Wiring in Consumer Unit in garage with 2 way lighting source

[benzas]

Hello all,

I need some advice wiring in a consumer unit into my garage (with 63A RCD, 2 x 6A MCB and 1 x 32A MCB). I have read the sticky of 'wiring diagrams for lighting circuits' but still need help.

Current Wiring:
An armored cable goes from the house to the garage. It is on the same circuit (30A) as my boiler, extractor fan and a set of twin sockets (previous owners wired it this way. I would rather have boiler on separate circuit). It then runs to the garage where it is wired into a set of sockets in the garage as well as the lighting in the garage (2 lights, 2 switches). Finally, it also powers a single external light which has two switches, one in the house and one on the outside of the garage. As such the armored cable contains, red, black, blue and yellow wires.

The system works but I am changing all the internal lights in the garage to fluorescent battens as well as planning to add a second outdoor light to illuminate the garden in the dark (on the same ring as the other outdoor light).

As the wiring for all this also powers my boiler (annoying) I decided a sensible thing to do would be to wire in a consumer unit in the garage so that I could work on the electrics in the garage without having to turn off my boiler (there's snow outside at the moment). The plan was to wire the armored cable into the consumer unit. The outputs would then be the garage sockets on a 32A MCB, the internal garage lights on a 6A MCB and the outside lights on a second MCB so they could all be worked on or shut off idependently.

So Far:
I've wired the cable from the house into the consumer unit (the red and black wires anyway). The garage sockets are wired in and work, the internal garage lighting is wired in an works.

The Problem:
What I can't work out how to do is wire in the external lighting to run through the consumer unit. I'm sketching out the circuit diagrams but without determining which wire runs from each switch to the lights etc, it will be difficult. If there is a way with the wires I have coming into the garage (red, black, blue, yellow) to wire in the consumer unit to the outside lights, that would be great.

Many thanks in advance.

 

[sparkydude]

Sadly there is no way of confirming what you have without testing it. if they were all just fed before then they MAY have used red as live blue as neutral and not used the yellow . bare core being sleeved with green/yellow sleeving.

But this is only a guess . You need to follow the cable and draw what you have in order that we can confirm or deny this is what you need to do .

Nick

 

[benzas]

@sparkydude

Yeah I kind of figured I would need to map everything. I've mapped everything in the garage and the light switch in the house. All I now need to confirm is whether the red, blue and yellow wires that are attached to the switch inside the house are the ones which come out red, blue and yellow from the cable that goes into the garage.

I was hoping not to have to do a major re-wiring job but it looks like it's going that way. I'm definitely going to have to re-wire the lights and switches in the garage as they're a mess.

 

[Robin0577]

If I've read your post correctly, you have a two way light switching system with one switch at either end of your armoured cable, is that right?

If so, then something really horrible has been done I'm afraid and I can't think of an easy way to reinstate it so that it complies. If the armoured cable does indeed link the two light switches then it would seem likely that they've taken a live supply to the switch at the house end (presumably from the red core) and used two other cores (probably the yellow & blue) as the strapping wires and the final one (presumably the black) as neutral.

If it has been done that way then it was kinda dodgy in the first place even if it did work and will most likely need a significant re-think.

Can you confirm if my guesswork is correct please, before we start speculating on ways to sort out the mess?

 

[bernardgreen]

If so, then something really horrible has been done

I can't see anything wrong with the 4 core cable having two strappers, a permanent live and a neutral provided the provision of the earth to the garage is adequate and fit for purpose.

 

[benzas]

@Robin0577
I think your description of the use of the wires is correct. I'm going to cut power again today and run some continuity tests to check if the colours going into the switch in the house match those that appear at the other end of the armoured cable. I will post back results

@bernardgreen
Worryingly there is no separate earth that comes through the armoured cable. I have attached the consumer unit earth to the metal shielding/protection of the armoured cable in the vain hope that this is grounded at the house end. Otherwise, I fear an earth rod or new cabling may be required. One of the main issues is I cannot find where the armoured cable enters the house. It may go out below ground level from inside the cavity wall.

