Help with old undergound supply cable

[AndyNewBuild]

Hi All,

Hopefully someone can advise on the best course of action regarding an old underground armoured cable.

I'm in the process of a knock down and rebuild. The old cottage has an underground armoured cable which comes from an overhead line in a neighbouring field. This was installed approximately 30 years ago towards the end of the 70s. The problem is that the supply cable running to the current meter appears to be very small and I'm concerned it won't be sufficient to feed a modern 5 bedroom house. The cable is approximately 6mm in diameter. The cable comes down the main pole, across a field, through our plot to the meter. However the cable coming down the pole is much thicker than that entering the meter. I assume that there must be a junction box somewhere on the border of our property where the two meet.

I have obtained the maps from Central Networks but this does not give any information about any junction boxes.

If I do need to replace this cable how do I go about finding the junction? I have already had a CAT scan for the cable and located where it runs but have been unable to find any junction.

Any advice greatly appreciated.

 

[securespark]

It's not your cable to replace, surely?

If it comes off a pole, it will be the responsibility of the DNO.

It's most probably not SWA either. It will probably be straight concentric feeding a PME head.

Did you really mean 6mm diameter?

 

[RF Lighting]

Did you really mean 6mm diameter?

Thats what he wrote

@OP, what is the rating of the cutout which this cable supplies?

What is the proposed load of the new property?

 

[AndyNewBuild]

Thanks for the quick reply.

I'm unsure if the cable coming through my site is my responsibility - that's one of the problems! I'm not sure who put the cable in but it was the first electricity supply the cottage had.

I have excavated around part of the underground cable beneath the current patio. I'll meaure the diameter tomorrow but you're correct I think it's overall diameter is probably about 15mm, not 6mm!

Can you explain what you mean by straight concentric to a PME head? If it's not SWA, does that mean it's vunerable to mechanical damage?

 

[AndyNewBuild]

Cutout is rated at 100AMPS.

I haven't had the total load calculated yet but the house will have a normal load distribution except for the fitting of a ground source heat pump which I understand has a large current draw.

 

[securespark]

See here for supply cable types:

//www.diynot.com/wiki/electric...bles_straight_concentric_and_split_concentric

 

[AndyNewBuild]

Thanks for the link. I wasn't aware of this type of supply cable. The cable has writing embossed on the outer sheath. I think it says 600/1000v but will double check.

Looks like I need to get an electrician to have a proper look before panicking that I need a new cable!

Thanks for the replies guys, much appreciated.

 

[securespark]

It's not really your worry, mate. If you have a 100A fuse in the cut-out, that should be sufficient.

If you want more, ie a 3p supply, you'd have to pay for it, and the DNO would have to do the work.

 

[JohnD]

does "normal" include electric heating?

Consider how many appliances you will have that use significant amounts of current (those with heating elements inside them - ovens, hob, washing machine, dishwasher, tumble drier, immersion heater, electric shower, sauna, swimming pool, hot-tub, patio heaters etc - lighting is not significant unless you like searchlights - and add up the kW or Amps at max load.

If you have a 15mm dia cable it is probably OK for 100A which is the most you normally get for a house. Depending on how close you are to your Pole Transformer you will get some voltage drop if you insist on using an electric hob or electric shower.

Electricity supply cables upstream of the consumer's meter are allowed to be loaded above the ratings you will see in the capacity tables as they are not bound by the same rules. Also a cable in the ground or open air can lose heat fairly easily.

The difference in apparent cable size might be where an old armoured cable was jointed to a more modern one. In which case there is probably a buried permanent encapsulated joint (epoxy resin or tarry stuff) and no junction box.

 

[ColJack]

are there 3 or 4 wires on the overhead lines?

is there any other properties nearby?

the cable coming down the pole might be a 3 phase supply that runs along the border of your property and any neighbouring properties and is "tapped off" like regular houses are..

they put a joint in and take the cables they need to each house.

 

[AndyNewBuild]

Thanks for the replies.

The overhead cables which the underground one is connected to has 3 overhead lines. The pole which has our transformer on it has the name of our property on it and only serves our property. We our in a rural location and have no near neighbours.

The cable connecting to our meter has C.A.P. Ltd on it along with 600/1000v.

Here's a few photos of the setup. Hopefully these will help someone identify the cable type and size.

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• AndyNewBuild
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• AndyNewBuild
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• AndyNewBuild
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• AndyNewBuild
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• AndyNewBuild
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[aptsys]

All looks fine for 100A, and yes that is split concentric cable. If your demand is more than that, you'll be needing a new transformer too, but this is all the DNO's concern (except the bill they'll be posting to you )