Shed electrics from garage electrics?

[TheOriginalTableLeg]

I plan to get a shed sometime this year so as to be able to move a lot of stuff that currently fills my garage.

In my garage (attached to my home) I have a direct feed from the main CU to a second smaller Cu in the garage which has an Rcd and 2x mcbs (one is for the light and the other for the sockets). The cabling from the main Cu is in 2.5mm T&E.

My shed will go behind the read of the garage approx. 2m from it.

Is it at all possible to utilise the wiring from the garage to supply the shed as well or would the shed require its own circuit to the main Cu?

I only plan to have 1x light in the shed and one double socket.

???

 

[PrenticeBoyofDerry]

With 2.5mm cable you are restricted to a maximum CCC of 27A. That is providing there is no derating of cables with regards to method of installation.
Thermal insulation and containment such as trunking/conduit will decrease CCC.
What load are you expecting to draw?
I would suggest that 2.5mm would be updated to 4.00mm.

 

[TheOriginalTableLeg]

Thanks for the reply.

With regards to load do you mean in the shed alone or combined with the garage?

 

[PrenticeBoyofDerry]

Thanks for the reply.

With regards to load do you mean in the shed alone or combined with the garage?

The combination of both, as this would help determining your distribution cable from house.
As stated previously I would say 2.5mm cable is a bit too low on the rating side.

 

[TheOriginalTableLeg]

I think that you're probably right about the loads.

I think i'll have to resign myself to the fact that it'll be too much work to run a 4mm or even 6mm cable from the Cu through the house and the garage then out into the garden and to the shed.

i'll give it some more thought.

Thanks anyway.

 

[TheOriginalTableLeg]

Oh I should have said that my garage circuit in 2.5mm is on a ring to its own MCB in the main Cu in the house in case that makes any difference to your suggestions.

Would your suggestion be to replace the 2x 2.5mm runs from the main Cu with a single or double 4mm?

If so, could this be run to the garage Cu (40a RCD plus 1x 32 sockets and 1x 16 lighting) and then retain the current 2.5mm ring for the garage and add 4mm from the garage Cu to run out to the shed?

 

[Iggifer]

I very much doubt the garage is supplied from a ring circuit. You wouldn't feed a submain from a ring circuit.

It's most likely a radial. What size breaker is the garage cu in the main cu 20a?

 

[ban-all-sheds]

I very much doubt the garage is supplied from a ring circuit. You wouldn't feed a submain from a ring circuit.

Depends what kind of person was responsible for it in the first place.

 

[Iggifer]

I very much doubt the garage is supplied from a ring circuit. You wouldn't feed a submain from a ring circuit.

Depends what kind of person was responsible for it in the first place.

very true. but then I suppose a ring supplying one item wouldn't really be a ring per se, it would just make parallel conductors

 

[PrenticeBoyofDerry]

Oh I should have said that my garage circuit in 2.5mm is on a ring to its own MCB in the main Cu in the house in case that makes any difference to your suggestions.

It would yes, if this is correct.
Are you saying this pair of 2.5mm cables are fitted directly from the house CU to the small garage CU at the main isolator?
Therefore making this distribution cable in reality 5.00mm?

Would your suggestion be to replace the 2x2.5mm runs from the main Cu with a single or double 4mm?

Read more: //www.diynot.com/forums/electr...arage-electrics.351807/#2645293#ixzz2IPJFq2Ht

This would depend on the answer to my previous questions above?

If so, could this be run to the garage Cu (40a RCD plus 1x 32 sockets and 1x 16 lighting) and then retain the current 2.5mm ring for the garage and add 4mm from the garage Cu to run out to the shed?

What size protective device is house CU?
Again the load desired or proposed would be an advantage if known?

 

[briwire]

Unless you are using your shed for anything major, in normal use your load should be well within the rating of the 2.5mm supply. I would treat your shed and garage as you would with two lightly used rooms in your house, and pick up the shed lights from the garage lighting, same with the sockets.

Make sure that the wiring between the two is well protected in galv conduit, trunking, SWA or unistrut. You are protected by the RCD in the garage but when you have it tested just make sure that the earth loop impedance in the shed is adequate to disconnect the supply in the event of a fault.

If you had all the lighting on, it should only take around 1 amp. If you then use your sockets for things like a lawnmower, drill etc, there shouldn't be a problem.

 

[TheOriginalTableLeg]

Thanks all for the replies and the information.

 

[TheOriginalTableLeg]

Hello again all.

I am revisiting this as I am now in a position to get the shed (well I will once the snow has gone!!!).

