TT SYSTEM

[lostthewill]

HI ALL, BIT OF ADVICE NEEDED.
LARGE PLOT OF LAND. IN 1 CORNER STANDS A BUILDING WITH A 3 PHASE HEADER (NOT SURE YET IF IT'S TN OR TT).
THIS HAS A TP+N SWA FEEDING ANOTHER BUILDING COMPRISING OF A SMALL CORNMILL, A SMALL FLAT AND @25 STABLES. FROM THE CORN MILL THERE IS A SP SWA FEEDING THE BUNGALOW.
FROM WHAT I CAN DECIPHER FROM THE REGS (TRIED NICEIC HELPLINE, GUESS WHAT? 20 MINS OF GREENSLEEVES LATER...) I WILL HAVE TO 'SPIKE' EACH BUILDING SEPERATELY.
SO, THE SWA FROM THE SUPPLY WILL BE EARTHED AT THE SUPPLY END ONLY. THIS WILL TERMINATE INTO A 3 PH DIS BRD. THE DIS BOARD WILL THEN FEED SINGLE PHASE TO THE CORNMILL/FLAT, 1 PH TO THE STABLES AND ANOTHER TO THE BUNGALOW.
SWA TO STABLES INTO A CU. SWA EARTHED AT SUPPLY END ONLY. CU TO BE SPIKED.
SWA TO BUNGALOW DITTO.
CORN MILL/FLAT CU NEXT TO 3 PH DIS. BRD.
DO I SPIKE THE DIS BRD TOO?
OBVIOUSLY EACH CU WILL HAVE RCD TO PWR + LTG. WITH 100Ma MAIN SW
IS ANY OF THIS CORRECT???

 

[Steve]

WHY ARE YOU SHOUTING?

Are you an electrician?

Each SWA should be earthed at its origin, but the other end must be terminated into plastic so its not exposed and the earth cannot be exported. Each building should have its own earth rod, especially the stables where consideration should be given to livestock.

This is quite a major installation, are you sure you're up to it?

I dont fully understand what you're going to do in each building, perhaps if you typed in small letters, and described the equipment and protective devices and cables used for each supply, we'd be more helpful to you.

 

[Lectrician]

Or if the supply is TN-S, there is no real issues.

If it is TN-C-S, then aslong as the earth conductors (likely the steel armour) between buildings is sized accordingly, it can be used for main equpotential bonding of the services in the buildings that are sub-mained.

I would avoid a TT install, even in parts, where at all possible.

 

[lostthewill]

sorry about the shouting

this is the 1st time i've come across a TT system and just need clarification. i'll try to be a little clearer with my 'explanation'.

there is a 3 phase and neutral supply entering a stone building. from here a swa enters another building. this building is sub-divided into 3 parts. (cornmill, a flat and the stables)
in here i intend to fit a 3 phase distribution board.
this, in turn , will feed 3 seperate consumer units.

the 1st cu for the stables will be fed via swa. the cu will have a 100Ma main incomer, with 30Ma rcd protection to power and lighting circuits. the cu will be plastic. the swa feeding this will be earthed at the main db only.
sockets, switches and light ftgs will be ip 56 rated. wiring in pvc conduit.
an earth spike will be fitted near to this cu.

2nd cu is adjacent to the main db. fed via DI meter tails. this will also be of plastic construction. wiring / rcd as above. c/w spike.

3rd cu to be fed via swa is sited a short distance away in the bungalow. swa to be earthed at main db only. plastic cu with spike. rcd protection as above.

the main DB will also be spiked.
the 3 phase supply to be fitted with TP+N sw fuse.

does this comply?
p.s. certification will be issued on completion.
yes, steve, i am a sparks, nic approved, just a little fluffy around tt sytems

regards

 

[Spark123]

Fair enough 100mA TD RCDs at the consumer units, but how is the armoured cable feeding to it protected (ADS)?

 

[lostthewill]

Fair enough 100mA TD RCDs at the consumer units, but how is the armoured cable feeding to it protected (ADS)?

300 Ma rcd

edit: 300mA rcd

 

[Spark123]

300mA TD RCD

 

[sparkyspike]

Turbo diesel?

 

[lostthewill]

pedantic

 

[Spark123]

Not really - it is called discrimination. Put the wrong type in and your faulty kettle can take out the whole lot

TD = Time delay or as you see it written nowadays, Type S for Selective

 

[lostthewill]

300mA TD RCD

typical bloody cumbrian! that's where i'm originally from actually. lived in seaton. family in workington, whitehaven .....

 

[Spark123]

Poor you

 

[lostthewill]

even worse down here in yorkshire

 

[Steve]

even worse down here in yorkshire

OY!

We''l have less. Well ok at least Doncasters alreet.

 

[ColJack]

don't forget that the stables will come under section 705, and the cornmill may have it's own set of rulse not explained in BS7671 as it's a potentially explosive atmosphere.. check with the relavent bodies to see if it is..