Friends:
The information from the manufacturer seems entirely untrustworthy for these reasons: 1. The representative is mis-informed about the prevalence of stranding of THHN. 2. It is my understanding the all THHN on the market is now THWN so this designation should be used (I am ready to be corrected on this point as my information is anecdotal). 3. The representative focuses on the sealing of the gland portion of the cable on the THWN insulation which ignores the existence of bulkhead mount MC connectors (I think the nomenclature in the manufacturer’s brochure is “receptacle”). If you are using a bulkhead connector the gland does not exist and any discussion of said gland is therefore irrelevant. When I observe the conductor in a 10 AWG building wire and the conductor in a 10 AWG PV wire I detect absolutely no difference. I firmly believe that you can wire-nut PV wire to building wire in a weatherproof junction box. Gland connectors (by Heyco and others) are readily available so one can run PV wire in a box, strip and connect. Keep in mind weatherproof boxes are hard to hermetically seal so a weep hole in a low point keeps them from filling with rain water or condensate. Weep holes are specifically allowed in the NEC. I detect no difference when observing an MC pin crimped on both PV wire or THWN. See this link <https://millersolar.com/MillerSolar/practices/PV_wiring/PV_Cable_wiring/_PV_Cable_Wiring.html> for an example of how we recommend transitioning from PV cable to building wire. William Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Blake Gleason *Sent:* Monday, April 26, 2021 5:41 PM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] MC4s are listed for THWN, right? Corey, Thank you! Agreed, the message from Staubli's Eng dept is much less confusing (with the exception of the statement about THHN tending to be solid vs stranded). All - What are you folks using to transition from PV Wire to THHN/THWN-2 inside a junction box? We used to use split bolts, which make an awesome electrical connection, but are time-consuming and not easily serviceable. Wire nuts (the right ones) are Listed, but never felt reliable for that purpose. Same for WAGO levers. I hear about people using Buchanan splice caps, but I wonder about trading one set of crimping problems for another. And of course, the only problem with using THHN in an MC4 is that the compression gland may not be as watertight as it is with PVWire, and the Buchanans certainly are not watertight. Terminal blocks generally aren't listed, definitely aren't watertight, and raise inspectors' eyebrows. Why is this so hard for me?? Best, Blake Thanks On Mon, Apr 26, 2021 at 5:19 PM Corey Shalanski <coreso...@gmail.com> wrote: Blake, In addition to Bryan's notes, here is some unconfusing information directly from Stäubli's engineering dept: The answer is categorically no: *you cannot use THHN wires with MC4 connectors.* There are several reasons for this: 1. *Certification*: our MC4 connectors are certified to UL6703, which only covers UL4703 PV wire or USE2 cable. Any other wire type is not covered by our certification 2. *Internal validation*: we have no internal testing or validation of how MC4 or Evo2 connectors perform with THHN cables. We therefore cannot warranty / accept the use of THHN cables with our PV connectors. The allowable cables and applications for our PV connectors is clearly stated in the assembly instructions. 3. *Construction*: THHN cables use very rigid PVC insulators, which behave very differently than XPLE or TPE insulators that are the most widely used on PV wires. PVC has a very low elastic range and easily deforms permanently under load/thermal cycling. It is not a well-suited cable for higher temperature or high temperature fluctuating applications where compression-type cable seals (i.e. cable glands) are used. Also, THHN cables tend to be single-conductor solid core cables, which are absolutely not allowed with crimp terminations like the MC4 (or any other PV connector on the market for that matter). They also are not allowed by UL6703. These comments were forwarded to me by Jeff Wang, who works for Stäubli North America. -- Corey Shalanski Jah Light Solar Portland, Jamaica On Mon, Apr 26, 2021 at 9:23 AM <bl...@sunlightandpower.com> wrote: Bryan, Thank you for the link. I am confused by the "PVC" section you referenced. Here's the complete text: For safety reasons Stäubli prohibits the use of PVC cables. Cables made from PVC can be connected to MC4-Evo 2 since the insulation material of the connector (Polyamide) is suitable to be connected to PVC. PVC cables usually have an upper limiting temperature of 70 °C, in fixed installations sometimes 80 °C. THHN/THWN-2 is made with PVC insulation, so I assume that it falls under the category of a "PVC cable." So, the first sentence seems to say that it's not allowed by Staubli. But then the second sentence seems to say that is IS allowed. And then the third sentence doesn't seem to be contemplating the most common PVC wire type of all (in the US), which is THHN/THWN-2, which has a 90 degree rating?! Can you help un-confuse me? Thank you! Blake _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org -- *Blake Gleason, PE | Employee Owner*Director of Innovation and Technical Excellence O: 510-845-2997 x128 C: 510-867-5878 1035 Folger Ave. Berkeley, CA 94710 www.sunlightandpower.com License #326203 <https://bcorporation.net/> <https://www.amicussolar.com/> <https://calssa.org/>
_______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
