Solar PV install on farm

[cadspark]

A farm I have done some work for are having an array installed by a third party but I have been asked by the farmer to do some additional work not included in the PV install. At present there is a PME supply into a workshop from which a 25mm 2 core SWA has been buried underground and run to a barn where there will be a submain feeding the inverters for the array which is in a field. An earth strip has been put in the ground at the barn to TT the submain. I have had a discussion with the PV company today as they seem to think it acceptable to put a 100ma RCD upfront in the workshop before the SWA and only have an MCB on the submain protecting the PV inverters. My thoughts were the RCD needs to be on the submain and the SWA doesn't need RCD protections.
Your thoughts please.

 

[Gavin A]

1 - is there already a 300mA RCD at the main incomer?

2 - yes you're probably right if they've put an additional earth spike in at the sub board, although solar PV doesn't always need additional RCD protection on a farm situation other than the main 300mA RCD (unlike socket circuits), so I'm not sure what the 100mA RCD is supposed to be doing... if it's doing anything then it would probably need to be protecting the entire sub board in case the additional earthing interfered with the operation of the main 300mA RCD. Tbh though, I'd want an electrical engineer / experienced farm spark's opinion on what impact the extra earth spike at the sub board would have, as I'm not 100% sure.

What size system is it? if there's more than a 2-3 inverters 100mA may not be enough anyway.

 

[reelectrics]

more info required to give a better opinion but the rcd should be type a available via sibert solar with 100ma per inverter .

 

[Gavin A]

more info required to give a better opinion but the rcd should be type a available via sibert solar with 100ma per inverter .

if an RCD is actually required, which wouldn't be the case if there was already a main 300mA RCD... unless there were socket circuits also running off the sub board, but then it'd only be the sockets would need RCD protection... assuming it's all run in such a way as to mean an RCD wasn't needed.

At least I think I'm remembering the regs right, not got the BGB to hand.

 

[BruceB]

so I'm not sure what the 100mA RCD is supposed to be doing...

It is probably because he was talking to a sparks trained under the 16th edition who had a vague recollection that the practice for TT installs in domestic premises was to put a 100mA rcd upfront (sometimes time delayed if discrimination was needed with a 30mA rcd)

Anyway, in this case it is a farm and under current regs you need under 705.411.1 a 300mA rcd for all circuits other than sockets which have a lower requirement.

So if you have a 300mA rcd in the workshop that will cover you all the way to the inverter(s) even if you TT from say the barn. You could if there was a reason put one closer to the inverters as well. If you do then think about discrimination (time delay). But probably best not to have an additional one for the inverter(s) if not required.

 

[SibertSolar]

Gavin's right - the PV installation might not actually need an RCD....if the main board is already protected by a 300mA (max) all-pole RCD (section705) then maybe your only consideration would be the TT'd sub-main's Ze/Zs values to determine the requirement for an additional RCD or not, for ADS? If yes, then maybe the main RCD (if it exists) might need to be changed for an S-type? I'm not sure about that tbh.

Whether a TypeA or TypeB RCD would've needed (if an RCD is required) would depend on a couple of factors....what type of inverters are intended to be used?

 

[Pascaleto]

The main purpose of installing 300mA RCD is to prevent risk of fire, caused by electrical installation. Usually it is connected into the main board. 30mA RCD is preventing from electric shocks, from fault currents.
But the inverters may cause the triggering of RCD in their normal operation.

 

[jason121]

Define Agricultural farming. We work on a lot of farms and don't see any livestock. Also have never seen a 300ma RCD on incomer mains.

 

[JD6400]

Define Agricultural farming. We work on a lot of farms and don't see any livestock. Also have never seen a 300ma RCD on incomer mains.

Hi Jason , I know what you mean !
Personally I would class all properties where an agricultural practice is carried out , as needing a 300ma max RCD , as it is for fire risk from a higher content of combustible materials or vermin .
Having said that ! When dealing with some pack houses , they are so far removed from the average Agricultural install that I think you have got to treat them as such !?

As for TT systems , then that not only comes down to whether they have a holding number but also the potential of keeping livestock at all .

Well that's how I see it , would be interesting to hear what others say !?