Ac cable size ???

[grandfortune]

becuase a RCD has a disconnection time of 0.4 sec where the inverter has a disconnection time of 5 sec, so if the rcd trips the inverter will pump power down any circuits on that RCD side and you dont want that.

 

[BruceB]

You are making up your own rules there which are not in 7671 or G83/1. Mostly disconnection times for inverters are below 5s.
Regards
Bruce

 

[malcolmsanford]

Grandfortune a 30mA RCD which is the common one for domestic purposes is not 0.4 but 0.04 and as BruceB kindly posted most inverters disconnect well below your 5s disconnect time.

So why are the powers to be advising that a PV system needs to be on separate protection? I was told once on here that it is because of regulation 314.2, and I would dispute that also

 

[Graeme Harrold]

With regards to Solar and Reg 314.2 kind of needs to be looked at in reverse. You dont want the PV system taking out the RCD protecting the remainder (or half of) the property circuits. I always provide a dedicated/protected circuit either by a single way CU on a henley, or a dedicated RCBO. More good practice than by the regs (litterialy)

 

[malcolmsanford]

Thanks Graeme but why are inverters taking out RCDs. I install many small stand alone UPS systems here all on RCD protection and very very few have taken out RCDs, even when they have had mains power failure.

This is what I'm asking, is it because of the start up every morning? Are there high protective conductor currents in use on the inverters that are used in PV installations?

Becasue if it is a case of protective conductor currents then should not reg 531.2.4 be cited?

 

[Worcester]

@Malcolm, If I remember right the UPS's don't back feed do they? The current still flows the same way?