Wire Size

14 Posts
Oct 31, 2008 08:47 pm
Wire Size

Can someone calculate the wire size I would need to connect a set of 6--175 watt panels at 24v from the combiner box to the DC disconnect/charge controller/inverter ( all to be located right next to each other)  Distance is 60'  I have a quite a bit of #2 copper and aluminum wire, and can parallel it if necessary.

Thanks in advance !

« Last Edit: Oct 31, 2008 08:49 pm by Andy Davenport »
220 Posts
Oct 31, 2008 10:05 pm
Re: Wire Size

 hi andy,

 our host has an easy to use calculator that does a nice job at wire run sizing.


 when we plug in our info it looks like an acceptable 3.5% voltage drop using that awg#2 cu wire you have. 2% is what to shoot for but up 5% would be a go. (depending on the pv module)

 the same #2 wire from controller to battery bank is good.

 as far as the cable from battery to inverter goes, that would depend on the inverter size but we really want to go for the overkill with this connection. nice big lugs,oversize wire size and short run. ie.#00 cable minimun and five feet max. (my opinion only)

 andy. i would rethink my charge controller options. even with the biggest 60amp pwm controllers we are right on the max or even over with the derate. think about going with one of the open format mppt units. you will be able to come down at much higher voltages at reduced current with a very reasonable wire size and have better pv production with the muiti(sometimes called maximum) power point tracking.

 also, maybe it's just me but i don't like any aluminum wire in any part of a dc power system. it's great for ac subpanel service runs tho. (opinion only)

best regards,
578 Posts
Nov 1, 2008 07:09 am
Re: Wire Size

i use the wire size chart in this book all the time.


in parallel, you would have roughly 30a at 24vdc nominal.  2awg would make it 52 feet for 2% v-drop.

by contrast, if you could wire them at 48v in series parallel with an mppt as david mentions, you would have 15a at 48vdc nominal coming in, which could mean you could use #6 wire for 2% drop for 81 feet.  you can use the #2 from the controller to the battery bank.

also if your system expands by double, you would be okay with #4 or #2 if you were to wire at 48v and have 6 strings of 2 of the same type of modules and an mppt controller such as an mx60.

good luck,

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10 Posts
Nov 27, 2008 01:57 pm
Re: Wire Size

I came across your post and thought I'd share a link I've found useful for this sort of thing. The page has a data table with a handy calculator below it.

You mentioned elsewhere that you have a long run of #8 wire: are you running 120VAC, and do you convert it to DC at the end?


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