Working on Maggie's Farm.

[Evans Electric]

I have some work coming up on a farm in Warwickshire .

Thing is , farms in Birmingham are ,to say the least, few on the ground so perhaps a little advice from any Forumites who are used to working in this land of sheep dips and cowpats.

Due to this lack of Farmland in Brum I tend never to look at that section of the Regs, until now that is. First problem I see is that a TN-C (PME) "shall not be used " . Yet the DNO have installed a 100A SP PME supply . This is in a meter housing about 100Mts down the road with a sub-main laid by the farmer coming in to one of the units. Looks like a 50mm SWA.

Theres a couple of jobs there , my regular builder is building a house for them (at top of window height at the mo) so I have the electrics for that.

Also the farmer wants some low bay 400w HQI s in the Lambing Shed and a socket. . ( Its like living within an episode of the Archers!!!)

Also BRB says RCDs must be DP . Am I correct in saying that all RCBOs are SP ? (I don't use them because my loop tester knocks them out ) ( And no, I'm not buying another one!!!)

What I'm thinking is :-

1. Speak to the farmer about new dist.Bd at incoming position. ( No choice really)

2. Disconnect the incoming earth and install rods for TT.

3. New house will be TT also .

Dist.Bd: I'm thinking of a 3 way split load, 300mA main sw with at least one way for the house, then 2 X 30mA splits for the rest .

Farm is made up of :-

A general unit (with main dist.Bd )

Unit with tractor etc parked.

Lambing Shed open ended.

Large Chicken coup .

Control panel to cess pit.

Temporary caravan until house is built.

New house

Just realised , this is the dreaded "Exported Earth" don't let Steps know FFS !!

Blimey this goes on a bit !!

 

[Zeespark]

Deke, don't quote Me, but you may need a 500mA RCD at the front end (if I am incorrect I apologise in advance). You can get DP RCBO's, but they take up 2 modules/ways in a distribution board (Hager do them).

AndyGuinness

 

[NozSpark]

Deke, don't quote Me, but you may need a 500mA RCD at the front end (if I am incorrect I apologise in advance). You can get DP RCBO's, but they take up 2 modules/ways in a distribution board (Hager do them).AndyGuinness

Zee

705.411.1 (BRB) states...

30mA for final circuits 32A and under

100mA for final circuits over 32A

300mA for all other circuits

Also as Deke says TN-C system "shall not be used",,,, but does that go for the initial sub main?

 

[Sidewinder]

Deke,

PME it properly, rod at each board and anywhere else that is useful, local steel framed buildings etc.

 

[Zeespark]

As per the caveat in My answer to Deke's question Noz B-)

AndyGuinness

 

[NozSpark]

I did see that Andy,

I just thought that it'd be better to get it down in black and white as to what the regs actually say,,, for future reference

 

[Zeespark]

Thats fine bud, I have spend a few hours today going through section 5 of the BRB anyways.

AndyGuinness

 

[Evans Electric]

I find this Reg : confusing TBH.

Sidey if it says "TN-C shall not be used " I don't want to be PME ing it everywhere but changing it to a TT system but the Reg: does not continue with any more information .

Does it mean the supply cannot be TN-C or does it mean the rest of the farm wiring must not be TN-C as in those concentric cable /combined N/E / Home Office permission jobs . Of which I've only ever worked on two systems of that ilk. Don't even know what they're called.

 

[Sidewinder]

Deke,

Think about the difference between TN-C-S & PME.

I am proposing PME.

 

[Evans Electric]

Sorry for delay, had to go wash up.

You're right I'm getting mixed up.

So let me get this right .

TN-C uses the same conductor for N and E and is prohibited under ESQCR anyway , within consumer's installation, hence me getting confused with Reg: 705.411.4 Page 183.

So this farm has a TN-C-S supply which means a seperate earth conductor will be used through the farm. ( as opposed to a combined one)

Now I'm happy with that but Sidey has confused me again !!!!!!

Sidey , two things:-

1, Although I still refer to PME ( because I'm a dinosaur) , it changed its name in the 15th to TN-C-S so unless I've totally lost it, they are the same :C

 

[NozSpark]

Is PME ok on a farm?

Just thinking about it, if you lose your neutral on the suppliers side then all your neutral current will still pass to earth through all those rods you've installed,,, the voltage gradient radiating from the rods could still be enough to kill livestock?

The RCD's shouldnt trip because all the neutral current is still going through them to the N-E joint in the head

 

[Evans Electric]

I see where your coming from with that Noz , I would be fitting a 300mA RCD as a main switch which should cover faults within the property .

I'll log in later , missus is whinging .

 

[NozSpark]

Still won't trip with a lost supply neutral though

 

[steptoe]

guys,

I dont want to be a big wash on this,

#but we are now going into the realms of stuff that may or may not be reasonable to make public on an open forum due to the implications it could have on people doing this without adequate knowledge on the implications it could have on the earthing systems in practise at the premises at any given time,

also, it is not a given that this sort of system could be implemented in all situations anyway,

we need to be careful of how this is protrayed for future learners.

---------- Post Auto-Merged at 22:05 ---------- Previous post was made at 22:04 ----------

Still won't trip with a lost supply neutral though

why.?

 

[steptoe]

Is PME ok on a farm?Just thinking about it, if you lose your neutral on the suppliers side then all your neutral current will still pass to earth through all those rods you've installed,,, the voltage gradient radiating from the rods could still be enough to kill livestock?

The RCD's shouldnt trip because all the neutral current is still going through them to the N-E joint in the head

proper Ra testing would prove this not to be the case (within reasons of acceptability) if installed properly.

---------- Post Auto-Merged at 22:08 ---------- Previous post was made at 22:07 ----------

So come on then StepsPME = TNCS (or not) :slap

now now canoey,

surely you are taking the proverbial here,,,,,

 

[steptoe]

I have said this many times,

PME MUST be TN by its nature,

TNCS is NOT always PME, even though it may be called such, seldom is it a true PME system.

---------- Post Auto-Merged at 22:15 ---------- Previous post was made at 22:15 ----------

Just a clear answer from the rod god would be good ROTFWL

can I quote that to Aggie? :slap

 

[batty]

In the old days they would not give you an earth on a farm things have changed though.

 

[Evans Electric]

I was thinking about that too Batts, I remember that. There used to be a similar thing with petrol stations , would not give you a PME supply to a filling station as I remember . I think there was a concern with the fuel tanks in the ground being a better earth than anything off the supply network, so any fault currents were expected to go down via thhe fuel tanks instead of the mains.

 

[SPECIAL LOCATION]

Well......

Just read, correction... tried to read some of this......

BUT.....

having just got back from a family birthday party....

GuinnessGuinnessGuinnessGuinness:Blushing

All I can suggests is.....

This blokes instructions...

:C :C

 

[Evans Electric]

Go get your head down , Specs.