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

Wed Dec 9 13:55:39 PST 2015

Now that I am teaching electrical/solar more than installing electrical/solar I am designing labs and systems for education.  As part of my classes I spend lots of time discussing wire management and "safe and workman like manner" to students with little to no experience in electrical systems. Even these students can see the problems with PV wires flung on a roof with little to no support. So I've taken a lead from William and I have started installing all of our lab systems with cable management like William has shown.  We used PVC to support the trunk cables for our enphase pole mount and we use it on both of our training roofs. I hope these lessons stay with the students when they leave here and enter the workforce. 

Jesse Dahl

NABCEP PV Installation Professional
IBEW Local 292 - Electrician 
Electrical/Solar PV Instructor - HCC

Sent from my iPhone

> On Dec 9, 2015, at 2:30 PM, William Miller <william at millersolar.com> wrote:
> 
> 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
>  
> <image004.jpg>
> Lic 773985
> 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
>     
> 
>  
> 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
>  
>  
> <image003.jpg>
> Lic 773985
> millersolar.com
> 805-438-5600
>  
> From: RE-wrenches [mailto: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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