Wire size for 240AC to load panel

[TekArt]

Hi, I'm a newbie here and I'm just starting a solar installation using 21 of the new Enphase micro inverters - each one will be fed by a BP175 panel. (The Enphase units convert DC to 240VAC in a small inverter right behind the panels and the AC circuits connect in series).

My question is this. I have to install a 240VAC load panel for the power coming from the 2 240V circuits coming from the roof. The inverters wire in AC strings with a max of 15Amp capacity. So I'm running 12/3 cable to the roof from the load panel in short runs of no more than 12 feet. But I'm not sure what wire size to use for the 25+ ft. run from the load panel to the main load center. In theory it will be carrying up to 30 Amps at 240VAC, so can I use the same 12/3 BX? or do I need to go up to 10 gauge wire?

You can read my blog about this installation at:

http://www.arttec.net/SolarPower/index.htm

Thanks
Guy

[Off Grid Solar]

Guy, please call Enphase with this question. They should be able to answer your questions. You see 175 watts at 240 volts should be a small wire! Enphase has your answer.

[indalecio.feng]

Hi, I'm a newbie here and I'm just starting a solar installation using 21 of the new Enphase micro inverters - each one will be fed by a BP175 panel. (The Enphase units convert DC to 240VAC in a small inverter right behind the panels and the AC circuits connect in series).

My question is this. I have to install a 240VAC load panel for the power coming from the 2 240V circuits coming from the roof. The inverters wire in AC strings with a max of 15Amp capacity. So I'm running 12/3 cable to the roof from the load panel in short runs of no more than 12 feet. But I'm not sure what wire size to use for the 25+ ft. run from the load panel to the main load center. In theory it will be carrying up to 30 Amps at 240VAC, so can I use the same 12/3 BX? or do I need to go up to 10 gauge wire?

You can read my blog about this installation at:

http://www.arttec.net/SolarPower/index.htm

Thanks
Guy

My answer is the output of all inverters should be in parallel.

And the bus wires should handle 30A~40A current. So the wire should be 10mm*mm at least.

[MarineLiner]

Enphase has visited to answer

Guy, please call Enphase with this question. They should be able to answer your questions. You see 175 watts at 240 volts should be a small wire! Enphase has your answer.

[Mike90250]

(The Enphase units convert DC to 240VAC in a small inverter right behind the panels and the AC circuits connect in series).

In theory it will be carrying up to 30 Amps at 240VAC, so can I use the same 12/3 BX?

or do I need to go up to 10 gauge wire?

I'll question your "AC circuits connect in series" as that would be very strange.

30 amps requires at least 10 gauge, and it may need to be inside conduit, where other
standards may apply. (90C wet rated?)

[TekArt]

series/parallel confusion

Thanks for the thoughts. I got my terms mixed up because the Enphase inverters have 4 pin connectors that connect in series for the 240 VAC, but of course the wiring is in parallel.

I will check with Enphase about the wire gauge. I was already planning to use flex conduit (BX) cable.

Guy

[Mike90250]

I will check with Enphase about the wire gauge. I was already planning to use flex conduit (BX) cable. Guy

Unless you live in the town of Enphase, you should check with your local building inspecting office. They are the ones who have to sign off on your project, along with your local electric company. You generally need to submit Plans First, Construct Second, and Inspection Third. Or else risk haveing your home insurance canceled, and the city cite you for un-approved additions, and electrical service cut off.
BX cable, in the USA, is generally only approved for short runs, and a ground (green) wire has to be pulled too. Check the spec for what type of insulation the conductors need while you are there.
< I think BX is the flexy, spiral, armored conduit ? >

[TekArt]

Good advice in general principle Mike. But I don't live in an urban area, I live in rural Maine where the local town does not require permitting for solar panels so far as I know. I do plan to talk to the fire chief - who is also the code enforcement officer as a courtesy. I'll walk him through the installation to educate him about the system and what firemen may need to know about solar panels in general.

[n3qik]

I would not use BX. It is not water tight and will rust quickly.

Look at this:

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100027582&N=10000003+90034+501108

[Jason]

hey Ken,

that link doesn't work

someone tried to post a home depot link in the past and it didn't work either.

[TekArt]

The BX would all be inside. I will run it from the under side of a Jbox that will be screwed down to the roof and bedded in silicone. Then the BX will run a few feet over and then down to the load center.

I have done a lot of residential wiring before, the only reason that I posted this question was my uncertainty about wire sizing. I think I'll use 10 gauge BX (designated as 10/3).

Thanks for all the helpful feedback folks!

[n3qik]

It is because of the store id.


Anyway, This is what I linked to:

AFC 1/2 In. x 100 Ft. Nonmetallic Liquid-Tight Flexible Conduit

[n3qik]

I will run it from the under side of a Jbox

Most new panels do not have the Jbox. They have gone to wires with MC-4 connectors.