[RE-wrenches] Secure/support PV wire requirements?

Wed Dec 9 12:30:11 PST 2015

Ben:

Yes, we do use this technique on roof mount systems as well.  This is true
for micro-inverters and string inverters alike.  The PVC holds trunk cables
and DC cables alike.

The attention we pay to detail does add to the cost of our jobs.  The
development time adds to the production costs.  The Holy Grail is to
develop processes that are quick, efficient and use off-the-shelf
components.

You know what 1-1/2” PVC costs.  We can mill 500 feet of conduit in an
hour, enough for 150 modules.  One person can do it safely, two is
quicker.  Development is again crucial—we built a jig that guides the
conduit and cuts the slot in one pass.  Add stainless cable ties and the
total material costs is about $2.50 per module.  The clips are made from
the conduit scraps.  The slot is widened with PVC cutters and they clip
right on.  This is a very solid method.

Sure the cost adds to the bottom line, and sure we lose some jobs due to
higher costs.  The decision to do what I do is a personal, ethical
decision.  I have a deep sense of satisfaction in a job well done and in
occupying my mind and hands improving my craft.  Marketing is key.  Not
everyone can afford a Mercedes but some can.  I need to convince potential
clients of the difference between brand Miller and the rest.

I see the problem as a failure of regulators to insist on safe practices
on-par with other branches of the electrical industry (try running
unprotected wires to an air-conditioning unit and see if you get away with
it). The good news:  the situation is gradually improving.

Thanks for asking.  These problems and solutions are of great intrigue to
me.  I hope others on this list are willing to improve their techniques and
that I can help in some way.

Sincerely,

William Miller

By the way, Bill Brooks wrote an article addressing the specific of USE and
PV cable management.  I can’t lay my hands on a copy but if anyone is
interested and can’t find a copy on-line I will look further in my files.

Wm

[image: Gradient Cap_mini]
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
Behalf Of *Benn Kilburn
*Sent:* Wednesday, December 09, 2015 11:57 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Secure/support PV wire requirements?

William,

Are you using this method on roof top systems that are parallel to the roof
as well?

I don't want to bring up the question of what cost this adds to the job....
but here i am bringing it up!
(labour and material, ...measuring & cutting pipe to length, cutting slots
and "clips" on table saw, filing cut pipe edges, attaching to rails...)
There is no doubt that your method shows attention to quality and
workmanship however the solar biz is quite competitive and making the
decision to use this method and its added costs would surely cost us jobs.
I'm going to assume that you have been able to standardize and refine this
method to reduce time and costs?

All,
I prefer to keep an assortment of wire management solutions handy on the
roof when we are supporting PV and/or micro-inverter wires....those being;
thick nylon cable ties *MUST HAVE metal tooth, NOT plastic tooth* (T&B
TY27MX), stainless steel cable ties, and a couple different types of PV
cable clips (heyco) that attach to the rail or module frame.

Assuming a typical house (shingle) roof top system where bottom of the mod
frame rests +-4-6" off the roof surface....
If it is a single row of mods with the j-boxes on the high side, then
securing the PV wires can usually be done after the mods are mounted and
can be done quite well with 2-4 metal PV cable clips attached to the
modules upper frame. Securing the PV cable to the mod frame within 12" can
be done and if not then let your professional judgement guide you that it
is secure and protected from coming loose and subject to potential damage
from contact with the roof or anything else.

If it is two rows of mods, one above the other, with the mod j-boxes
meeting in the middle (perhaps sharing microinverters mounted along the
middle rails)..... or any other combination of module layout, MC wire leads
or microinverter orientation... yes, it can become cumbersome at times to
find appropriate attachment points to secure wires... and it would be to
time consuming and confusing to discuss the array of possibilities here...
so again, you need to rely on your professional judgement to use the proper
material and methods to secure any and all wires.
This is not a task to be given to someone without an eye for detail and
workmanship.

*Benn Kilburn *

CSA Certified Solar Photovoltaic Systems Electrician, SkyFire Energy Inc

6706 – 82 Ave NW | Edmonton, AB | T6B 0E7

P: 780-474-8992 | F: 888-405-5843 | www.skyfireenergy.com

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On Wed, Dec 9, 2015 at 11:33 AM, William Miller <william at millersolar.com>
wrote:

Rebekah:

What you desire to do is not impossible.  Most module manufacturers specify
supports approximately 20% form each short side.  For a 66 inch module this
is 13.2 inches.  If you attach the factory PV leads to the rail, you are
close to the 12 inch requirement.  If you reduce the offset to an actual
12” you are at 18% of the module width. Either way, I suggest it is close
enough.

How to secure the leads?  Well there are “UV resistant” wire ties, but the
lack of longevity of these is starting to be realized.  There are other
clips or metal reinforced ties that may be adequate.   Clips we tried are
loose and/or flimsy.

We have been experimenting with various procedures for over a decade.  Our
best method so far is to slot PVC pipe and ley the leads inside.  We do
this on the table saw using dual blades.  The cut is sharp and needs to be
deburred.  Once we lay the leads in we secure them with a clip made form a
short section of the same slotted pie.  We cut short lengths of the same
slotted pipe (3”), expand the slot using PVC cutters and it clips securely
over the long sections of PVC.  See attached.

William

[image: Gradient Cap_mini]
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org
<re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of *Rebekah Hren
*Sent:* Wednesday, December 09, 2015 6:06 AM
*To:* RE-wrenches
*Subject:* [RE-wrenches] Secure/support PV wire requirements?

Hi,

Wondering if anyone has insight into Code requirements for
securing/supporting PV wire behind the modules?

I am aware that USE-2 sends you to Section 334.30 requirements for Type NM
(12" from box, every 4.5 ').

However, I think this is totally bogus, for 2 reasons.

1) Section 338.10(B)(4)(b) that refers the NM article is titled "Branch
circuits or Feeders."  These are PV source and output circuits, not branch
circuits or feeders.

2) it is nearly IMPOSSIBLE to secure the PV wire within 12" of the module
junction box for many modules, especially in landscape wiring, without
causing more harm than good, too tight a bending radius, stress on
conductors.

334.40(B) maybe leaves a little wiggle room for concealed spaces in
structures where it is impracticable to support.

My big problem here is that both requirements of 334.30 are useless or
harmful to PV systems. 12" to the box is often impossible, and 4.5" feet is
too long to go without any support behind the array!!! I just noticed there
was a proposal in 2017 to Codify the 334.40 requirements for PV cables and
so I guess I only have myself to blame for not writing a better proposal at
this point.

Rebekah

-- 

Tel: 336.266.8800
NABCEP Certified Solar PV Installation Professional™ 091209-85
NC Licensed Electrical Contractor

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