Cabling between Armoured and CU

[stevetogo]

I have recently wired up some outdoor lighting by cutting in to an existing armoured cable that runs down the side of my house and fitting a junction box (plastic, IP56) where the outdoor lighting is fed from via flex.
The armoured cable then continues from the junction box underground to my shed where I'm going to fit another small consumer unit to supply lights and sockets for the shed.
Unfortunately the armoured cable runs in to my understairs cupboard but has been chopped about 6' short of the consumer unit.

What's the best way to extend the armoured to the CU?
Could I just run the armoured cable in to another junction box and then run 2.5 T+E to the CU?
If I did this, would the armoured need to be glanded as its indoors anyway?

Finally, what size MCB would this require and would it need to be RCD protected?

 

[Spark123]

It sounds like a complete lash up. How did you continue the armour continuity through the plastic JB?
You want a lighting circuit and a supply for a consumer unit in the same cable
Armoured cable needs to be earthed properly hence the need to use correct glands.
You need an electrician to size up the job properly.
Also, this work is notifiable to your LABC under part P of the building regulations.

 

[bongos]

I have recently wired up some outdoor lighting by cutting in to an existing armoured cable that runs down the side of my house and fitting a junction box (plastic, IP56) where the outdoor lighting is fed from via flex.

Is this appropriately fused down for the lighting circuit?

What's the best way to extend the armoured to the CU?

You could use something like this.

Could I just run the armoured cable in to another junction box and then run 2.5 T+E to the CU?

Not a bog standard junction box, no. It needs to be properly terminated and the armour must be earthed.

If I did this, would the armoured need to be glanded as its indoors anyway?

What's it being indoors got to do with anything? It's not all indoors is it? The armour must be earthed.

Finally, what size MCB would this require and would it need to be RCD protected?

You have made no mention of the csa of the cable, the distance the cable runs (for volt drop calculations) or the proposed loading of the cable! Have you tested to make sure earth fault impedance levels are within spec? Are you running items with high inrush current in the shed (such as welders). Would a different curve MCB be more appropriate? Nobody would have any idea what size MCB it would require without knowing any of these factors.

As for RCD protection it depends on how several factors. It is usually wise to RCD protect at the shed end and not at the house. But this will depend on other factors usch as cable intsall menthods on other sections of the circuit.

With respect, are you sure you know what you're doing here?

Also have a look here for more info.

 

[stevetogo]

It sounds like a complete lash up. How did you continue the armour continuity through the plastic JB?

I had thought about this...
I was going to run an earth cable between the 2 earth tags on the armoured glands. I know its not ideal but thought it would suffice. I can just change the jb to a metal one.

You want a lighting circuit and a supply for a consumer unit in the same cable

I hadn't checked the regs regarding this but its good to know its a no go!! I'll scrap that then.

Armoured cable needs to be earthed properly hence the need to use correct glands.

Good point, that was a stupid question!

You need an electrician to size up the job properly.
Also, this work is notifiable to your LABC under part P of the building regulations.

Is this cos I'm adding a circuit to the CU?
As there is no existing outdoor lighting circuit, I can't do anything then cos its all notifiable under part p.

 

[flameport]

The work is notifiable for several reasons:
1. The circuit returns to the CU
2. You want to fit another CU at the other end.
3. The connections to the lights are outside.

 

[electronicsuk]

It sounds like a complete lash up. How did you continue the armour continuity through the plastic JB?

I had thought about this...
I was going to run an earth cable between the 2 earth tags on the armoured glands. I know its not ideal but thought it would suffice. I can just change the jb to a metal one.

Although that would work, it's frowned upon to gland into plastic boxes while relying on a banjo for earth continuity. If you used a piranha earth nut then you could stick with the plastic enclosure pretty safely.

You want a lighting circuit and a supply for a consumer unit in the same cable

I hadn't checked the regs regarding this but its good to know its a no go!! I'll scrap that then.

You could install an small IP65 enclosure with DIN rail and fit a suitable MCB to protect the lighting circuit, but it might be easier to run an extra SWA for the lights.

You need an electrician to size up the job properly.
Also, this work is notifiable to your LABC under part P of the building regulations.

Is this cos I'm adding a circuit to the CU?
As there is no existing outdoor lighting circuit, I can't do anything then cos its all notifiable under part p.

Pretty much all work outdoors is notifiable bar a few things. Whether or not the outdoor lighting was a new circuit, this work would still be notifiable.

 

[Steve]

Though whether you notify is your business, and yours alone, unless the authorities or your home insurers find out.

 

[stevetogo]

Thanks for the advice guys,

I had no idea what a large job outdoor wiring was.

Tbh, I was trying to kill 2 birds with 1 stone by using the existing armoured cable to supply lights and an extra CU. The only reason being that it's already there!!
The idea of mounting an mcb in an enclosure seems like a good idea cos it means I could still use the cable for both purposes so it might be something I'll look in to but having read the comments on here I think I'll prob consult an electrician.

I am actually an electrical engineer myself but have NO experience of domestic installation & did the 17th edition over a year ago but as they say... use it or lose it and I rarely use it in my job so remember very little. I fully understand the need to do work properly and safely though so I might leave this to the pro's!

Even if I forget the extra CU for the time being and just concentrated on outdoor lights, is there anyway I can install these that doesn't require notifying the LABC?

 

[sparkwright]

POSSIBLY you could use a weatherproof fused spur for the outdoor lighting, instead of the junction box you were talking about.

Again, it's plastic so you would have to maintain armour earth continuity.

MK Masterseal range is best.

 

[LoveRocket]

Finally, what size MCB would this require and would it need to be RCD protected?

You have made no mention of the csa of the cable, the distance the cable runs (for volt drop calculations) or the proposed loading of the cable!

Volts drop has no bearing whatsoever with regards to the selection of the OPD.


All your other advice was sound though.

 

[bongos]

Volts drop has no bearing whatsoever with regards to the selection of the OPD.

Apologies. I thought it did.

I think this topic got discussed to death recently anyway.