Earth to an isolator?

[Cupatea]

I am about to install a 3-phave PV system connecting the DB MCB to the isolator (IMO) in 4-core SWA and from the isolator to the inverter in 4-core Kopex flex plastic conduit. I am planning on running the separate earth from the DB direct to the PV PE point. The SWA armour will be earthed at the DB end only.

My question is: should I run the earth into the isolator & back out again, using the earth tags inside the IMO or just by-pass it with a direct earth cable. I would prefer the latter as there won't be too much room in the isolator for 4-core 10mm and a 10mm singles.

Any ideas/ thoughts gratefully received!

 

[davesparks]

The regulations require the cpc to be taken to every point in the circuit.
Why do you need a seperate earth? Is it a cpc or a bond?

Using a better quality isolator may give you more room inside. I prefer Craig and Derricot personally

 

[Simonslimline]

Used a Craig and Derricott Isolator a couple of weeks ago, found it really good design and quality. Actually some room to dress the cables inside it.

 

[Cupatea]

It's the cpc - have to use the IMO as thats what is supplied, unfortunately, not my choice.

 

[davesparks]

Then it needs to terminate at each point in the circuit.
There's nothing to say that it can't go to the load first then back to the isolator. I've done this before with some jobs where the cpc is only going to the isolator to satisfy this reg and not performing any function

 

[Cupatea]

Thanks, Davesparks! That's what I'll do - run the cpc back from the inverter so only one single in the isolator. Not so much of a squeeze now!

Another small query- does the cpc have to be the same size as the conductors? Circuit is 25kW, 3-phase. Using online cable calculators, using xlpe swa I can get away with 6mm, 4-core (4m run) - but using 10mm as its 'feels' better.

 

[davesparks]

Thanks, Davesparks! That's what I'll do - run the cpc back from the inverter so only one single in the isolator. Not so much of a squeeze now!

Another small query- does the cpc have to be the same size as the conductors? Circuit is 25kW, 3-phase. Using online cable calculators, using xlpe swa I can get away with 6mm, 4-core (4m run) - but using 10mm as its 'feels' better.

Cpc size should be calculated using the adiabatic equation. I don't see how you can know you need a seperate cpc if you haven't done the calculations yet?


Don't use an online calculator! Get your regs book out and calculate it properly. Bearing in mind the stricter VD requirement of PV.

 

[Leesparkykent]

543.1.3 and 543.1.4