banquo

A colleague has an underground cable running as a spur from the downstairs ring main. It's been there a long time, and is thought to be PVC running in conduit. It's failed with an earth fault, so has to be replaced.
He's had a quote for digging up the garden, and replacing the cable, but that's not only expensive, but it going to wreck the garden.

An overhead line would be possible, but is a non-preferred option, as it's a longish run of 25 metres or so, and, due to a steep slope, the garage is actually higher than the top of the house.

I'm wondering if it's permitted to run armoured cable above ground along a perimeter wall, to avoid all that excavation and damage. We have plenty of external armour runs in industry, unprotected, but is it allowed in a domestic setting?

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Docara

Of course it is - SWA Steel Wire Armoured

I'm assuming he has a socket in the garage - The best option would be to stick it in the consumer unit on it's own RCD (or RCBO) put a local Consumer unit in the garage 2 or 4 way (depending on Size) and install an Earth rod. Effectively converting his supply to a TT in the garage

The benefit is you can run lightys, extra sockets from the location rather than the house.

Note make sure you consider all possibilities of loads before buying choosing the cable size - Before doing the calcs I would assume a minimum for one double socket and light to be 4mm

Docara

banquo

Thanks for that mate. So, it's OK for the cable to be clipped up above ground along the garden wall? I think the most recent plan is to take a 4mm 3core armour, run in a trench from house to wall, 450mm down, with tracer tape, come up when it reaches the wall, clip up along the 25 yeard length of wall, then trench againto enter the garage from below.

__________________
Before all else, be safe!
^^^^^^^^^^^^^^^^^^^^^

Docara

Yes! Yes! Yes!

NO NEED TO DIG A TRENCH!

The armour in an armoured cable is for mechanical protection. Apart from asthetics (spelling??) fixing it to a wall is by far the best (quickest) option.

[url=http://www.doncastercables.com/cableCalculator.asp[/URL]

Follow the above link I used 30m of cable, 16A at 5% Volt drop = 2.5mm cable
Now I would see the difference in price between 2.5 and 4mm and if the difference is small go for 4mm every time.

I have a concern you are not addressing the earthing options/issues here - are you a sparks

banquo

Not me; electrical design engineer... Theory OK; practice, less so...
AFAIK the existing set-up comes from a 25A RCD, earth from the consumer unit. They are effectively replacing what's already there. The armour will be 3-core, live, neutral and earth, with the armour earthed through the gland to steel boxes each end. If, as you say, it's OK to take it along the wall, I'll suggest he gets a sparks in to do it. Will be a load cheaper without all that digging////
Appreciate your help.

__________________
Before all else, be safe!
^^^^^^^^^^^^^^^^^^^^^

Docara

Howdy

Why don't you clip it along the wall - cheaper still!!!! Just let the sparks do the final cutting to length and connection make sure he issues a cert.
From the link I gave you get the 2.5 cable, cleets (to suit), garage consumer unit and save yourself a bit more.

From memory I'm guessing for 2.5mm2 the spacing is 600mm (2 hammer lengths to neck) but see what looks the best and doesn't allow the cable to sag - obviously.

Cheers
Matt

banquo

All sorted. Thanks for your help!

__________________
Before all else, be safe!
^^^^^^^^^^^^^^^^^^^^^