Author Topic: Inverter Wire Size  (Read 9476 times)

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kittysmitty

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Inverter Wire Size
« on: February 11, 2009, 08:44:20 PM »
What size wire and fuse should I use for a 1500 watt inverter, 12 volt, distance from battery 5 feet. I have searched for info, but get very different answers. Thanks
« Last Edit: February 11, 2009, 08:44:20 PM by (unknown) »

richhagen

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Re: Inverter Wire Size
« Reply #1 on: February 11, 2009, 02:31:47 PM »
If we assume a maximum power of 1500 Watts out of the inverter, at about 80% efficiency and a low point operating voltage of 10V, then (1500/.8)/10 would give about 187.5 Amps.  I would probably size it for about 200 Amps of current which would yeild a cable size of about 0 guage minimum (which is about 52.6 square milimeters), with a cable protection device of a fuse or circuit breaker at 200 amps as near to the battery end of the cable as practical.  The manuals for most inverters usually specify minimum cable sizes and recommended circuit protection devices.  In general it will not hurt you to use a larger cable size if the connections on the inverter and the batteries can handle them.  I generally try to mount a fuse at the battery and then a lower rated circuit breaker at the other end for convenience.  In normal operation, the breaker will trip first at the lower amp rating, but the fuse is there just in case of a short in the cables from the batteries.  Murphies law still applies you know.  Rich  
« Last Edit: February 11, 2009, 02:31:47 PM by richhagen »
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SteveCH

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Re: Inverter Wire Size
« Reply #2 on: February 11, 2009, 05:00:12 PM »
When I was putting the Inverter into my system [and mine's 12 v., too, though a 2500 W. inverter], a buddy of mine who is a physicist was visiting a few days and fascinated with the pv, etc. He said, in relation to a question I had that mirrors yours, "Between the batteries and the inverter, don't scrimp on wire gauge. After you calculate the gauge you need, make that your bottom line and then go as large as you can stand." Of course, as the previous poster said, you gotta be able to connect it to the terminals, which will ultimately limit the connectors you choose and use....
« Last Edit: February 11, 2009, 05:00:12 PM by SteveCH »

SparWeb

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Re: Inverter Wire Size
« Reply #3 on: February 12, 2009, 10:57:40 AM »
Recommended reading:

If you were to do a google search for John Wiles, NEC code for photovoltaic systems, you would find a very helpful manual that shows you a plethora of "how-to" stuff like this.  It's a fairly big PDF, but worthwhile.  On the very last page (or nearly) is an appendix with inverter input demands measured for a common model of inverter.  The results are surprising!
« Last Edit: February 12, 2009, 10:57:40 AM by SparWeb »
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Airstream

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Re: Inverter Wire Size
« Reply #4 on: February 12, 2009, 11:11:24 AM »
For us people with dial-up think you could get a true link to the whole document?


I am especially interested in the inverter draw data you mentioned...


http://photovoltaics.sandia.gov/docs/John_Wiles_Code_Corner.htm

« Last Edit: February 12, 2009, 11:11:24 AM by Airstream »

SparWeb

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Re: Inverter Wire Size
« Reply #5 on: February 12, 2009, 11:56:59 AM »
I got lead to John Wiles' Code Corner, too, but that's not where the big document is.


It's on Sandia Labs' server (643 Kb, 117 pages):


http://www.re.sandia.gov/en/ti/tu/Copy%20of%20NEC2000.pdf


Oh man, I just realized that the OLD one... but it does have the inverter data in it.

Still looking for the 2005 version.

« Last Edit: February 12, 2009, 11:56:59 AM by SparWeb »
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

SparWeb

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Re: Inverter Wire Size
« Reply #6 on: February 12, 2009, 12:01:34 PM »
Here it is  (4.0 Mb, 143 pages):


http://store.altenergystore.com/media/pdfs/photovoltaic_NEC_code_practices2005.pdf


The chart is on page 119 of this one, and there are a lot of other appendices added on to the end, now.

« Last Edit: February 12, 2009, 12:01:34 PM by SparWeb »
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

richhagen

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Re: Inverter Wire Size
« Reply #7 on: February 13, 2009, 04:32:22 PM »
Steven, that is a wonderful link.  I am looking to improve my current solar installation, and plan to review this document prior to undertaking that task.  Rich
« Last Edit: February 13, 2009, 04:32:22 PM by richhagen »
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