To add some information to that detailed above as a check has revealed I gave some incorrect information.

I have checked the garage wiring.
It is a single length of 2.5mm T&E, run from the main house CU on its own 16a Mcb and on the RCD side of the CU (its a split Cu).

I have one spare slot in the CU on the Mcb side which currently has a 40a Mcb.

In the garage currently I have 4x 4' Flouro tubes and 2x double sockets.

The garage sockets are used occasionally for battery charging, a tumble drier and the odd electrical tool.

As far as running cable for the shed if it were connected in some way to the garage wiring it would be a lot simpler since running a new cable to the shed from the main Cu would means passing through the full length of the loft then somehow through the garage flat roof for the full length then down inside the garage before passing out through the back wall to the shed.

Connecting to an existing socket in the garage would mean extending a socket only 2' to reach the back wall.

Based on this is it advisable to replace the 2.5mm feed from the main Cu to the garage with something heavier either 4mm or 6mm?

If that were the case could the existing garage wiring be utilised to supply the shed? Currently the garage has a 'garage' Cu which has an RCD and 2x Mcb's (32a with the sockets and 6a with the lighting), or would I need to use a different Cu with at least 3 slots so the shed could be on its own Mcb with its own cable?

Appreciate the help as always.

 

[Taylortwocities]

My replies below

Hello again all.



I have checked the garage wiring.
It is a single length of 2.5mm T&E, run from the main house CU on its own 16a Mcb and on the RCD side of the CU (its a split Cu).

So, not a RING then!
It would be better if it were not on the RCD side. The SWA doesn't need an RCD. And you have an RCD in the submain CU in the garage. Pointless.

I have one spare slot in the CU on the Mcb side which currently has a 40a Mcb.

Eh?? This does not make sense. All sides of your CU will be MCB sides.
Do you mean RCD side? Post a picture of your house and the garage CUs

In the garage currently I have 4x 4' Flouro tubes and 2x double sockets.

The garage sockets are used occasionally for battery charging, a tumble drier and the odd electrical tool.

The total load that you can run is 16amps, the value of the MCB in the house CU. The tumble dryer will be 10-13amp. Plus the lights. That's your total load right there. The 16A MCB at the house end could be 20amp maximum, subject to EFLI and VD limits - these will need checking with calibrated test equipment before the MCB is changed.

As far as running cable for the shed if it were connected in some way to the garage wiring it would be a lot simpler since running a new cable to the shed from the main Cu would means passing through the full length of the loft then somehow through the garage flat roof for the full length then down inside the garage before passing out through the back wall to the shed.

Connecting to an existing socket in the garage would mean extending a socket only 2' to reach the back wall.

Whatever. Can't even begin to imagine the layout.

Based on this is it advisable to replace the 2.5mm feed from the main Cu to the garage with something heavier either 4mm or 6mm?

It depends on teh total load. You havent said what you are runnignin the shed - MIG welder? Engine hooist, hydroponics plant, hot tub???????
What's the total load????

If that were the case could the existing garage wiring be utilised to supply the shed? Currently the garage has a 'garage' Cu which has an RCD and 2x Mcb's (32a with the sockets and 6a with the lighting), or would I need to use a different Cu with at least 3 slots so the shed could be on its own Mcb with its own cable?

Yers, of course the shed COULD be powered from the garage. But the TOTAL load cannot be more than 16amp - the value of the MCB right at the house CU.
I don't know who installed the garage CU but it is is TOTALLY POINTLESS having a 32amp MCB for the garage sockets if the MCB at the house (feed) end is only 16amp. The upstream fuse must always be bigger than the downstream fuse. You may as well replace that 32A MCB in the garage with a rusty nail, because its always going to be the 16A mmcb in the house that will pop first, cutting off the total supply to the garage. And the house too, if its an earth fault.

 

[securespark]

You don't have any discrimination between the garage CU and the supply MCB.

The supply MCB is 16A. The garage MCB is 32A.

On your current 2.5 supply cable, you can up the 16A breaker to 20A or 25A (if the manufacturer makes one: only a few do). But you need to make sure things like voltage drop & earth loop will fall within spec before you do this.

This will give you a bit more capacity to allow a little extra for the shed. You have not said what the load will be in there but if it's just a light & socket for light or occasional use, you could limit the supply to the shed to 5A via a fused spur.

EDIT:

TTC. The supply cable is T&E, not SWA.

I think he has a "16th" board with RCD on some MCB's and not others. So, the 16A garage circuit is RCD-protected, the spare 40A MCB is on the other side and is not.