Wiring in stables - advice please

[sidekick]

I have a job to wire a brand new stable block.
x 1 tack room with x 1 strip light and x 2 2g sockets.
x 4 stables with x1 strip light in each with switches outside doors
x 4 bulk head lights under canopy.
Temp DB already in tack room supplied by armoured cable from DB in house off 32A RCD protected MCB.
Temp DB also currently supplying power to 3KW horse walker and 1kw septic tank.
Additional requirement for Stable block - Room containing shower to wash off horses.

Assuming cable size correct for, or can be changed to correct size for a higher rated MCB.
Is it correct as follows : 6A MCB for septic tank supplied in armoured cable - 20A MCB for horse walker supplied in armoured cable - 6A MCB for lights supplied in standard pvc cable in plastic conduit - 16A MCB for sockets supplied in standard pvc cable in trunking - Can the shower be safely in corporated into the board as all the above already looking at a 50A MCB in house and 10mm armoured cable. Will TNCS from house cover earth requirement and will 300ma RCD be a must. First post so go easy as all work so far been domestic. Good advice appreciated.

Cheers
Sidekick

 

[Des 56]

Is there a metal grid in the floor of the horse washing room ?
If there isn't TNC-S is not recomended

Adding up the mcb sizes and coming up with 50 amp does not total the actual loading

Calculate the required load to find what your total demand is,then check if cable is sized correctly,taking into account cable length

Siize the mcb at source for suitability with cable size and loading

Advise having a good read of the big red book section 705 for quite a lot of particular requirements for these installations,

horses have been known to chew nicely on plastic conduit so be careful with design

 

[sidekick]

Thnkyou,
Sorry about delay - been away.

The power source is comming from the main house which is TNC-S but there is no metal grid in any floor in the stable yard.
Whats the best way round this?

Without the shower the loading for lights, horse walker and septic tank is 4528w - 19.7A plus now x 4 2g sockets one for freezer on permanent and one for well used kettle. Others as and when horse clippers etc. 32 to 37A additional if shower instaled.

Run from house 12m so should be looking at 10mm cable (or 25mm with shower)

Stiil not happy about uprating mcb in main DB. Should it have seperate 100A DP 30ma RCD at house to supply board in stable block?

Will run rubber shethed cable (protection against amonia in horse urine) through galvanised steel conduit to suply lights and switches.

Client does not want conduit on outside so run down inside of stables with back outlet box through wall to feed switch.

Realise i am very green here but all work to date domestic so may be in a little deep here.

Main concerns - TNC-S supply ( Any need to install earth rod)
High demand from house csu
Is shower possible or a step too far
Is rubber sheathed cable ok in steel conduit.
Need 300ma RCD at stable board

 

[Guest123]

Hi.

Have you assessed the existing demand of the house and current stable area to make sure the suppliers equipment (fuse) can deal with it???

Personally I would make the stables a "TT" system due to conductice parts present and the presence of 4 legged animals.

Standard 13A socket outlets need 30mA RCD protection, any other circuits need 300mA.

I'd be wary of having anything within reach of a horse inside a stable....explain to them which they would rather a bit of conduit showing on the outside, or.....a dead horse!

 

[sidekick]

Thanks Lenny
House already has two sets of tails supplying 2 dist boards.
One for all lights (x 30), sockets x 27, u/floor heating bathroom and kitchen and x4 smoke detectors.
Second for Cooker, boilerimers heater and another 11 kitchen sockets.

Second already has a 32A mcb supplying temp board in stables and already supplies horse walker 3kw
and septic tank 1kw.

One of the sockets also may need to be seperated from the others as I belive when clipping horses the socket for power also needs to be 300ma rcd protected.

I can sort the earth rod out at the stable end but how does this link into the house TNC-S system
I assume just connect as normal but additional earth from the Earth rod with the earth systems seperated at the stables

 

[Guest123]

Hmmm sounds like there is quite a large load there already....what size is the DNO fuse???

how does this link into the house TNC-S system
I assume just connect as normal but additional earth from the Earth rod?

