Residential AC wire run and voltage drop considerations

[bbartmasse r]

Hello there,

I am installing a SolarEdge 7600 on a new job. It has a rated output of 32 amps (which it's unlikely to ever see).

The wire run from inverter to panel ended up being about 90 feet, further than I typically have to go but the contractor wanted it in a specific location and I could not really argue.

I did the voltage drop calcs (#8 copper is what I used) and they seemed fine but it made me wonder if there were any special considerations to make for inverters that I am not aware of in regards to voltage drop?

thanks.

Brett

 

[Dennis Alwon]

You should be fine with #8-- of course the load is the only way to do a calculation. Even at 32 amps there should not be an issue. I don't know why the inverter would change the VD calculation on the load side

 

[ggunn]

Hello there,

I am installing a SolarEdge 7600 on a new job. It has a rated output of 32 amps (which it's unlikely to ever see).

The wire run from inverter to panel ended up being about 90 feet, further than I typically have to go but the contractor wanted it in a specific location and I could not really argue.

I did the voltage drop calcs (#8 copper is what I used) and they seemed fine but it made me wonder if there were any special considerations to make for inverters that I am not aware of in regards to voltage drop?

thanks.

Brett

One thing in general to consider is that when the inverter is sourcing current, voltage drop is really voltage rise as far as the inverter is concerned. The voltage at the service is unlikely to be changed much if any at all by the current injection by the inverter, so if your voltage drop is 2%, or 4.8V on a 240V service, the voltage at the inverter will be higher by that amount when it is running at maximum output. If you scrimp on wire size for a long run, you could drive the voltage at the inverter high enough to cause it to shut down.

 

[Carultch]

Hello there,

I am installing a SolarEdge 7600 on a new job. It has a rated output of 32 amps (which it's unlikely to ever see).

The wire run from inverter to panel ended up being about 90 feet, further than I typically have to go but the contractor wanted it in a specific location and I could not really argue.

I did the voltage drop calcs (#8 copper is what I used) and they seemed fine but it made me wonder if there were any special considerations to make for inverters that I am not aware of in regards to voltage drop?

thanks.

Brett

Blanket specs often call for designing voltage drop to not more than 2% on either the AC or DC side, and not more than 3% grand total for the PV system. There really is no formal rule on how much you are required to limit resistive losses in a PV system, other than how much inefficiency you want to allocate to resistive losses in your performance modeling, and how much you want to limit the risk of nuisance tripping the inverter's internal relay.

 

[jaggedben]

Most 240V services around here frequently read at 250V. Since inverters will trip off at 264V, you really have 5% before it's a major problem. Not that you want to cut it close. Keeping it to 2% results in more payback, of course, although on a long run it may or may not ever payback the cost of bigger wire.

 

[Carultch]

Most 240V services around here frequently read at 250V. Since inverters will trip off at 264V, you really have 5% before it's a major problem. Not that you want to cut it close. Keeping it to 2% results in more payback, of course, although on a long run it may or may not ever payback the cost of bigger wire.

While the official relay settings are factory set to 110% of nominal per the IEEE standards, some inverters might be built with a secret safety factor below this, in order to reliably pass the testing. So even though you could get by in theory with a 5% voltage drop on the AC side, on a 250V actual of a 240V service, you might have unexpected nuisance tripping, even below 264 Volts.