keith.winston

Use of TC-ER/DG cable in Residential PV Systems

Discussion created by keith.winston on Feb 5, 2020
Latest reply on Feb 14, 2020 by keith.winston

Hello, I am a code official.

I have a PV installer who wishes to use TC-ER (Tray Cable - Exposure Rated) to run all the way to the panel or line-side tap, on the inverter-output side of the system (in this case it's a microinverter system, so virtually all wiring is the inverter output circuit).

My jurisdiction uses NEC 2011 but I'm willing to look at ANY NEC code that might clarify the direction this is going, since it is a fast-moving area of code. 

The code is a bit convoluted, so disagreements have occurred. I'm going to lay out a bunch of code, and then ask some questions at the end.

TC-ER doesn't appear in the 2011 NEC, or (I think) in 2014.

In 2017, 336.10(7) Uses Permitted, TC-ER-JP (Joist Pull) is called out as being allowed in 1 & 2 family housing, to be treated as NM (334) and UF (340) for interior and exterior locations respectively. The use for generators is explicitly mentioned.

336.12 specifies that it shall not be exposed to physical damage or installed outside a raceway except as provided for elsewhere.

It seems like all that indicates it can be used for 1 & 2 family PV systems, potentially. Wiring methods for PV systems would show up in 690.31: TC-ER doesn't show up in 2017, though 690.31(C) Multiconductor Cable does explicitly address that broad category, saying that it must be listed for the application and requiring max. 6' support spacing.

A newer development related to TC-ER, I believe, is type DG (Distributed Generation) cable. 

In the 2020 NEC, DG shows up in 690.31(C)2 as allowable in PV-related cable trays, and in the new (C)3 Multiconductor Jacketed Cable section, which itself includes a subsection:

(1) [DG is allowed] In raceways, where on or in buildings other than rooftops, and

(2)b. Protected or guarded, where subject to physical damage.

 

The question is: if one is running DG/TC-ER on a 1 & 2 family PV system, for the non-rooftop wiring, does it need to be in a raceway, and exactly when is the raceway required?

 

I am inclined to say a raceway is required, since 690.31(C)3(1) requires raceways, except where on rooftops.

An installer is arguing that the reference to the UF section 340 for outside installation of TC-ER is relevant, though I'll note that 2020 340.10(5) allows UF for solar PV systems in accordance with 690.31. To my mind, that brings us right back to the raceway: the installer would rely on 340.12(10) [not permitted] where subject to physical damage, that is, that as long as it's not subject to physical damage, which is a higher bar (and undefined) than merely "not on a rooftop".

One could try to draw a parallel between "subject to physical damage" and accessible, for example, and only require conduit in conditions where it is not "guarded by elevation". 

I would be interested in other's opinions on these points, if I've made them clearly enough.

It may be that a much shorter version of this question has appeared in the Members-only section, since I've requested a NFPA interpretation (which I can do as a Code Official), but I don't think I can see that section (I am not at this time a member).

Outcomes