Wiring a shed and pond

[Pymie]

I want to take a supply from the house via a 4 core armoured cable 2x live (L1 & L2), 1x neutral, 1x earth. L1 and L2 taken from house via RCB.
The cable will be run to the shed, L2 via a switch in the house, and terminated at a jct box. L1 will then be split into 2, 1 feed taken from the shed to supply a pond pump (continuous supply via RCB), the second feed via a timer to supply garden lights (3 off low power). L2 will be split into 2 supplies via MCB, one feed to supply a double socket, the other to feed 2 outside lights.
The reason for two supplies is so that I can isolate the shed and ouside lights from the house without isolating the pond and garden lights. Any problem with this arrangement? Do I need any additional protection in the feed to the pond and garden lights (currently (excuse the pun) an RCB)

 

[plugwash]

seems ok

i would run from a 20A dedicated cuircuit (with rcd protection either from the rcd side of the board from a seperate rcd or by using an rcbo instead of a mcb) to a 2 module grid plus box with 20A switches for the 2 outgoing lives

http://www.tlc-direct.co.uk/Products/MKK3492.html
http://www.tlc-direct.co.uk/Products/MKK4891.html
http://www.tlc-direct.co.uk/Products/MKK3702.html
http://www.tlc-direct.co.uk/Products/MKK8891.html

at the shed end i would terminate into a 4 pole isolator http://www.tlc-direct.co.uk/Images/Products/size_3/WY921E.JPG
any sockets can be run directly off this for lights i would use fused connection units fitted with a 5A fuse

the armoured cable should be sized to be suitable for the length of the run i will advise on size when given the run lenth

 

[Pymie]

Thanks for advice.
Cable length is 30m to shed and then further 10m to pond. Not sure what the power requirements for pond is but probably 600W ish

 

[ban-all-sheds]

Sounds like a borrowed neutral to me....

 

[brown-nought]

I want to take a supply from the house via a 4 core armoured cable 2x live (L1 & L2), 1x neutral, 1x earth. L1 and L2 taken from house via RCB.

The reason for two supplies is so that I can isolate the shed and ouside lights from the house without isolating the pond and garden lights. Any problem with this arrangement?

Sorry to be a pain but you cannot have a shared neutral across two different circuits.

Best option is to run two separate cables as this means there are no junction boxes etc with more than one supply to isolate.

Alternative: subject to cable sizing, fault loop imedance, earthing arrangements etc is to use the four cores for the supplies and the amour for the earth.

 

[plugwash]

but surely if they are running off a common breaker in the CU they are part of the same cuircuit

 

[ban-all-sheds]

but surely if they are running off a common breaker in the CU they are part of the same cuircuit

He's right you know.

 

[brown-nought]

Splitting hairs I know but the orginal post never said L1 & L2 were off the same supply in the house CU. It said off the same RCD (which could be a the split load CU RCD for example)

L2 is switched intended to be used as an isolator. (Isolators DP for single phases?) Its hard to isolated the neutral if its shared.

 

[plugwash]

well i presume when he says isolate evrything in the shed he means turn off functionally not isolate for maintinance

i suggested a 4 pole isolator at the shed end of teh armoured cable to provide local isolation of everything (includeing both lives) at that end

 

[brown-nought]

I'm going to correct what I wrote yesterday after thinking about it a bit more - I believe it was misleading/wrong.

L2 is switched intended to be used as an isolator. (Isolators DP for single phases?) Its hard to isolated the neutral if its shared.

Wrong - 416-01 ... isolators in TN installations do not need to isolate the neutral. Neutral isolation is only needed in TT and at the source of a single phase installation.

Burrowed neutrals - chapter 31 states final circuits need to have their own neutrals. Plugwash/Ban are right the final circuit here has its own neutral and the MCB can be used for isolation.

Obviously if you run a cable into a shed CU and then see the neutral looped out it might look odd on an inspection. However I guess if a diagram was attached and a warning notice of where to isolate was enclosed it would be ok.

Apologies for the confusion sometimes its too easy to jump into an answer without sufficent thought/verification. Wrists slapped. However I’d still personally be happier with two cables.

BN.

 

[Pymie]

Thank you people.

The single cable is a convenience thing. However the supply is being fed off of a single source (the house ring main). The isolation of the shed circuit is to allow me to switch an outside light, mounted on the shed, from the house so that I can see my way to the shed at night. It will also have the benefit of isolating the shed without isolating the pump which needs to keep going 24 hrs a day apparently. For maintenance, I can isolate from the main CU.

I think from the debate, that the principle is acceptable.

Once again thanks.

 

[breezer]

the pump which needs to keep going 24 hrs a day apparently.

it does, see this

 

[Pymie]

Once again thanks.
Time to start digging trenches and shed foundations. Am I looking forward to that!

 

[securespark]

When you've finished can you come and help me dig up a large tree stump, and lay a driveway? Cheers.