Solar PV wages

[Gavin A]

if you work it out using bs7671 then 4mm is overkill using vd

mV/a/m x ib x L / 1000
2.5 twin is 18mV/a/m

so say 17amps for 4kw say 10m to the inverter

15 x 17a x 10 / 1000 =2.5v which is 1-1.5% depending on supply voltage

now as

where did the 15 come from at the start of that? surely that should be 18 x 16A x 10 / 1000 = 2.88V? which is 1.25% of the nominal voltage.

The problem is, if the supply voltage is coming in at say 251, then that 2.88V will push the inverter over the 253V nominal voltage limit, and with several inverters will cause nuisance tripping on the 10 minute average 253V setting, whereas if it had been 6mm2 the inverter wouldn't be tripping out.

The instant trip settings are up at the 263-264V range, so are reached more rarely, but can be an issue where multiple pv systems are installed on the same transformer

The a.c. cable connecting the inverter(s) to the consumer unit should be sized to minimise voltage
drop

The guidance is to minimise volt drop, I really don't see that 2.5mm2 meets that requirement other than where the inverter is installed at the grid connection point.

1% should be top end, not 1-1.5% is ok in a domestic setting.

 

[shanky887614]

where did the 15 come from at the start of that? surely that should be 18 x 16A x 10 / 1000 = 2.88V? which is 1.25% of the nominal voltage.

The problem is, if the supply voltage is coming in at say 251, then that 2.88V will push the inverter over the 253V nominal voltage limit, and with several inverters will cause nuisance tripping on the 10 minute average 253V setting, whereas if it had been 6mm2 the inverter wouldn't be tripping out.

The instant trip settings are up at the 263-264V range, so are reached more rarely, but can be an issue where multiple pv systems are installed on the same transformer


The guidance is to minimise volt drop, I really don't see that 2.5mm2 meets that requirement other than where the inverter is installed at the grid connection point.

1% should be top end, not 1-1.5% is ok in a domestic setting.

there are usually multiple settings for each region so you just need to selet the right region for that voltage range if its that close.

done it before and it wont cause nuisance tripping, how can it. a 17amp load on a 20amp+ breaker

 

[Gavin A]

oh, I see you've changed the distance to make your point valid.

Not sure how many cables you've strung from the CU to the inverter in a loft, but you'll almost always come up short at 7m IME.

besides, the requirement is to minimise the volt drop, not to use the smallest CSA cable you can possibly get away with based on the current carrying capacity.

 

[Gavin A]

there are usually multiple settings for each region so you just need to selet the right region for that voltage range if its that close.

done it before and it wont cause nuisance tripping, how can it. a 17amp load on a 20amp+ breaker

nuisance tripping of the inverter not the MCB.

so you mean you're not selecting the G83 settings on the inverter? or are you raising the reference voltage from 230 to 240V?

interesting, and likely against the G83 regulations unless you have advance permission from the DNO. But I'd have to ask, why not install the correct cable size in the first place?

 

[tom262]

this is all good and all that but its gone way off subject, how much do you guys charge??