Lighting Circuit

Peppa Cig

Hi, we have a light switch feeding an outside shed for lighting purposes.

The feed from fuse box shows a Hager trip switch with rating shown in photo. I was wondering does this allow some knowledge folk to determine the max load in watts on this lighting circuit?

We are hoping to extend lighting feed from shed into a log cabin. I appreciate it won’t power electric showers etc. But would like to understand what load could (in theory) be on the whole light circuit.

thanks

10-10-20

Is the log cabin getting sockets anyway?

Perhaps you aren't planning to, but you can't power an entire log cabin off the lighting circuit, it needs it's own sub-board taken off the main residential board.

Peppa Cig

no sockets, just lights

whizbang

Can you post a pic of the cable currently going into the shed, and whatever the first thing it connects up to..

2011

https://www.boards.ie/discussion/2058260758/lighting-circuit

From the picture it looks like the shed lighting circuit is protected by an MCB rated at 10A. Therefore the maximum loading should be somewhere close to 10A, let's say 9A to give a margin. So in terms of power that would be 230 x 9 which is around 2000W (or 2kW). Now that we have low wattage LED type lights available that is a lot of lights! So there should be no issue supplying lighting for 2 sheds once suitable light fittings are selected.

For use within the sheds I would suggest something like this:

https://www.screwfix.ie/p/reeve-twin-2ft-led-batten-18w-1650lm-220-240v/960pp

As these ^^^ are only 18W each the 10A MCB could be used for up to 10.

As always it would be best to employ the services of a qualified electrician to install these units.

Peppa Cig

https://www.boards.ie/discussion/comment/119546042#Comment_119546042

Perfect - Thanks!!

serox_21

"I appreciate it won’t power electric showers etc. But would like to understand what load could (in theory) be on the whole light circuit."

Maxim power for that MCB would be 2300W. 230V x 10A

If it's only ligths(LED bulbs) there won't be any issue.

Peppa Cig

Thanks to all for replies and for confirmation on max load that could be applied to that circuit.

Given the load limitations I’ve decided to bite the bullet and run a new SWA cable back to the “fusebaord” in the house. This will future proof the accommodation without limiting the type of appliances and load on the circuit.

Appreciate all the input - thanks 👍

2011

^^^ This is best practice but will cost quite a bit more. Good luck with it.

Doolittle51

Running power to outbuildings can be a bit of a minefield.

Open to correction here.

The cable from your fuseboard to your shed should be fed from an RCD protected circuit. Then you should have a sub board in the shed feeding the various circuits there. All circuits should be RCD protected.

There are a couple of different approaches when it comes to earthing. It is sometimes recommended to install a new earth rod for the shed sub board and not use the earth from the main fuseboard in the house. It really depends on the fault disconnection times and earth loop impedance.

Peppa Cig

What size armoured cable should I bury for electricity/Electrican.

1.5/2.5/4 or 6mm? (Happy to future proof but I guess 6mm is overkill).

what is the benefit of 4 core over 3 core?

Thanks!

Doolittle51

3 core will do. Size depends on the length of the cable run and the design load.

Peppa Cig

Thanks for reply.

45m run.

Load for usual domestic use appliances e.g washing machine, kettle, tumble dryer, maybe electric heaters.

Doolittle51

Thats a pretty big load so. Could be close to 6kW with a couple of heaters, dryer and washing machine all on the go.

6mm SWA on a 32A circuit would be fine. Volt drop is about 8 volts, so well within design limits.

Are you burying the cable? It would be best to get a REC out to have a look & make sure he's happy with the route etc.

Peppa Cig

Just a follow up to let you know what we did in the end following advice from electrician.

Ran 10mm2 SWA cable underground from house to out building (65m) . Cable is connected to main house fuse board on a dedicated 63 amp RCD circuit breaker switch.

Cable into a new sub fuse board in this outbuilding on a 63 amp circuit breaker with a KWH meter. Double socket in outbuilding from sub fuse board.

Feed from this new sub fuse board via SWA into accommodation building (10m away) on a 63 amp RCD breaker. Fed into an existing fuse Board in the accommodation building to supply lighting and socket circuits.

sorry if my terminology is not correct.

thanks for your help!

kirk.

Don't connect the swa from main board to a RCD

That would be a basic mistake

2011

I would feed the supply from an MCB in the main board. This would be rated at no more than 32 amps.

The cable would have to be sized to suit the long run and load. I would install a sub board in the shed which would provide RCD protection for local circuits.