# combining wire gauge formula

Posts: 62Solar Expert ✭✭
as my system grows, the need for thicker copper cables becomes increasingly apparent from the solar panels to charger to inverters. The battery cables are all 2/0 gauge..no problem. But the charge controller cables came with 4 gauge cables which get hot in full sun (100 amp input at 24volts). So i have doubled up the cabling and paralleled connected equal lengths of the 4 gauge cable (easier to do instead of re-wiring) Question is does 2 4gauge cables paralleled same length equal a 2 gauge cable ?...I assume yes and if so, what gauge would you end up with if you add a 2 gauge cable to a 4 gauge cable the same length ?? is there a formula for this ???

• Posts: 17,615Banned ✭✭
Re: combining wire gauge formula

Not exactly. It's a matter of two things: the actual area of the wire and the heat dissipating ability.

Look at this wire chart here: http://www.powerstream.com/Wire_Size.htm

If you take the resistance per 1000 feet you'll see 4AWG is about 0.25 Ohms. Double it gives approximately half that resistance or 0.125 Ohms which is roughly equivalent to 1 AWG. But the dual wires will actually be able to shed head better than a single one due to the larger outside surface (radiant) area.

Such wire paralleling is not allowed under NEC, btw, except for very large conductors. It's not good practice either. If you do it, make sure each wire length has fuse/breaker on it that will blow before its Ampacity is exceeded. You do not want to run both lengths through one fuse as one of the wires could 'go' leaving the other to carry the full current the fuse can handle.

Where is this 100 Amps @ 24 Volts coming from? That's 2400 Watts.
• Posts: 62Solar Expert ✭✭
Re: combining wire gauge formula

Great answer...forgot about the code thing...The current is all solar and I peak at 100 amps input for 3 hours in full sun from 11am until 2pm...I am using a combination of 15 solar mats (144 watt each) along with a mix of glass panels feeding into a large breaker box which then feeds into the charge controller/diverter through 2 gauge cables. The output of the charge controller came with standard 4 gauge wires feeding the large battery banks..this is where the wiring is hot at maximum sun power. Obviously heat= lost energy so I am trying to minimize current loss where possible. I am powering 4 3k inverters which essentially cover everything in my house except the large AC central air. I go off the grid everyday at 6am and back on at 7pm to begin the charging process. The current set-up has reduced my power bill by 50% over this time last year...a work in progress.....
• Posts: 17,615Banned ✭✭
Re: combining wire gauge formula

That Coleman controller is not well-designed if they claim it can handle 440 Amps but only allows 4 AWG on the output. There isn't a single wire made that can handle that much current. Sounds like hyperbole to me.

I know it's money but if I were you I'd be looking for a different controller. Maybe even two; one for each type of PV. Your 144 Watt units top 2kW and can probably output 70 Amps on their own. That could exceed the rating for 4 AWG (depending on particulars). Multiple controllers would be safer and more efficient than multiple wires on one controller.
• Posts: 62Solar Expert ✭✭
Re: combining wire gauge formula

....agreed the mats alone put out 70 amps in high sun. Thanks for the suggestions...