Section 705 for agricultural installations

[SibertSolar]

Hi all,

Can anyone clarify how/when an installation falls under Section705 for agricultural? Does livestock have to be present in the building that the PV installation is being fitted to? How about RCD protection if the supply isn't TT? Is it mandatory to fit an RCD to the PV feed/distribution circuit before connecting to the main incomer? Even if an RCD isn't required for ADS under BS7671?

Just curious as there's a lot of agricultural work going on out there at the moment, some with and some without livestock present, and I was curious as to what people are doing from an RCD protection point of view.

Thanks in advance

 

[JD6400]

Not to sure for your first question as even if livestock is not present at the moment it could there tomorrow , so i would say err on he side of caution and treat as a stocked farm !?
I suppose if the premises has a holding number that would be one way of looking at it ?

As for not being a TT supply , unless it has all the required precautions in place ( as rare as hens teeth ) then it has to be TT.

 

[reelectrics]

special location so 300ma 4 pole rcd required at service head then mcb at tpn .Design considerations apply if using g59 relay ie over 50kw installed as you will require two tpn fitted with rcds to allow discrimation and prevent nuisence tripping at service head .Doepka can supply 400ma rcd via sibert which can be used on four inverter systems but does not technically comply with sect 705 as 300ma rcd is cited tt or tn-s.This also applies to ground mount systems .

 

[SibertSolar]

Hmm, seems my post disappeared, I'll try again....

Thanks eelectrics, that's exactly as I thought - 300mA (max) 4P RCD protecting multiple MCB-protected feeds in a TPB board. Multiple boards needed if combined trip limits/current limitations are being exceeded, but does discrimination apply in an SSEG scenario? Avoiding nuisance tripping is a tricky one as installers will only have the inverter manufacturer's recommendations on minimum trip limits to work from, even though reality may allow some flexibility (4pcs SMA TL inverters on a 300mA trip limit RCD, for example, may well not cause an issue in reality). So, any more than 3 inverters and a 2nd TPN board would be needed I guess.

Ground-mounted systems is also something I am keen to understand people's habits in terms of circuit/surge/lightning protection. Does fencing (suitably bonded/earthed etc) make a difference to decisions made regarding protection?

 

[reelectrics]

There is very little guidence on ground mount systems in the new dti guide .Have any systems been damaged due to the floods and what are the insurance /warrenty and installer implications.

 

[MarkieSparkie]

BS7671:2008+A1:2011 Section 705 applies to the fixed electrical installation of any building, location or area, indoors and/or outdoors, in an agricultural or horticultural premises. The only exceptions are any rooms, locations or areas intended solely for household applications where the general regulation requirements apply, or electric fence installations where BS EN 60335-2-76 applies.

 

[Gavin A]

Hi all,

Can anyone clarify how/when an installation falls under Section705 for agricultural? Does livestock have to be present in the building that the PV installation is being fitted to? How about RCD protection if the supply isn't TT? Is it mandatory to fit an RCD to the PV feed/distribution circuit before connecting to the main incomer? Even if an RCD isn't required for ADS under BS7671?

Just curious as there's a lot of agricultural work going on out there at the moment, some with and some without livestock present, and I was curious as to what people are doing from an RCD protection point of view.

Thanks in advance

We're doing a farm installation now, so I've just checked and we are meeting everything in section 705 as it's mostly common sense really.

assuming some jobsworth doesn't want us to bond together all the structural steels on the barns that each individually have a better Ze reading than any earth rod I've ever seen, certainly a damn site better than the rods at the main supply point which we're doubling up.

 

[SibertSolar]

Thanks Gavin, TT supply? Are you fitting a 4P RCD (Type?) rated no more than 300mA? Just trying to get a feel for what people are doing.....

 

[Gavin A]

Thanks Gavin, TT supply? Are you fitting a 4P RCD (Type?) rated no more than 300mA? Just trying to get a feel for what people are doing.....

As far as I know, so long as there is already a 300mA RCD at the main supply point covering the entire installation then no additional RCD would be needed, as the circuit is automatically protected by that RCD.

The RCD already exists as it should on all agricultural premises, and we've tested it and it's fine, so we're covered.

socket circuits would need 100mA RCD's fitting, but I'm not in the habit of fitting sockets to my PV circuit...

I'd not class myself as an expert on farm electrical installations though, but that's my reading of the regulations.

 

[SibertSolar]

Thanks again Gavin. I didn't imagine for a second that you would ever put a socket on a PV circuit! (Unless it's for a data logger/monitoring device....) as for not being an expert, I'd say that I and a good few others would probably disagree!

Cheers

 

[reelectrics]

looking at designing a 200kw ground mount fed from a farm tns supply i will need to run 4 cables each protected by a 300 ma type a rcd to comply with 17th regs 100m cable to pv from isu and g59 relay .what is the problem with running one cable out to pv array and then fitting 4tpn boards fitted with rcd to protect final circuits .i will be using sma tri power20kw so 3 inverters on each 300ma rcd.your thoughts appreciated

 

[Worcester]

100m cable isn't a very long run.
Why a remote G59 relay when using SMA Tripowers? or are you going to overvoltage them so as to compensate for an undersized cable with high voltage drop?

 

[reelectrics]

g59 at isu in plant room then ugc 1m deep to array then ip56 enclosure cable designed at 1%vd

 

[Gavin A]

what is the problem with running one cable out to pv array and then fitting 4tpn boards fitted with rcd to protect final circuits

I think I understand what you're getting at... if so, then I think you'd need a single 300mA RCD at the grid connection point, rather than 4 separate RCDs on the final circuits, as otherwise the cable from grid connection point to distro board wouldn't be protected.

AFAIK you'd not then need to run separate RCDs on each circuit, though I'm not sure if 12 tripower inverters would be too much for a 300mA RCD or not - I suspect it's borderline - if so then I think you'll have to split it at the grid connection point.

 

[reelectrics]

from sma guidence only 3 inverters can be fitted on a 300ma type a rcd due to 90ma leakage from each inverter hence thats why the requirement for the four rcds ie 10 inverters .section 705 all circuits no more than 330ma on farms and nic guidence

 

[Gavin A]

from sma guidence only 3 inverters can be fitted on a 300ma type a rcd due to 90ma leakage from each inverter hence thats why the requirement for the four rcds ie 10 inverters .section 705 all circuits no more than 330ma on farms and nic guidence

fair enough, I don't think I've ever done more than 3 tripowers on a circuit, so I've learned something today, thanks.

eta - I've worked out where I went wrong there as well, thinking the earth leakage would be split across the 3 phases, but effectively the reverse is true.

 

[reelectrics]

At design stage but curious which method other installers are complying with regs and rcd issues on ground mount systems .