Supply to cabin

[Sb8389]

Hi guys,
I'm going to put a cabin on my garden which is going to be made into a hair salon.
im starting to confuse myself on how to run the supply in to the cabin.
current arrangement in house is a dual RCD consumer unit (plastic)
TNCS supply.
in the cabin there will need to be power for maybe 3 lights
3 heaters at probably around 2000w each
a water boiler supply
and probably a radial circuit for general power

i was was thinking to run a 10mm 2 core armoured supply terminating it into adapt box and running a 10mm T&E to the consumer unit
part of it will be buried
now I know I shouldn't be exporting the PME and should put the cabin on its own TT system
im just curious on best way to connect this back up at the house avoiding discrimination of RCDs
there will also be extraneous parts within the cabin ie water supply (would any bonding be required even though it's bonded within the house) probably a silly question.
i appreciate your thoughts but it's something I have not come across before.
any thing else you need to know just ask.

 

[jackhammerJIM]

Have a read through the special location section of the regs

 

[Midwest]

This subject is posted weekly, some might say daily. Perhaps you should search the subject first, as per below, and answer some of your own questions.

 

[telectrix]

groan..

 

[d.l.rob]

10mm cable on a 40A breaker should be fine for the loading you require.
Unfortunately, you WILL HAVE to TT your cabin as it has a mains water supply that will require a main protective bonding conductor from the TT supply. This is because it could introduce separate earth potential and if there is a fault on the supply neutral, all of your water heaters, taps etc would become live at mains voltage, giving your customers the hair style they would not want!
As for the discrimination, up to you! If I was quoting this job I would give you the two options of either that way. Or taking a new supply from the mains to a new C.U in the building. OBV not on 10mm tho .

 

[Darkwood]

10mm cable on a 40A breaker should be fine for the loading you require.
Unfortunately, you WILL HAVE to TT your cabin as it has a mains water supply that will require a main protective bonding conductor from the TT supply. This is because it could introduce separate earth potential and if there is a fault on the supply neutral, all of your water heaters, taps etc would become live at mains voltage, giving your customers the hair style they would not want!
As for the discrimination, up to you! If I was quoting this job I would give you the two options of either that way. Or taking a new supply from the mains to a new C.U in the building. OBV not on 10mm tho ��.

That is an option, not necessarally the only one though, the house has a perfectly good earthing system, why would you side step it for a less reliable method?

@The OP - you are not allowed to extend your PME system, I think you meant extend your equipotential zone which you are allowed to do, 2 very different things in deed

 

[Sintra]

10mm cable on a 40A breaker should be fine for the loading you require.
Unfortunately, you WILL HAVE to TT your cabin as it has a mains water supply that will require a main protective bonding conductor from the TT supply. This is because it could introduce separate earth potential and if there is a fault on the supply neutral, all of your water heaters, taps etc would become live at mains voltage, giving your customers the hair style they would not want!
As for the discrimination, up to you! If I was quoting this job I would give you the two options of either that way. Or taking a new supply from the mains to a new C.U in the building. OBV not on 10mm tho .

10mm might not be fine depending on installation method and length of run. Also the water main could be plastic and therefore wouldn't need bonding.

 

[Leesparkykent]

10mm cable on a 40A breaker should be fine for the loading you require.

Unfortunately, you WILL HAVE to TT your cabin as it has a mains water supply that will require a main protective bonding conductor from the TT supply. This is because it could introduce separate earth potential and if there is a fault on the supply neutral, all of your water heaters, taps etc would become live at mains voltage, giving your customers the hair style they would not want!
As for the discrimination, up to you! If I was quoting this job I would give you the two options of either that way. Or taking a new supply from the mains to a new C.U in the building. OBV not on 10mm tho ��.

do you have a crystal ball? How do you know the length of run.
A

 

[Dave OCD]

In fact using a plastic pipe to feed the water supply to the cabin would be much simpler all round.

 

[Sb8389]

10mm might not be fine depending on installation method and length of run. Also the water main could be plastic and therefore wouldn't need bonding.

