Installing Photovoltaic system

[Jie]

im installing a 3.96kW System on a farm. The main board in the house is roughly 100 metres away from where the solar panels are going to be placed.

they will be outside in a field where decking is being put down. i have measured up a 10mm swa cable buried will be suitable as ther is only a 2.8% voltage drop due to length of cable.

can i take the cable to a small 30mA RCD protected Garage Unit (small C.U) 16A breaker as an isolator, then to the existing house C.U to a 16A breaker? and would this have to be on an RCD also?

 

[Markc]

Can't see the need for a garage CU outside. What not just use a rotary isolator? RCD and 16amp protection can be in the house with a second rotary isolator as well. Isolators must be able to be locked off and a MCB does not meet that.

 

[poheZ]

why cant an mcb be locked in the off position?

 

[Jie]

"can i take the cable to a small 30mA RCD protected Garage Unit (small C.U) 16A breaker as an isolator, then to the existing house C.U to a 16A breaker? and would this have to be on an RCD also? "

this would be on the inside of the house. there would be another ac isolator beside the waterproof inverter outside.

 

[malcolmsanford]

Is there any particular reason you want all these protection devices? Where are you siting the invertor?

 

[JulianC]

If I was doing this, I'd have a lockable rotary isolator adjacent to the inverter outside, then run the cable back to the house to another lockable rotary isolator (the "main PV AC isolator"), followed by the gen meter and either a 16A RCBO in the CU, or a separate RCD then into a 16A MCB in the CU. I'm assuming you are installing the RCD due to it being a special location (agricultural premises) - section 705 of the BRB, where an RCD up to 300mA is required.

Also bear in mind that good design practice is to limit the AC volt drop to within 1% on PV systems, not the usual 3% we are used to (sommat to do with preventing the inverter throwing a wobbly).

why cant an mcb be locked in the off position?

It can, but not without use of a special tool. An isolator than can be locked in the off position (and only in the off position) by any common or garden padlock is required.