Garden lighting... PME from the house or TT from the shed?

[Mattja]

Expecting I'll have to put it on the TT but here's the situation...

PME from the house connecting to the armour plus one core of outgoing SWA. Intending to terminate the SWA at a wiska box on back of the shed (outside), connect the armour to the cpc again and that earthing ends there (some would say overkill but honestly it's not much effort with those gland plates wiska makes), this box will be filled up with gel when I'm done with it. From here the L+N go directly into the back of a tiny shed CU/DB, which is on TT.

Now customer has just asked to have lighting going round the garden starting from the shed, but doesn't want to get the shed too 'busy'. I'm going to be taking power to these lights with SWA, and obviously I'm not going to have two separate earthing systems present in a single wiska box!! Rather I'm thinking I'll take the garden lighting out from the other end of the back of the shed (out of arms reach) if it needs to be on TT with the shed.

So my question is, am I going to have to say "sorry, but I need a few more boxes in here" or can I have the garden lighting leave the shed through the same box as the incoming supply and on the PME (except where it's inside the shed going to the switch ofc)?


Again, thinking it has to be the TT, but I don't have my book with me, yes I'm a right ---- for that, tin hat on!

 

[Richard Burns]

I would tend to terminate the SWA for the outside lighting into the CU you are installing in the shed. There would be a cable leaving the CU and going outside, hardly too busy, especially if they have asked for the supply to come from the shed.
I would say that you might need to check that there are not other power supplies running around the garden on the TNCS supply in which case you may get two different earthing systems in close proximity.
The armour for the incoming SWA and the incoming cpc must be separated from and inaccessible to, the electrical equipment from the shed.
If you want to use the PME supply for outside lighting I would start from the house.

 

[Mattja]

Thanks Richard, nothing running around the garden already

Yes the hole for the cables to pass between the wiska box outside and the CU inside (right behind each other) will be sealed up, as in I'll make the hole just big enough to fit the cables I want through (shed wall about 1.5 to 2 inches thick), and silicone around it.


EDIT: misread your comment, thought you were saying take the PME to the shed CU, blame the heat.

Could take it straight out the CU for the lighting, but I think customer would object to an ugly black SWA sticking out in the shed, even more than a extra box inside and out, where everything else is white conduit. No Pleasing some people.

 

[Octopus]

Without wishing to sound difficult how and where does this customer think they are going to control this lighting?

 

[Pete999]

Thanks Richard, nothing running around the garden already

Yes the hole for the cables to pass between the wiska box outside and the CU inside (right behind each other) will be sealed up, as in I'll make the hole just big enough to fit the cables I want through (shed wall about 1.5 to 2 inches thick), and silicone around it.


EDIT: misread your comment, thought you were saying take the PME to the shed CU, blame the heat.

Could take it straight out the CU for the lighting, but I think customer would object to an ugly black SWA sticking out in the shed, even more than a extra box inside and out, where everything else is white conduit. No Pleasing some people.

Take the SWA straight to the Metal CU in the shed from under the floor, no unsightly box on the side of the shed, take the lighting from the metal CU via the same routing no boxes required= less cost to you and your customer

 

[Mattja]

@Murdoch understandable! He requested a switch on the side of the shed, I know it's a bit strange. Being fair to him it is a pretty small garden that he intends to pave/artificial grass over, lights already either side of the house door, the shed right next to the house, and the new lights starting the other side of the shed. So not that inconvenient I guess.

@Pete the boxes on the outside are hidden away (shed sits about a foot and a half from the house (to side of shed) and about the same distance from garden wall behind it. It's what's showing inside he's a bit peculiar about. That's why I'm not taking the SWA straight from the CU (I agree makes much more practical sense), and instead feeding through the conduit to another exit point, assuming I can't exit behind the CU and use the PME that's in the box outside there from the incoming supply.

 

[Nigel]

Does the shed need to be TT’d?

 

[Dalimo]

If not too late, perhaps run a 10mm 3 core SWA to the shed....you then have a 10mm if needed for any extraneous conductive parts and you won't have a difference in earth potential if you run the lights from the house end.

 

[Dave OCD]

Oh no,SpongeBob Earthpants could turn up on this thread next !!

 

[davesparks]

Why do you want to create a separate earthing system for the shed?

Is it a metal shed or does it have extraneous parts in it?

What size cable are you installing for the submain?

 

[Toneyz]

I would tend to terminate the SWA for the outside lighting into the CU you are installing in the shed. There would be a cable leaving the CU and going outside, hardly too busy, especially if they have asked for the supply to come from the shed.
I would say that you might need to check that there are not other power supplies running around the garden on the TNCS supply in which case you may get two different earthing systems in close proximity.
The armour for the incoming SWA and the incoming cpc must be separated from and inaccessible to, the electrical equipment from the shed.
If you want to use the PME supply for outside lighting I would start from the house.

Just don't tell Bob