sub main

[empress]

incoming house 100amp domestic supply TNCS/PME
looking to run a 63amp sub main in 25mm SWA 10m out to an outside block shed to feed a ice energy heat pump system and a couple of sockets on a radial and a couple of lights.
shed has its own water supply.
the spec fo the heat pump demands a 300ma rcd so will need 2 DBs to feed each service..
was thinking of splitting the swa in a plastic enclosure using henley blocks to feed both boards?
not much load on the heat pump in normal use but is does have boast element which peaks at 26amp .
ice energy tell me that if the boast kicks in then there is something wrong with the set up as it is inefficient.
mains positionin house is cramped and would struggle to fit a metal clad switched fused isolator one with a handle but was wondering if i could get away with a small metal clad 2 gang DB and 63amp mcb?
later on might site a small 1 bedroom log cabin 50 yards away from shed with 16amp radial power, lights and a 7.5kw shower,would you power it from the new shed submain or get a new supply?
finally could i get away with this submain as an extension of the house PME supply or do i need an earth rod on TT at the shed?
elfyn

 

[not clever]

but was wondering if i could get away with a small metal clad 2 gang DB and 63amp mcb

Thats what I use but you'll be needing a 4way db (100amp main switch + the mcb is 3 ways).

the spec fo the heat pump demands a 300ma rcd so will need 2 DBs to feed each service..

Use a standard dual rcd board & change one rcd for a 300mA...or....normal split load board & site a 300mA rcd remote to the board for the individual circuit that requires 300mA rcd.

finally could i get away with this submain as an extension of the house PME supply or do i need an earth rod on TT at the shed?

Me I tend to TT outbuildings but it's up to you.

 

[empress]

Thats what I use but you'll be needing a 4way db (100amp main switch + the mcb is 3 ways).

Use a standard dual rcd board & change one rcd for a 300mA...or....normal split load board & site a 300mA rcd remote to the board for the individual circuit that requires 300mA rcd.

Me I tend to TT outbuildings but it's up to you.

cheers ,yep sorry i was including the 100amp main switch as taking 2 ways hence 2 ways left for mcbs.
changing the dual rcd and sticking with one DB would save a few bob and work.

would you extend to the log cabin on this submain.
the main house will have less load than average ie no electric showers,cooker is gas.just the usual demand thats left
hot water and heating all heat pump .
is it possible to split the submain via henleys in an enclosure in the shed and carry on to the log cabin in the same 25mm SWA and have both units on one main 63 amp isolator fed from house mains position or does it have to have a seperate isolator in the shed before going out to the log cabin .
i'm not bothered if both are isolated at the same time but is it within regulations.
obviously the submain is protected but is it acceptable?
elfyn

 

[jbec-john]

Me I tend to TT outbuildings but it's up to you.

As Do I

 

[not clever]

was thinking of splitting the swa in a plastic enclosure using henley blocks to feed both boards

You could I suppose, but if you are trenching from the house to the block shed anyway, I'd go the extra expense on 25mm (might be lower csa but need to calculate it) 2 core swa & run in a separate sub main from the house to the log cabin from it's own isolator at the house.

 

[electricAl]

Empress, as you described the outbuilding as being supplied by the house`s PME & it has extraneous conductive parts ("its own water supply") then by definition you`ll have to TT it - otherwise adopt special measures re: Main Bonding of water service (at least)

So, effectively its logical to TT the outbuilding, & of course ensure you`re not importing the equipotential zone of the PME (earth SWA at supply end only etc)

Is the water service supplied from the house or independently?

 

[ryanryan]

Me I tend to TT outbuildings but it's up to you.

do you just run in a live and neautral, and earth via a spike only?

 

[not clever]

do you just run in a live and neautral, and earth via a spike only?

I use 2 core swa & use the armour as cpc (only connected to suppliers earth at house end) & terminate the armour at the outbuilding end to an insulated adaptable box or cu.
Then use a rod & 10mm green/yellow as mec connected to the outbuilding cu's met.