I will report back later after continuity testing everything I can get my hands on. Thanks so far for everyone's help and suggestions

 

[bernardgreen]

The earth wire is the most important.

 

[benzas]

@bernardgreen

You're absolutely right. I've just ordered an earth rod and clamp from screwfix and some 16mm earth wire. I will wire these directly into the consumer unit when they arrive.

 

[Robin0577]

@bernardgreen

I wouldn't see anything wrong with the arrangement if the whole cable was part of a lighting circuit only, but a few things worry me in this situation, where the same permanent live and neutral appears to be part of a socket circuit and/or submain to the garage.

How is the switch supply at the house end derived? Is it properly fused down or is it simply attached to the red core of the armoured, which is in turn fed directly from a 30A socket circuit? Or is it supplied from a separate lighting circuit, making the neutral in the armoured shared?

If an RCD protected CU is added at the garage end, then the neutral for the outside light is going to have to be connected to it's supply side of the RCD, because the live supply to the two way switching must be derived from the house end of the cable...

 

[benzas]

Well I ended up re-wiring the entire garage to make things much simpler and using current colour BS wiring. The only thing I haven't changed is the armoured cable running from the house to garage (I REALLY don't want to have to change that).
I've also wired in a new earth rod in the garden which runs into the consumer unit with 16mm2 earth wire.
The live from the house feeds the consumer unit and the 1 way (L1) on both 2-way light switches (internal to garage and external) come off MCB's in the unit. Commons are linked as are the the 2 way (L2) terminals on the switches which then feeds the lights, which come off nice junction boxes. These return neutral to the CU which is then linked back to neutral in the house through the armoured cable. Simple right.

It was all working, but now, the inside 2 way light switch trips the RCD (not MCB) in the consumer unit. I'm assuming something has gone wrong in one of the junction boxes and will investigate this weekend. Everything else works including the outside light from the outside 2 way switch so just to not use the internal light switch until I can fix it.

I may ask for advice if I can't work it out.

Many thanks for all for suggestions.

 

[Robin0577]

Which side of the garage RCD is the neutral of the outside light connected to?

If the live supply comes from the house side of the RCD then so must the neutral or you will have an imbalance...

 

[Taylortwocities]

It always makes me smile when somebody with a 30ma RCD-protected garage CU feels it necessary to connect an earth spike with 16mm earth cable. WHY??
The maximum earth current will be 30 milliamperes. A bit of telephone wire would be more than enough.....

 

[ban-all-sheds]

I decided a sensible thing to do would be to wire in a consumer unit in the garage

Are you aware that you needed Building Regulations approval for that?

The garage sockets are wired in and work, the internal garage lighting is wired in an works.

What testing did you do before and after energising?

I have attached the consumer unit earth to the metal shielding/protection of the armoured cable in the vain hope that this is grounded at the house end.

That is unbelievably and criminally inadequate.

I've also wired in a new earth rod in the garden which runs into the consumer unit with 16mm2 earth wire.

Is it safe to assume that you didn't test that?


Please engage the services of a competent electrician - you have neither the skills nor the right attitude to be doing electrical work.

 

[ban-all-sheds]

It always makes me smile when somebody with a 30ma RCD-protected garage CU feels it necessary to connect an earth spike with 16mm earth cable. WHY??

Because they don't know what they are doing?

 

[benzas]

@Robin0577
The neutral of the outside light is connected to the protected (garage) side of the consumer unit. I will try wiring both live and neutral through a junction split with it going to the CU and the 2-way light separately.

@Taylorwocities
You're absolutely right that the maximum earth current is 30mA from the garage, but the earth spike is also connected to the earth of the armoured cable which also feeds the house (which doesn't have an RCD) adding additional earth capacity to the house (as I'm not convinced how good the earth in the house is). I do have a tendency to slightly over-engineer though.

@ban-all-sheds
Yes I'm aware I need Building Regs approval and a Part P qualified, registered sparky will be checking everything once complete.