Can I wire a light circuit like this?

[Tim84]

It's for my shed, not sure if this is an acceptable wiring setup so I've put together a quick diagram for you guys to advise.

Two gang switch running two lights (one inside, one PIR) and no need to continue the circuit. I've presumed it's OK to Choc block in the switch as per the diagram. No earth terminal in the plastic back box.

Untitled

• Tim84
• 21 Apr 2014
• 1

 

[sparkwright]

Looks good to me.

 

[EFLImpudence]

Yep.

 

[PrenticeBoyofDerry]

Looks okay to me.

 

[Tim84]

That was quick, thanks both*. Couldn't see any diagrams like this so wasn't sure if I was missing something obvious! Off to the shed I go...

* edit: thanks all three!

 

[PrenticeBoyofDerry]

There is a diagram similar in Wiki, if you exclude the cable to next supply.
//www.diynot.com/wiki/Electrics:Single-way-lighting, scroll down to using terminal block within switch.

 

[Tim84]

There is a diagram similar in Wiki, if you exclude the cable to next supply.
//www.diynot.com/wiki/Electrics:Single-way-lighting, scroll down to using terminal block within switch.

Oh yes, I see it now - for some reason I didn't notice this before, must be the extra cable that confused me! The block is even in the switch like mine too.

Wired it all up last night so we'll see how it goes once I've had the supply run to the shed...

 

[PrenticeBoyofDerry]

Be aware if this a new circuit there is a requirement for building controls to be notified and regardless of that it is important that the work is inspected and tested in compliance to BS7671.
//www.diynot.com/wiki/Electrics:Part-P

Test order
Continuity of protective conductors
Ring final circuit continuity
Insulation resistance
Polarity (dead)
Polarity (live - confirm after energising system)
'Lectrode (if applicable and if using a loop tester))
Earth eault loop impedance (Including prospective short circuit current)
Devices - incluidng RCD and functional switching

 

[Tim84]

Yep, it's a new light circuit and socket circuit running off a garage CU. The hookup back to the main CU in the house will be done by an electrician at which point he'll test the light and socket circuits I've installed in the shed and then certify them (or tell me they are crap)

I've got four double sockets on 3.5mm t&e so I've not run them as a radial circuit, just linear. Do you forsee this being an issue? I have a fifth double socket on its own supply from the garage CU for ease of wiring, again this is like a spur straight off the CU rather than radial.

The main issue with running a return from socket four is there is no room in the mini trunking I've used.

 

[ericmark]

The method you show is standard in USA and clearly will work OK. However in the UK we tend to use the ceiling rose rather than switch box as our junction box there are some good reasons.

1) Loop impedance is lower as less cable used.
2) Permanent line available at light for when emergency lights or fans are used.

There are also some advantages with using switch as junction box specially when powering outside lights when using double pole switches means no neutral - earth fault once light is switched off making it simple if water gets in you just switch off and all other lights are OK.

As already said you should test. The problem with new circuits from old consumer units is getting RCD protection for buried cables.

As to Part P rules unfortunately no one has defined a "new circuit" so it up to you to decide. New circuit is considered all after an new protective device but it is considered a fused connection unit (FCU) does not count as new protective device and a MCB is really the same as a fuse so most houses today have just two circuits each supplied by a different RCD. Or does it? It would be for the courts to decide and unless your work causes a death unlikely the courts will get involved.

However insurance is another story and any work not to standard they can refuse to pay out should damage happen as a result.

There have been argument galore on what electricians should tell DIY people on forums. The simple fact is 99% of DIY people will not test and inspect as laid down in the regulations and 90% of the time they get away with it.

Personally I have done a risk assessment and to give advice is likely to produce a safer installation than to say nothing as most DIY people will carry on what ever we say.

So all I can say is good luck.

 

[Tim84]

Thanks ericmark and PBoD, very useful posts.

These are 100% new circuits being run from a new garage CU in a new shed fed by a new SWA cable fed from the 18 month old CU in the house.

I'm paying the electrician to come out anyway as he's running the SWA cable so his testing and certifying as new circuits is a given as I'd be pretty upset if my wiring killed someone (or me!) or burnt down my new shed!

The cable runs are all short so I'm happy with the lighting arrangement - as you've said I can isolate the outside PIR light circuit using the switch too which was the main aim of putting in a 2G switch.

I'd like all of the work to be certified and notified - my only slight concern is the existence of the shed as it shouldn't really be there without planning permission due to proximity to the boundary wall. We'll see what happens when the electrician sends off the paperwork!

 

[PrenticeBoyofDerry]

All your socket outlets will likely require to be RCD protected, the best method to avoid nuisance trips within the house from trips associated with the shed, would be to have the distribution circuit to the shed in SWA and either on an MCB or a RCBO that is not protected by RCCB in the house consumer unit, then depending on the device used at the CU, you can have a Garage consumer unit that either has RCCB or RCBOs protecting sockets (MCB at house) or a just a standard non RCD protected board (RCBO at house)

 

[Tim84]

We're going for a dedicated MCB in a spare slot on the house CU with the SWA feed attached.

In the Garage CU the sockets will have one breaker and the lights the other breaker.

That's as technical as I get, I'm trusting the electrician to get it right...

 

[JohnW2]

As to Part P rules unfortunately no one has defined a "new circuit" so it up to you to decide. New circuit is considered all after an new protective device but it is considered a fused connection unit (FCU) does not count as new protective device and a MCB is really the same as a fuse so most houses today have just two circuits each supplied by a different RCD. Or does it? It would be for the courts to decide and unless your work causes a death unlikely the courts will get involved.

It is true that the legislation does not define "new circuit", such that there is scope for debate/discussion and disagreement. However, I suspect that the majority of electricians (and, hopefully, well-informed courts, not that they will ever be asked to decide!) would probably consider the 'common sense view' to be that, in this context, 'a circuit' starts at a 'primary' over-current protection device of the installation (e.g. an MCB, RCBO or fuse in a CU). If new wiring goes all the way back to such an OPD (whether the OPD was previously present or not), that probably counts as 'a new circuit' - but if it doesn't, then it probably isn't a 'new circuit'. No doubt some will disagree

There have been argument galore on what electricians should tell DIY people on forums. The simple fact is 99% of DIY people will not test and inspect as laid down in the regulations and 90% of the time they get away with it. ... Personally I have done a risk assessment and to give advice is likely to produce a safer installation than to say nothing as most DIY people will carry on what ever we say.

As you are aware, I totally agree with that view/approach, and it is some senses nice (but in others senses rather sad) to be able to say so, and to put that sort of approach into practice, without being 'jumped on'! ... and that applies to advice given by non-electricians as well as electricians

Kind Regards, John