Farm supply not tt

[Simon-0116]

Hi I live on a farm with livestock but we are on pme earthing, electric board guys say not many farms on tt around here do I still need to fit 300 ma main switch. Zs is 0.80
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[JD6400]

To be honest , unless you are a sparks with the required test gear , do not do it your self .
But depending on your bonding arrangements , ie : earthed metal grids , then you need to be TT and have a max 300ma RCD upfront regardless .

 

[Simon-0116]

Even if on tn cs with or without livestock. Not seen any farms we go to with. 300 ma rcd up front new or old

 

[JD6400]

705.411.1 , (iii) = 300ma RCD
And as for TT , I have yet to come across a livestock holding that meets the criteria not to be .


Edit ; Don't forget it used to be 500ma before the 17th came out .

 

[LeeH]

What's the science behind this?

I can see the logic not having TNCS but why not TNS?

 

[Welchyboy1]

What's the science behind this?

I can see the logic not having TNCS but why not TNS?

Tns is not a problem, would still require upfront rcd

Due to the rural areas farms are normally in, underground supply cables are not usually practical and usually supplies are from overhead lines

Hence tns is rare

 

[Engineer54]

I think you need to study the do's and dont's, with regard to livestock farming regulations where PME supplies are concerned. Generally, if livestock quarters with concrete floors are present, then those concrete floors must have a rebar grid that is permanently bonded to the PME's installations MET. If there is no grid present then livestock housing/milking areas must be on a TT earthing system...

Any up-front 300mA RCD needs to be an S type, for discrimination purposes, or you'll find 30mA downstream RCD's taking out that up front unit in fault conditions!!

 

[Clive P]

Hi,
Thanks for that E54, worked in most places but never farms. Everyday is a learning day.

Regards.