Installation method is clipped direct and buried for about 5 metres, total run is about 10metres.
The water supply will be in copper so i will have to bond the water. TT apears to be the way then?

 

[d.l.rob]

Ok fair enough. I would personally put it on a TT if it has extraneous conductive parts though.And yeah I agree, volt drop, length of run and installation method of cable should be taken into account of course. Guess I just assumed it was a small garden size

 

[Octopus]

Installation method is clipped direct and buried for about 5 metres, total run is about 10metres.
The water supply will be in copper so i will have to bond the water. TT apears to be the way then?

Why???

 

[Leesparkykent]

What KW is the water heater?

 

[Octopus]

Hi guys,
I'm going to put a cabin on my garden which is going to be made into a hair salon.
im starting to confuse myself on how to run the supply in to the cabin.
current arrangement in house is a dual RCD consumer unit (plastic)
TNCS supply.
in the cabin there will need to be power for maybe 3 lights
3 heaters at probably around 2000w each
a water boiler supply
and probably a radial circuit for general power

i was was thinking to run a 10mm 2 core armoured supply terminating it into adapt box and running a 10mm T&E to the consumer unit
part of it will be buried
now I know I shouldn't be exporting the PME and should put the cabin on its own TT system
im just curious on best way to connect this back up at the house avoiding discrimination of RCDs
there will also be extraneous parts within the cabin ie water supply (would any bonding be required even though it's bonded within the house) probably a silly question.
i appreciate your thoughts but it's something I have not come across before.
any thing else you need to know just ask.

Why add unnecessary connections?

 

[Sb8389]

i suppose i could have a word with the plumber and see if he can put a plastic supply in.
Would this mean i dont have to TT the cabin then
The water heater will be around the 3.5kw area.

 

[Octopus]

How is the plumber going to run the pipe? Will that be partly above ground?

 

[Sb8389]

Yea partly above ground across the house then buried to the cabin..
Murdoch how would you say im best connecting the armoured into the consumer unit (the consumer unit is on an external wall)

 

[Octopus]

Yea partly above ground across the house then buried to the cabin..
Murdoch how would you say im best connecting the armoured into the consumer unit (the consumer unit is on an external wall)

I would terminate the outer shealth of the swa into a Wiska box but then continue the inner cores through the wall directly to the CU.

 

[sparksburnout]

Why would you use copper pipe to run a water supply to this cabin??? Does the plumber like hard work and risking burst pipes??

 

[Octopus]

Water pipes should be buried at 600 / 800 mm down - not sure how anything above ground is going to be OK unless you want it to spring leaks every winter!

 

[telectrix]

corrected that for you.

 

[jackhammerJIM]

When you said cabin i assumed steel container . What will said cabin me made of ?

 

[telectrix]

logs, wattle and daub.

 

[sparksburnout]

3 x 2KW heaters? Going to be pretty hot in there are you sure it's a salon??

 

[telectrix]

one assumes the heaters have thermostats. these are silly little knobs that women max up and when they're out, real men turn them down.

 

[davesparks]

For the tiny amount extra it will cost you can get 10mm three core SWA and you will have a main bond at the new outbuilding in the form of the extra core, this will be sufficient to bond the extraneous parts at the outbuilding and use the PME Earth of the installation.

The chances of a buried water main being anything other than blue MDPE pipe these days is pretty rare, but if they do use copper then it will make a lovely little earth rod to supplement your PME Earth connection.

To achieve good discrimination you could feed the submain via a KMF style switchfuse.

 

[Dave OCD]

For the tiny amount extra it will cost you can get 10mm three core SWA and you will have a main bond at the new outbuilding in the form of the extra core, this will be sufficient to bond the extraneous parts at the outbuilding and use the PME Earth of the installation.

The chances of a buried water main being anything other than blue MDPE pipe these days is pretty rare, but if they do use copper then it will make a lovely little earth rod to supplement your PME Earth connection.

To achieve good discrimination you could feed the submain via a KMF style switchfuse.

Metalclad to Amd 3 of course.