Wire Size

[eje]

Wow, I've received quite an education here. There is clearly a lot of knowledge on this forum. Thanks to all of you who helped.

As you all posted, I was reading & re-reading the manual, more carefully. I found all the references made

I am familiar with voltage drop, I just never considered it a factor in this application with the small devices and short runs - or the need to keep the drop below 3%. Interesting - While the manual does suggest 12 or 14 awg, I found an on-line calculator that shows the drop (12v dc, 7a for 10ft) for 12 awg would be 1.85% & 14 awg would be 2.95%.

[sailorboy1]

Another thing to consider to make the wire easier to deal with is to use 2-12 awg together on the same breaker. That reduces the voltage drop issue and the breaker is still sized for wire protection even if one were to somehow go bad.

I would have needed a 6 AWG wire and that was a pain so I used 2-10 awg on my system.

[Nicholson58]

One item to keep in mind is that wires too small is an issue by itself. Low voltage at some (induction) devices such as motors causes them to try to draw higher current. Best all around to err towards thicker wire.

[Nicholson58]

Originally Posted by sailorboy1

Another thing to consider to make the wire easier to deal with is to use 2-12 awg together on the same breaker. That reduces the voltage drop issue and the breaker is still sized for wire protection even if one were to somehow go bad.

I would have needed a 6 AWG wire and that was a pain so I used 2-10 awg on my system.

Did this on our solar farm. Wires on the panels are #8. I jumped them to #6 for the run to the 3-panel junction blocks. Short runs of #4 to the MPPT controller. Controller output to the batteries - 2 #4 wires. There was a rotary battery selector in the junk box with 8 circuits for #6. I paralleled these 2 X 2 to charge either of two house banks. On the best solar days we see 29 amps output at 28 volts from the MPPT.

[eje]

Originally Posted by sailorboy1

Another thing to consider to make the wire easier to deal with is to use 2-12 awg together on the same breaker. That reduces the voltage drop issue and the breaker is still sized for wire protection even if one were to somehow go bad.

I would have needed a 6 AWG wire and that was a pain so I used 2-10 awg on my system.

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The manual says a 'Dedicated drain wire' to ground is required and says it should be #10 or greater for less than 3' & #8 for more than 3'. Thought I'd use two 12's together.

[kmacdonald]

Originally Posted by RaymondR

Maybe, but 5 connections at a tenth of a volt per connection is half a volt.

It't might be a thousandths of a volt drop. The primary reason of minimizing connections is reliability. Corrosion starts at connectors and most wiring problem are at connectors.

[RaymondR]

Turning on a stationary DC motor can be the equivalent to dropping a short term, dead short onto the circuit. If you don't want to change the circuit to bigger wire you might try putting a couple of large capacity capacitors, say 2,000 mfd, across the power connection into the computer.

[smac999]

Originally Posted by eje

Wow, I've received quite an education here. There is clearly a lot of knowledge on this forum. Thanks to all of you who helped.

As you all posted, I was reading & re-reading the manual, more carefully. I found all the references made

I am familiar with voltage drop, I just never considered it a factor in this application with the small devices and short runs - or the need to keep the drop below 3%. Interesting - While the manual does suggest 12 or 14 awg, I found an on-line calculator that shows the drop (12v dc, 7a for 10ft) for 12 awg would be 1.85% & 14 awg would be 2.95%.

Keep in mind the wire is a loop. If it’s 10’ away. You normally need to put 20’ into the calculator. It should state round trip distance or something.