I design a lot of grid tied projects, but I still do a rooftop about once
or twice a year. All of them going back 7 years or so always used
covered/vented cable tray. This includes homeruns, DC feeders, and all AC
wiring. There still is some metallic conduit used (usually EMT) - a small
jumper for a single wire, or the 3'-5' jump from the cable tray to the
inverter or panelboard, or a single circuit output. Cable tray is a lot
more cost effective and it has thermal expansion inherently built in so
there's less concern about separation. You can also fill up a smaller area
than conduit so it's a bit easier to walk around, although we have to
install some stairs to go over some of the more crowded spots.
It gets a little complicated and labeling is incredibly important as you
don't want to mix DC and AC wires in the same tray, nor can you mix
communication cables in it either.
I haven't done once under the Jan 1 2019 rapid shutdown clause yet nor do I
see one on the horizon anytime soon but I see no reason why cable tray
still won't be used.
> Date: Sat, 25 Jul 2020 01:00:03 -0500
> From: Corey Shalanski <coreso...@gmail.com>
> To: re-wrenches@lists.re-wrenches.org
> Subject: [RE-wrenches] Rooftop Conduit
> Message-ID:
> <CAJ6f=
> nhj27yoxvtu0o7gjecpbpffcommq+mrxjlzeqvap2t...@mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Wrenches,
>
> I noticed a couple good threads ("Cable tray" / "PV Wiring methods") about
> this topic back in 2013, but I haven't seen much discussion since then.
> Given some of the advances in PV equipment since then (improved
> ground-fault protection, arc-fault circuit protection, rapid shutdown), I
> am curious about current attitudes toward using metallic conduit/cable tray
> on rooftops. I am primarily interested in hearing about flat commercial
> rooftops but imagine some of the same conventions may apply for residential
> rooftops.
>
> What are you using for long (or short) dc circuit runs on rooftops? Is
> cable tray still considered safer? Are there situations where conduit may
> be merited? If so, is RMC favored over EMT?
>
> Do best practices change when considering ac circuits (rather than dc)?
>
> Back in 2013 Bill Brooks said that PV installers are the "crazy people"
> installing conduit on rooftops, and he prophesied that using cable tray on
> roofs would "become common practice soon." Where do we stand now?
>
> --
> Corey Shalanski
> Jah Light Solar
> Portland, Jamaica
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>
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