Farm Mains Upgrade

[JohnW2]

The BGB says TN-C, although the regs seem to allow a TN-C system in other cases the ESQCR doesn't allow it without permission from the secretary of state. ... That isn't to say another country that uses BS7671 can't use it, that just depends on their local laws.

That's all true, but are you saying that you don't think(as I do) that the BGB (705.411.4) actually means (in practice, in the UK) TN-C-S?

After all, if it just said "TN", you would presumably take that to encompass both TN-S and TN-C-S - so does not "TN-C" also encompass TN-C-S?

Kind Regards, John

 

[westie101]

although the regs seem to allow a TN-C system in other cases the ESQCR doesn't allow it without permission from the secretary of state.

Not too sure about that statement as I can't find that restriction in ESQCR.

In fact the only connection restriction is in the case of PME (T-N-CS) which a DNO cannot connect to the metal work of a boat or caravan

 

[JohnW2]

although the regs seem to allow a TN-C system in other cases the ESQCR doesn't allow it without permission from the secretary of state.

Not too sure about that statement as I can't find that restriction in ESQCR.

If the Note to 543.4.1 of BS7671 is to be believed, "In Great Britain, Regulation 8(4) of the Electrical Safety, Quality and Continuity Regulations 2002 prohibits the use of PEN conductors in consumer's installations".

Has that perhaps been superseded?

Kind Regards, John

 

[westie101]

Ah that one.
It actually says: -

(4) A consumer shall not combine the neutral and protective functions in a single conductor in his consumer’s installation.

Which is not a restriction on the type of earthing a premises may be connected to, but a restriction that a customer cannot combine a N & E (it was also included in the earlier legislation The PME Regulations.

 

[flyingsparks]

After all, if it just said "TN", you would presumably take that to encompass both TN-S and TN-C-S - so does not "TN-C" also encompass TN-C-S?

That was my immediate thinking too, but perhaps it is only TN C installs, which as you say John, would be a bit strange considering BS7671 doesn't allow TN C within the consumers setup.

 

[RF Lighting]

At the bottom om page 183 there is a foot note

NOTE: Where a metal grid is not laid in the floor a TN-C-S supply is not recommended

Rather than not allowing the use of TN-C-S on farms, it seems the regs does not prohibit it at all.

 

[flyingsparks]

Coming back to the RCD issue, I believe the regs still want an RCD on all circuits, including submains of at least 300mA. That is why I specified the 300mA TD RCD's at the origin. - 705.411.1.(iii) Do you agree?

 

[flyingsparks]

At the bottom om page 183 there is a foot note

NOTE: Where a metal grid is not laid in the floor a TN-C-S supply is not recommended

Rather than not allowing the use of TN-C-S on farms, it seems the regs does not prohibit it at all.

Which book have you got?! Doesn't say that in my BGB 1st ammendment!!

 

[westie101]

I sense confusion.

T-NS (Corrected to TN-S from TN-C after RF Lighting pointed out my error) is the type of earthing provided by the DNO where the Neutral and Earth are separate (sort of) all the way back to the substation and the N is only connected to earth art source (the substation)
There are millions of customers (a lot of them farms) supplied by this way and there is no restriction on using it in any premises

T-N-CS is where the DNO combines the neutral and the earth as one conductor and also earths this combined conductor at multiple points, there are restrictions placed on DNOs regarding boats and caravans (which we include temporary buildings in)(4)

(4) The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat.

there are no other restrictions on the use of this earthing method. (see also my earlier post)

 

[westie101]

Sorry guys but I think some need to just stop following the book and actually understand the theory and implications before making decisions!

 

[RF Lighting]

Yes and no! Again it depends where you feel the farm installation starts and stops.

The 300mA RCD is there to prevent fire, particually due to rodent damage of wiring.

As per usual the regs leave huge holes for interpretation. If you'd rather cover your ass and RCD the whole site, then I see no reason why a 300mA time delayed RCD would not be suitable, as long as you have DP devices such as non delayed RCDs further downstream on the installation to prevent a fault taking out the entire installation.

Personally, if for example the house is supplied in SWA or MICC etc, then I would keep it off RCD, but I understand it's your name on the certificate, and therefore it's your call!

Interesting thread though

 

[westie101]

Rather than not allowing the use of TN-C-S on farms, it seems the regs does not prohibit it at all.

There is NO prohibition and there never has been, it's just practically a lot of trouble in use it where farm animals are involved.
If there was we would not be permitted to provide a PME earth to farms.

 

[RF Lighting]

At the bottom om page 183 there is a foot note

NOTE: Where a metal grid is not laid in the floor a TN-C-S supply is not recommended

Rather than not allowing the use of TN-C-S on farms, it seems the regs does not prohibit it at all.

Which book have you got?! Doesn't say that in my BGB 1st ammendment!!

Sorry I am using my red regs to save going to the van! It's a foot note tacked onto the end of regulation 705.415.2.1

 

[RF Lighting]

I sense confusion.

T-NC is the type of earthing provided by the DNO where the Neutral and Earth are separate (sort of) all the way back to the substation and the N is only connected to earth art source (the substation)
There are millions of customers (a lot of them farms) supplied by this way and there is no restriction on using it in any premises

I sense confusion too. That description sounds very much like TN-S to me

 

[westie101]

That description sounds very much like TN-S to me

OOps