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Wire Types


Louw
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Hi

 

I have just moved to a new house, with lots of North Facing Roof Space for more panels

 

Previously I have used 4mm "Solar Cable" from ACDC to wire up my panels to the MPPT and 25mm Welding Cable between the MPPT and Batteries.

 

Do you actually need to use Solar Cable (I am aware of the UV protection) between the panels and MPPT? Or can you use Single Core/Normal House wire?  Plan is to use the Solar Cable outside but convert to normal cable as soon as it is inside the roof. I have also seen discussion on using Speaker Cable? Any comments on this?

 

4mm Solar Cable (Single is around R1,360/100m at ACDC) vs 4mm Speaker Cable (Double at around R1,200/100m at Brights) - 55% saving!!!

 

Any inputs would be appreciated.  Trying to save some cost on wiring so that I can afford more panels!

 

Regards,

 

Louw

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Hi Louw,

 

Just an idea. I used PVC electrical pipes to protect the wires outside from the sun. It is cheap.

 

I would not use speaker wires, nor house wires. Wires are designed for a purpose.

 

Check the minimum spec required by the controller, for the wires from the panel to the controller.

 

Always use calculators like these, to confirm the wire requirements: http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

I know, these calculators never tell you want you want to hear.  :D

But losses over distance is a huge factor.

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What I remember of solar wire (the last time I used it) is that it has lots of small-diameter strands, whereas normal "house" wire has about 7 thick strands. This is for two reasons apparently: more strands means better mechanical strength, but more importantly, it means a greater total surface area, which in turn means more juice gets to go down there.

You should look up the voltage drop per meter of your cable. Also, I discovered through personal experience, that a 4mm cable carrying 35 amps gets warm to the touch (I temporarily rigged up an MPPT to a battery bank using solar wire, because I didn't have the required 25-35mm cable). While this is still within spec (spec sheet for the cable says up to 50 amps max in open air), I probably wouldn't do this.

So if the appropriate cable with multiple small-diameter strands gets hot at 30 amps... where do you think the house-wire is going to top out? :-)

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Basically the only difference between Solar Cable and stranded House Wire is the design of the insulation, Solar cable is UV/weather resistant and rated at 90deg C whereas house wire only rated at 70deg C.

I am using 4mm2 @ 16A max twin and earth (smaller sizes are solid copper) connected to the panels inside the roof and not exposed to weather.

 

At 35A I would go for 6mm2.

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Not 100% from the little I know guys. I am NOT an expert, but I tried all the shortcuts.  :P

 

Solar cable can be for indoor or outdoor, you ask for that when you buy it.

House wires that I know of, are either the lose wires in the wall in PVC pipes versus the 3 core soft insulation (no need for PVC) and then the 3 core wire that lie on top of ceilings, in the roofs heat.

 

Then, differences of single versus stranded: http://customcable.ca/stranded-vs-solid-wire/

 

And then you get down to the real facts:http://www.engineeringtoolbox.com/wire-gauges-d_419.html where the amount of cores dictate the amps. The more cores, the lower the amps.

To convert AWG to mm2: http://www.rapidtables.com/calc/wire/awg-to-mm.htm

 

And very important: Stranded wire, when you crimp them lugs on, has to be done right otherwise bubbles form and the lug heats up.

This is what happens when you crimp stranded wire, it becomes near solid, no air pockets: http://www.evdrives.com/category_s/4013.htm

And what if you don't: http://www.edn.com/design/components-and-packaging/4421838/Bad-crimp--bad-news

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