Terminating armoured cable

[Peter Watson]

Hi all,

I'm intending to run a power feed out to the garage soon. The route will be straight through the wall from the under stairs cupboard to the outside, up the wall approx six feet and then horizontally to the corner of the house. From there it will go along the top of a short fence/gate (about 10 feet) and through the garage wall.

The plan is to run a 4mm armoured cable for this, fed from a 32A MCB and terminating it in a small CU in the garage. I did look at Hituf but it's about twice the price... The plan is to move the freezer to the garage so the garage CU will have a 16A MCB for that, a 6A MCB for lighting and a 16A RCD for general power.

Two questions:

1. Is this arrangement allowed? A google search brought up some post earlier this year about outbuildings being fed TT and not using the house earth. This scuppers the freezer plan!

1. How do I make off the ends of the armoured cable? The house CU is plastic so obviously I need to run some 4mm T&E from there into a metal box and join it to the armoured cable. Are the gland kits fairly self explanatory in their use or are them some pointers on how to do it?

Thanks for any info,

Peter

[Christian McArdle]

In the garage, you say you will use a 16A RCD. This doesn't make sense. An RCD has only earth leakage protection, but no overcurrent or short circuit. I would use a B20A/0.03 RCBO for this purpose. This protects against all three.

Earthing is something that needs to be considered. If you decide to export your house earth, you'll need to run main equipotential bonding to the garage if it has any structural metalwork or metallic services. This could be very difficult to achieve. It is much easier if there is no such services or metalwork.

The alternative is to install a TT system in the garage. This would consist of an earth rod and a consumer unit with a 100mA Type S RCD incomer, a B16A MCB for the freezer, a B6A MCB for lighting and the B20A/0.03 RCBO for the general power. The RCBO is guaranteed to discriminate with the 100mA Type S for earth leakage on the general power circuit. Although there are a number of points of failure that could take out the freezer, the most likely is eliminated (earth leakage on the socket circuit). It doesn't take much work (or equipment) to install, although the earth rod would need to be tested, and you would need an extra residual current device (which might cost a little bit).

Run PVC T+E in the house. Only go into armoured cable where you go through the external wall. You should find instructions for installing the glands in the packaging. Otherwise, a bit of googling (and a hacksaw) may help.

Christian.

[Peter Watson]

Lazy typing on my part! I'll either fit an RCBO or a cheap split CU depending on which is cheaper..

There are no services in the garage fortunately so I assume it is permissible to use the sheath of the cable as the earth in this instance?

I'll continue googling then :) Having never worked with the stuff before I want to make sure I get it right... Of course it may be easier/cheaper to run 4mm T&E all the way, protected by conduit on the external run?

Thanks for the reply,

Peter

[Christian McArdle]

Cheap split may be marginally cheaper, but RCBOs look more better! (and take

1 or 2 less ways in the consumer unit!).

And no structural metalwork? However, if you don't go TT, you really do need to test the earth loop impedence properly using an earth loop impedence tester (costs lots to buy). I'd be tempted to go RCBO on the other circuits too, to be sure. Belt and braces.

I wouldn't use T&E for this. Definitely use SWA.

Christian.

[Andrew Gabriel]

You can hire them. I hired one a couple of years ago over a weekend, and there were several of us at work who used it over that period (I think it was about 6 houses checked) and shared the cost. It would be expensive to hire it to check just one house.

[Chris Oates]

Nope

[JimM]

A quick tip when connecting up the glands is that there is a small brass ring as part of the connection. This ring is tapered and will only go on one way - I spent 2 bloody hours trying to get the bastard thing to do up before someone pointed this out to me :)

Other than that I found the job pretty straight forward with lots of advice to be found on this group

Jim

[<nightjar>]

You may find it doesn't work so well there. Most freezers are designed to work in the ambient temperature of the average kitchen.

....

For my garage, I ran T&E through conduit into to an external IP68 junction box and took the armoured cable from there. The box does not need to be metal. The terminations come with an earthing tag, so just connect that to earth at one end of the cable.

The last ones I bought came with instructions, but I've always found them fairly straightforward.

Colin Bignell

[Peter Watson]

So, other than an earth rod, how does one provide an earth using SWA?

Peter

[Peter Watson]

Yes I remember that discussion a while back.. My freezer is on it's last legs so if there's a problem I'll replace it with one that will run outside.

So the sheath is only a protective earth.. I'm really not keen on the earth rod approach so I might have to rethink this! Peter

[Andy Hall]

The gland assemblies, which are normally brass, usually come with an earth tag which goes onto the barrel and is held in place with the nut. An earth wire is attached to that and run to an appropriate earth terminal.

.andy

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[Sean Delere]

Hope this helps