It doesn't....

Basically if it's an SWA then the armour is glanded and bonded to earth at the house end but NOT at the stable end i.e glanded into a plastic enclosure.

If it's a 3 core SWA then the 3rd CPC core needs terminating and making safe NOT connected to anything. The only earth is the earth provided by the earth rod by the stable.

The only thing then is the use of RCD's as the Ra (electrode resistance) may be too high for a 300mA RCD (167ohms) max. So you may need to use a 100mA S type for your other circuits aswell as your 30mA for socket outlets.

 

[AA410]

Something you want to think about is rats and mice they love pvc cable i had a job in a stud years ago the twin - earth cable i took out was bear copper with mice atached .

 

[sidekick]

Something you want to think about is rats and mice they love pvc cable i had a job in a stud years ago the twin - earth cable i took out was bear copper with mice atached .

Thanks.
Think the steel conduit will take care of the light circuit and although trunking will be used in the tack room for sockets, a further socket at the other end of the yard may have to be run in steel conduit also.

....what size is the DNO fuse???


Basically if it's an SWA then the armour is glanded and bonded to earth at the house end but NOT at the stable end i.e glanded into a plastic enclosure.

If it's a 3 core SWA then the 3rd CPC core needs terminating and making safe NOT connected to anything. The only earth is the earth provided by the earth rod by the stable.

The only thing then is the use of RCD's as the Ra (electrode resistance) may be too high for a 300mA RCD (167ohms) max. So you may need to use a 100mA S type for your other circuits aswell as your 30mA for socket outlets.

100A or 80A assumed but to be confirmed.

Will seperate the two earth sytems but the current stable csu is metal.

If 300ma RCD cannot be used, is that not against the 17th regs?

 

[Guest123]

If 300ma RCD cannot be used, is that not against the 17th regs?

Not if it's smaller i.e 100mA, as you are affording a greater level of protection than prescribed by the regs.

 

[poppypiesdad]

I have never had to use anything other than pvc conduit in stable blocks ,take care where you route them and away from equines,rodents are your biggest problem but the stable cat usually keeps them at bay..

 

[sidekick]

Not if it's smaller i.e 100mA, as you are affording a greater level of protection than prescribed by the regs.

Makes sense- thanks

Regarding the metal csu - I suupose i could just not connect the armour to it.

But looks like too much demand on the DNO fuse.
Is the only way round that for a seperate supply to the stables?

I have never had to use anything other than pvc conduit in stable blocks ,take care where you route them and away from equines,rodents are your biggest problem but the stable cat usually keeps them at bay..

These stables are a new build row in stone. Client wants a light switch outside each door. Providing I can get them far enough away from the door, where would you sight light switches without a run of conduit down the side of each door and would pvc not be prone to horse chewing?

 

[Guest123]

Makes sense- thanks

Regarding the metal csu - I suupose i could just not connect the armour to it.

Esiest way out of this is to disconnect the SWA from the CU and install a polybox between the SWA and the CU. Gland into this and just pass L+N straight through into the CU.

 

[sidekick]

Esiest way out of this is to disconnect the SWA from the CU and install a polybox between the SWA and the CU. Gland into this and just pass L+N straight through into the CU.

Cheers - That will be easy enough as just done exactly that for one where couldnt get swa cable in.

But looks like too much demand on the DNO fuse.
Is the only way round that for a seperate supply to the stables?

Any suggestions on the problem with demand on the DNO fuse?
Seperate 100A isolator switch in house or new supply to stables is all I can come up with????

 

[electro]

Hi excellent thread (just rated it 5*)


I would apply for a new supply to the stables and use an earth spike, also I would replace the metal clad board with a plastic one to save on a type S 100ma switch.

Regards

 

[sidekick]

Hi excellent thread (just rated it 5*)


I would apply for a new supply to the stables and use an earth spike, also I would replace the metal clad board with a plastic one to save on a type S 100ma switch.

Regards

Thanks Electro,
Sorry could you clarify what you mean by " save on a type S 100ma switch "

Would this still need a new supply if no shower was required??