Wire sizing for the in going wires from pv to the mppt.

[Fraser]

Hi everyone. I have another wire sizing question. I have an mppt victron 250/100, the in going wire size I thought would be 16mm2/ 6 AWG but is that the case given the voltage 183 volts going in along with just over 40 amps. I have heard thinner wires for more voltage but better insulation. Will 16mm2 do the job?

Many thanks in advance

Fraser

 

[LB3]

16mm is nearly 5AWG so the amperage is safe. Depending on the length of your run you may need to go larger.

 

[Forbisher]

Hi everyone. I have another wire sizing question. I have an mppt victron 250/100, the in going wire size I thought would be 16mm2/ 6 AWG but is that the case given the voltage 183 volts going in along with just over 40 amps. I have heard thinner wires for more voltage but better insulation. Will 16mm2 do the job?

Many thanks in advance

Fraser

Nobody can answer your question without all the info.

First what is your panel layout?
How many watts and specs.
Voc
Vmp
Imp
Isc
Connected?
Series
Series and parallel
Distance from panels to SCC?

 

[snoobler]

The maximum current that unit can handle on PV input is 70A. 6awg is more than sufficient. 10awg would be fine for anything less than a 50' run:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

Wire size depends on 1) current and 2) voltage drop.

You select your wire based on the current rating. Then you assess if the voltage drop is excessive based one Vmp, Isc, and distance. If too much voltage drop, fatter wire.

In your case, you would look at the drop for each string using 10-12awg PV cable and distance to the combiner box. Then you would look at your entire array's Vmp/Isc and distance between the combiner box and the MPPT.

Assuming 4S4P and 10awg throughout.

Assuming each string is 20' from the combiner box, 183V/10A over 20' is a 0.22% loss.
Assuming combiner box is 15' from the MPPT, 183V/40A over 15' is a 0.65% loss.

In total, you'd have a .65 + .22*4 = 1.53% loss. Most folks accept 2-3% loss. Well. I do, anyway.

For reference, your 5-6awg wire would have the same loss over a 100 ft run.

Note that the particular calculator I linked is ONE-WAY distance.

 

[Fraser]

16mm is nearly 5AWG so the amperage is safe. Depending on the length of your run you may need to go larger.

Thanks for the reply. It’s only about 3 ft. Is it better to just go larger to be on the safe side?
cheers

Fraser

 

[snoobler]

Thanks for the reply. It’s only about 3 ft. Is it better to just go larger to be on the safe side?
cheers

Fraser

It's mostly about cost and if the wire fits in the terminals. The only thing bigger wire hurts is your wallet.

 

[Forbisher]

Thanks for the reply. It’s only about 3 ft. Is it better to just go larger to be on the safe side?
cheers

Fraser

If you have more than a few solar panels how could the wire length only be 3 feet?
Where are your panels installed?

 

[Fraser]

It's mostly about cost and if the wire fits in the terminals. The only thing bigger wire hurts is your wallet.

Yeah. It’s all hurting my wallet at the moment. What will hurt more is if I have a fire. Yes fitting the terminals. I have to fit 35mm2 in the out going because it’s 100 amps. I think the mppt manual says that’s the largest it can take. I think...... I have read so many Manuals my brain hurts.

Thanks for your help

Fraser

 

[Fraser]

If you have more than a few solar panels how could the wire length only be 3 feet?
Where are your panels installed?

Panels are on the roof. But they are going to come down in strings each one fused then going into 2 two string dc isolators and then being parallel wired together. It’s the bit when they all join together around the isolation switches and then a short distance to the mppt. That’s the way I have been told to do it anyways.

 

[Fraser]

The maximum current that unit can handle on PV input is 70A. 6awg is more than sufficient. 10awg would be fine for anything less than a 50' run:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

Wire size depends on 1) current and 2) voltage drop.

You select your wire based on the current rating. Then you assess if the voltage drop is excessive based one Vmp, Isc, and distance. If too much voltage drop, fatter wire.

In your case, you would look at the drop for each string using 10-12awg PV cable and distance to the combiner box. Then you would look at your entire array's Vmp/Isc and distance between the combiner box and the MPPT.

Assuming 4S4P and 10awg throughout.

Assuming each string is 20' from the combiner box, 183V/10A over 20' is a 0.22% loss.
Assuming combiner box is 15' from the MPPT, 183V/40A over 15' is a 0.65% loss.

In total, you'd have a .65 + .22*4 = 1.53% loss. Most folks accept 2-3% loss. Well. I do, anyway.

For reference, your 5-6awg wire would have the same loss over a 100 ft run.

Note that the particular calculator I linked is ONE-WAY distance.

I was recommended 12 Awg for the strings. The panels are on the roof of a barn and the barn has a loft where the stuff is going to be. Not much distance from panel and mppt. Except the panels at the far end of the barn roof will have to travel 30ft to meet the ones towards the other end of the barn where the mppt and all the other shiny victron stuff is. ?

 

[snoobler]

Given the low voltage drop of the 10awg/20', 12awg should be fine.

 

[Fraser]

Given the low voltage drop of the 10awg/20', 12awg should be fine

Thank you. Your knowledge and reassurance are highly appreciated.

Fraser