Feeding a Shed Cu from the main CU

[GLENNSPARK]

no...i`d better not.....will go major will this..lol....

 

[Guitarist]

I think people may be keeping out of this one Glenn.....

 

[Deleted member 26818]

It appears that this installation may well be classed as Agricultural/Horticultural.
As such, I would suggest a perusal of Section 705.
The circuit supplying the shed will require a minimum of 300mA RCD protection.
The socket-outlet circuit will require 30mA RCD protection.
The shed will most likely require bonding, as it's an extraneos-conductive-part.
If the earthing system is TT, then the disconnection times will be 1s for distribution circuits and 0.2s for final.

 

[Guitarist]

Do you still keep horses (as you have a tac room)? Where is the tac room fed from, and as what type of supply?

 

[robbo777]

I think people may be keeping out of this one Glenn.....

Why's that then?

 

[Guitarist]

Why's that then?

You started by saying that you were sending a supply out from a main CU to a shed, which most people can easily relate to. Now it appears that the main CU is already in an outbuilding itself and your "shed" is a massive aluminium conductor in direct contact with earth. You haven't told us anything about your main earthing arrangements or whether there are still horses in the vicinity.
I merely meant that the situation seems more complex than the OP suggested and that most people would keep out of this thread without seeing your exact setup. No disrespect meant at all.

 

[robbo777]

This seems to be getting a little confusing so I'll start again with the exact set up.


Firstly there is no house.
The tac room has its own supply from the main supplier which is a TNCS system
there is 1 socket in the tac room and 1 light in each of the stables so 9 lights in total, the light switch for each stable is on the outside of each stable out of reach of any horse and in an IP66 enclosure.
the lights are fed by 1.5mm singles in 20mm PVC conduit over 2m high and inside
There is a 30mA RCD in the CU protecting all circuits

The shed
I want to put 3 x double sockets in here with 2 x flourescent lights.

I will run 4mm singles in conduit to an external junction box where I will come from there in 4mm SWA to the 2 way CU in the shed
I will feed this by a 32A breaker in the main CU and use the main RCD to protect this circuit
I will of course bond the shed.

how does this look?
I appriciate the help with this

 

[jase]

will it be a 3 core SWA? make sure the SWA is bonded, and i think you may have to run a 10mm earth back to the MET to bond the shed/lorry

 

[Deleted member 26818]

To start with, use of a TN-C-S supply appears to contavene both BS7671 and ESQCR.
Is the main supplier aware that the installation is using their PME connection?
If you intend bonding the shed, as the supply is TN-C-S, a 10mm² conductor will be required, or the shed will have to made TT.

 

[Guitarist]

Thank you for clearing that up robbo. How far is the lorry/shed from the main CU? Just wondering if 4mm will be adequate as you are feeding it from a 32A supply. Have you done the VD calcs?
Also, regarding the bonding, what spinlondon said.

 

[robbo777]

Thank you for clearing that up robbo. How far is the lorry/shed from the main CU? Just wondering if 4mm will be adequate as you are feeding it from a 32A supply. Have you done the VD calcs?
Also, regarding the bonding, what spinlondon said.

The shed is just under 30m away from the main CU I have looked at table 4D1 Ref Method B and 4mm will carry 32A the voltage drop on that was 4.47% (10.5v) which is within the 5% drop allowed.
I can always Reduce this to 20A as there will never be that kind of power going through it, all he has in there is a chop saw, table saw and a few battery chargers and these will never all be being used at the same time.

I will do that with the bonding then and take a 10mm back to the MET

Many thanks

 

[Guitarist]

Have you allowed for the fact that your conduit cables are rated differently to your armoured in your calcs, plus did you say there will be several running together in the conduit, hence temperature factors? Just thinking aloud as it is an assessment job...

 

[robbo777]

Have you allowed for the fact that your conduit cables are rated differently to your armoured in your calcs, plus did you say there will be several running together in the conduit, hence temperature factors? Just thinking aloud as it is an assessment job...

I hadn't no, thanks for pointing that out. i will use a 20A in the main CU.

Many thanks

 

[robbo777]

I hadn't no, thanks for pointing that out. i will use a 20A in the main CU.

Many thanks

Which I was going to use in the first place as I thought it was a bit close but someone mentioned in one of the earlier posts that I could go 32A but they wouldn't have known to take the other factors into consideration either.

I bet you have quite a vivid image of this installation now thank you for all of your comments.

 

[Guitarist]

I feel like I know it well :smiley2:
Hope all goes well with the assessment