Adding sockets and lights in my garage - wiring sense check please

[paullieo]

Hi all,

I'm going to amend some of the wiring in my garage to add 2x double sockets (1 w/ USB), and also add some LED two-way lighting.

The power is on its own ring from the CU (20A RCD). However, the power comes in to a fused double light switch, and wanted to check my plan is safe/in regs etc.

First question, is whether it's safe to pull the electric from this fused double light switch? See attachments below.
- switches currently control the garage sensor and internal lightbulb



Second question is then, does my wiring plan work for this purpose? Red = new parts to add. Black = old parts.
- The current uPVC conduit line that I'll connect to a junction box currently powers a fused single socket, which powers a fridge/freezer, so I'd assume this is already 2.5mm.
- The second uPVC conduit line powers a sensor light outside the garage, and a switched single lightbulb, so would assume this is at least already 1.5mm.
- The thick bars indicated uPVC conduit as they'll be running from the garage eaves 1m down from the roof-line, so just some protection for the cable.
- One socket in new non-USB double socket will be used for fridge freezer. Other sockets likely used for charging phones / tools / power tools etc.



Thanks very much for your time!

 

[LeeJC]

I would think that you'll need to reduce your protection current by some to meet regulations. 32Amps is going to be too much for all your cabling in the Radial manner you're wiring it.
If you have the option of using the device labelled fused double light switch as switched fuse in-line or switched no fuse then I would do the following.
Drop the CU Breaker to 16 Amps, wire it through the 'fused double light switch' without going across the fuse, take it to your socket outlets
Take another feed into the fuse (I would go with 1 Amp fuse fitted for your lighting load) and run that into your lighting system.

However............ I'm not as experienced as many on here, so there are going to be a myriad of other ways.
Also if the 16A Breaker you fit is RCD protected you'll lose lighting if the sockets go.

 

[paullieo]

Apologies - it's actually 20Amps - just went and checked the CU, amended original post.

 

[EFLImpudence]

Ah, ok.

It would appear that A and B are the now 20A Radial circuit and C and D go to the lights.

So, this Radial circuit can supply as many sockets as you want?

Any further lighting should be taken from the outlet of the fuse.
Your diagram does not make much sense regarding the LED lights.

 

[EFLImpudence]

Any further lighting should be taken from the outlet of the fuse.

Or, of course, another fuse off the radial socket circuit.

 

[EFLImpudence]

As mentioned above, all should be 'protected' by RCDs.

 

[paullieo]

So, this Radial circuit can supply as many sockets as you want?

Any further lighting should be taken from the outlet of the fuse.
Your diagram does not make much sense regarding the LED lights.

OK thanks - I've made a new wiring plan below also based off EFLImpudence's advice.

Or, of course, another fuse off the radial socket circuit.

As mentioned above, all should be 'protected' by RCDs.

Thanks. So use RCD-sockets instead of normal double sockets?

New wiring plan:

 

[Murdochcat]

When he says “all” he means all the lights and sockets need to be RCD protected

Is there RCD protection at the main fuseboard / consumer unit?

 

[paullieo]

When he says “all” he means all the lights and sockets need to be RCD protected

Is there RCD protection at the main fuseboard / consumer unit?

Ah ok. Yes, RCD protected at consumer unit.

 

[LeeJC]

Sorry Mate but your drawing is confusing me with the flow. This is how I would do it but it takes no account of locations of anything which is what I think you're trying to show on your diagram.
I've taken the fused connection unit spur off the last socket because trying to get 3 cables in socket 1 would be a pain, but you can take that feed from anywhere in the line between your CU and Socket 2 using a junction box if necessary (I'd personally go for a Wago Box and 3 x 3 way connectors)
The double switch in the location you've got in your drawing isn't really doing anything useful anymore. It could be useful if you were to use it as a switched supply for your sockets (avoiding the fuse as suggested before) and utilised the fusing aspect for your lighting circuit.
That would end up looking something like this.

I've not included any conduit which I think you've also put on drawing, and the fuse fitted to the light feed off your double switch I'd use 1 Amp for the light load your talking about. Also I've suggested the fused double switch might be full isolating (disconnects both live and neutral) obviously it's only switching live from the photo you provided.

 

[Murdochcat]

Ah ok. Yes, RCD protected at consumer unit.

On the basis that the circuit supplying the garage has RCD protection there is almost nothing to be gained by adding more rcd protection in the garage.

 

[paullieo]

Awesome - thanks for all your time and replies.

View attachment 312186

Will use this, thanks @LeeJC

 

[ericmark]

There are three limiting factors.
1) Cable able to take the current.
2) The volt drop.
3) The prospective short circuit current high enough to open the protective device.
You have looked at one, and even looked at RCD protection, which today for new circuits should be type A with this sign at least, old type AC no longer permitted, and cable sizes to take the current, but with any refrigeration device which is single phase you need to look at volt drop, if to much they can fail to start, inverter drives are OK as they convert to 3 phase and auto adjust for volt drop, although the regs say 5% on sockets, likely you would get away with double that, same with the 3% for lights, with LED lighting or fluorescent with electronic ballast likely you can get away with double that, however we have no idea of distances involved and likely volt drop.

The PSCC or loop impedance if measuring that way (both linked with 230 volt using ohms law) needs to ensure enough current runs with a short circuit to either rupture a fuse or trip the magnetic part of a MCB. So a B20 MCB with trip at 22 amp in fullness of time, and that will be faster that the cable heats up, but to trip in the specified time it needs with a B type 5 times the rated value so 100 amp, so the impedance (name given to AC resistance) needs to be 230/100 = 2.3 Ω with an old fuse if slightly out it did not matter, a fee milliseconds longer, but with a MCB it can be the difference between 0.01 seconds and 5 minutes, so we give it an extra 5% just in case.

A plug in tester like this will show if under 1.9 Ω but you can only really test when compete, which is a little late, to hire a meter likely will cost same as plug in tester approx £50 but will show actual reading, so you can work out what adding more cable will do.

But if you have had an EICR or got the original EIC it will have the figures, so you should know how close to the wind your sailing. In real terms as an electrician we have a good idea what it is likely to be just looking at the job, and unless we think it is going to be close call we will only measure when complete. But I can't see what you have, and been caught out before giving advice and assuming what is there.

Personally for a garage supply would want either a RCBO (RCD and MCB combined) in house consumer unit so garage fault does not trip house, or a RCD in the garage and the supply only MCB protected at the house. When we sign the installation certificate or minor works we sign that we have designed, also installed and inspected and tested, but electrical systems should be designed, not just connected up a collection of parts.

 

[JohnW2]

Personally for a garage supply would want either a RCBO (RCD and MCB combined) in house consumer unit so garage fault does not trip house, or a RCD in the garage and the supply only MCB protected at the house.

Is that because, for some reason, you think that things in a garage are more likely to trip an RCD than are things in the house?

Kind Regards, John

 

[paullieo]

Sorry for bringing back an old thread.

But wanted to pass on a thanks to those that read and responded here, it was immensely helpful. I completed this little project a few weeks ago and everything is working perfectly!

Thank you @LeeJC @EFLImpudence @Murdochcat @ericmark