Ac vd

[Jimbo2]

Hi,

1% volt drop from the inverter to the consumer unit, is this 1% rule really required, or can i go above ?

Power one inverter ..

Thanks James

 

[BruceB]

The Guide says it all really:

"The a.c. cable connecting the inverter(s) to the consumer unit should be sized to minimise voltage drop. A 1% drop or less is recommended. However in larger installations this may not be practicable or economic due to the very large size of cable resulting. In this case the designer should minimise voltage drop as far as possible and must remain within voltage drop limits as prescribed by BS 7671.
Note: The recommendation for a 1% voltage drop is due to two reasons: firstly when generating, the voltage at the inverter terminals is higher than the voltage at the supplier’s cutout – during periods of high power output this voltage drop must be kept to a minimum in order to prevent the inverter nuisance tripping on over voltage ; secondly the requirement ensures losses from the PV
system are minimised."

If you are the designer you have to make your mind up and then justify afterwards if required.

 

[Gavin A]

no excuse for not achieving 1% on a domestic install mind - at least not a standard one, maybe if you're doing ground mount a couple of hundred meters away down the garden or something.

 

[SolarCity]

I tend to design with 1% in mind. It does make it expensive on long cable runs but I would seriously hate to have to dig up and upgrade a buried cable if problems were experienced later.

 

[Jimbo2]

yep, thanks again for your support i will work to the 1% rule

 

[Gavin A]

yep, thanks again for your support i will work to the 1% rule

it's also important that you actually understand why this is important for solar PV rather than blindly following a rule.

In some situations even the 1% rule isn't really strict enough, and problems can result even if it's followed.

 

[SolarCity]

That's a fair point. Testing the incoming voltage is a pretty important part of a survey. But you do have to consider the possibility that grid voltages may rise.

 

[Jimbo2]

Thanks again for the advice. i will check the incoming voltage and apply the logic. I have my MCS inspection next week so i hope all is well, but im still concerned about earthing the array frame work, DTI tree it will be, thanks again to you both James

 

[Gavin A]

put the DTI guide away, it has been superseded by the MCS guide.

 

[Jimbo2]

will do thanks