[RE-wrenches] Cable tray

Thu Mar 28 11:03:46 PDT 2013

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****
>
> 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*
> 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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