> conduit if you bring the feeders indoors. It will become common practice
>> soon. Hopefully sooner than later.
>>
>>
>>
>> Bill.
>>
>>
>>
>> *From:* re-wrenches-bounces at lists.re-wrenches.org [
>> mailto:re-wrenches-bounces at lists.re-wrenches.org<re-wrenches-bounces at lists.re-wrenches.org>]
>> *On Behalf Of *William Miller
>> *Sent:* Tuesday, March 26, 2013 9:49 PM
>> *To:* RE-wrenches
>> *Subject:* Re: [RE-wrenches] Cable tray
>>
>>
>>
>> Bill:
>>
>> I have to disagree with you on this one.  We can not abandoned a tried
>> and true practice just because some practitioners don't do it right.  I
>> don't know how one can justify saying that encapsulating high voltage
>> conductors in a conduit is less safe than exposed in a flimsy basket.
>> Consider snow and ice and falling objects.
>>
>> Too many installers entered the PV field without first acquiring the
>> necessary skills as journeymen or women electricians.  I don't see the
>> benefit of rewriting the code to accommodate a lack of skills in the
>> industry.
>>
>> Respectfully,
>>
>> William Miller
>>
>> PS:  The temperature adders always encourage us to enter the building
>> envelope at the first appropriate location to avoid adding them.
>> Thoughtful installers will do the same.
>>
>> Wm
>>
>>
>> At 10:15 PM 3/25/2013, you wrote:
>>
>>
>>  Content-Type: multipart/alternative;
>>         boundary="----=_NextPart_000_00E3_01CE29A6.37CC5110"
>> Content-Language: en-us
>>
>> William,
>>
>> I would strongly disagree that conduit is tried and true on rooftops. I
>> have rarely seen good conduit runs on rooftops. Most electricians have no
>> clue how to work with expansion joints. Conduit on rooftops is a bad idea
>> in general. Most conduit runs in big buildings are all done indoors for
>> good reason. We are the crazy people doing things on the roof.
>>
>> The sooner we get away from conduit­particularly for long feeder runs­the
>> better.
>>
>> In Europe they don’t have problems with their rooftop wiring systems
>> because everything is in tray.
>>
>> For those that don’t allow cable tray for anything less than 1/0, just
>> remember that if it isn’t called cable tray, then 392 doesn’t apply. The
>> NEC would allow us to use treated lumber in place of cable tray. This makes
>> no sense.
>>
>> We did some research on the origin of the 1/0 requirement, and it is
>> ancient and no longer relevant. Just because it is in the code, does not
>> mean it is correct. That’s why we try to fix it every three years.
>>
>> Bill.
>>
>>
>>
>>
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>
>
>  --
> Chris Mason
> President, Comet Systems Ltd
> www.cometenergysystems.com
>  Cell: 264.235.5670
> Skype: netconcepts
>
>
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-- 
Bill Hoffer PE
NABCEP Certified Solar PV Installer™
Sunergy Engineering Services PLLC
2504 Columbia Ave NW
East Wenatchee WA 98802-3941
bhoffer at sunergyengineeringservices.com Cell:(509)679-6165
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