# Forum Home Renovation Solar Electrical Systems  Solar wire gauge question

## Window575

I'm wiring up my batteries and the MPPT charge controller. I've used 160amp wire for the 12V battery system in parallel, through to the 240V inverter. My question is does the wire gauge from the charge controller into the batteries have to be the same gauge (ie 160amp)?  
The solar people I bought the system from said I only need to use the 4mm2 wire that came with the panels (2 x 200W), but I'm not so sure. The 160amp wire is too large to fit into the charge controller terminals.
The inverter is 2800w, but don't intend to use it's full capacity. Might draw 1500W at the most. 
4mm2 or 160amp? 
Thanks.

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## Random Username

Might need a few more specs.... a cable capable of carrying 12 volts/160 amps DC will be somewhere in the region of 35-40mm diameter.  The ah refers to the charge holding capacity of the battery.  What's the maximum charging current that the (whatever) can deliver to charge the batteries? 
But a good guide is the controller terminals - if the cable is too big to fit, it's oversized for the rated output (assuming decent engineering and not chinese 'we have 10,000 of these on the shelf that were rejected by the firm whose design we are ripping off' engineering).

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## Window575

Sorry meant to type amps (a) not ah....duh. Will edit now.
The terminals on the charge controller will only take 10mm diameter cable. The cable I have for the batteries and inverter is more like 14mm. 
The controller is a 30A unit. 
Thanks mate.

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## Random Username

Minimum 6mm assuming your run is only short (10 meters or so).  If you have a longer run, you might want to take voltage drop into account and upgrade to 10mm.

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## UseByDate

> Might need a few more specs.... a cable capable of carrying 12 volts/160 amps DC will be somewhere in the region of 35-40mm diameter. 
> .

  Are you sure this is correct? 40 mm diameter cable to carry 160 amp seems excessive to me. :Confused:   :Confused:

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## commodorenut

One would assume he means 40mm2 cable, which has a much smaller diameter, but it can be very misleading to those who don't understand cable sizes!

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## Marc

I would install 50 mm diameter just to be on the safe side ...  :Smilie:  
A quick calculation tells me that a 50mm diameter is over 1900 mm2 and a 40mm2 is a tad over 7mm diameter. Talk about misleading ! 
surface of a circle is the square of the radius (diameter /2) times 3.14

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## UseByDate

Plus a “tad” more for the air between the wire strands in the cable.
 I assume you are using the metric “tad” in this context. I prefer to use the imperial “tad” when dealing with SWG (Standard Wire Gauge). :Smilie:

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## commodorenut

Not that I've ever seen it, but if it were a single strand... then Marc is spot-on  :Smilie:

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## Marc

Now now you two ... you are straining the gnat, are you telling me you have never seen a 1900mm2 single strand wire?  :Smilie:  
I remember working in a shut down where a guy got busted for smuggling a foot of (304.8 mm give or take a metric tad) a very thick single strand cable stored in the warehouse. It was easy 50mm in diameter and in a massive roll. This guy would go everyday with a hacksaw and cut a bit off and put it in his lunch box. Eventually he got busted.

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## oldtrack123

> I'm wiring up my batteries and the MPPT charge controller. I've used 160amp wire for the 12V battery system in parallel, through to the 240V inverter. My question is does the wire gauge from the charge controller into the batteries have to be the same gauge (ie 160amp)?  
> The solar people I bought the system from said I only need to use the 4mm2 wire that came with the panels (2 x 200W), but I'm not so sure. The 160amp wire is too large to fit into the charge controller terminals.
> The inverter is 2800w, but don't intend to use it's full capacity. Might draw 1500W at the most.

  Hi I
If you are referring to the battery charging lines from the MPPT controller ??, the size will depend on the solar panels total rating, the battery bank voltage & the actual distance the cables have to run[A to B]
The size you use for your inverter has nothing to do with the solar[Unless you are using a MPPT that monitors load }
And for 160A Short distance  1 B&S/AWG[42 sqmm cross sectional AREA[NOT DIA],which is around 7.5MM. actual copper dia] or  50mm metric cable has a continuous current rating of 165A

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