Outside electrics advice please

[benthebuilder]

Hi, I have searched through the forum and just can't quite make my mind up as to what I am doing is the right way so I am just hoping for an answer on here. My apologies if I'm asking something which has been asked many times before. I have to run some power to a garden shed to supply a socket and a light. Then also some power to an avery for lighting and heating. What I propose to do is run a length of 6mm T+E from the RCD protected CU to a new CU in the shed. I'm not yet sure of the power of the heating in the avery so I will have to decide on the MCB for that later on. There is a spare way in the house MCB which I will run out of to the shed possibly protected by a 40A MCB. From the new CU in the shed, I will have circuits for shed socket (16A MCB), shed and garden lighting (6A MCB) , avery lighting (6A MCB)and avery heating (MCB unknown as yet)(4 circuits). I want to keep the avery and garden lighting seperate. The T+E will be underground and I will run it through that blue water pipe that mains water is now fed through and put some warning tape around it. I appreciate any advice you can give me on this. I haven't worked with SWA before, so as long as it's safe, I would prefer to use T+E. It's all being buried a long way underground, I've seen the channels dug for me in the garden and afterwards these channels are being concreted over as it forms the edge of the patio area. Cheers, Ben

 

[another_sparky]

As you say, you cant make up your mind which way to do it.

I've used pvc (buried in plastic conduit and concreted over-much as you describe.) But that was only for running lighting cable to a lamppost in my own garden.

But for outside power to a shed/garage etc, I'd use SWA.

If you're not confident about earthing to the outer strands- you could always use 3 core SWA ( Red black Yellow) - (( or brown blue yellow))

and then turn the yellow into an earth. ( making sure you identify it as the earth cable with green/yellow sleeving( or tape)

Why are you using a 40 amp mcb . if you're only running 16 amp sockets and 5amp lights?

 

[benthebuilder]

I was going to use a 40A MCB because of the heaters for the avery. I know I will have to wait until I find the wattage of these heaters before finalising which MCB to use, but I can imagine the heaters drawing quite a bit of power, if not, I will use a smaller MCB. I guess I'm hoping to use T+E rather than SWA because I haven't worked with SWA before and am not 100% confident of using the glands etc where as I know where I stand with T+E. Plus the fact I have a great big reel of T+E left over from a previous job! Also, as far as the earthing requirements go, would I have a problem by connecting the earth from the T+E into the earthing block in the house CU? I've read about discrimination between the house and what would be the new CU in the shed. I'm pretty sure it's not a TT system im dealing with here. Thanks for the reply!

 

[another_sparky]

The TT is Earth return via earth electrode. So you should be able to see whether you have an earthing rod somewhere near your CU.

But irrespective, the earth from the TWE, still goes into the main earthing block.( terminal)

you could use TWE to do the run to the shed. if you are confident that the buried cable will be safe from mechanical abrasions.. and the ends of the pipe dont chafe the cable.

 

[benthebuilder]

Thanks, Another Sparky, that was what I needed to know! I am quite happy that the cable will be protected, it's going to be buried a metre underground and with concrete on top and to be extra sure, I will leave a diagram of the cable run with the house owner which could be passed on to any new owners should he ever sell the house. Thanks for your advice, very much appreciated! Ben

 

[breezer]

you could also put a note at each end of the cable saying where it goes, and how it gets there

 

[benthebuilder]

Good thinking, Breezer, I will do that. Cheers!