Looking at buying a house that was totally renovated in 1979 and so will be red/black.  Is there a lifetime for these cables (leaving aside things like lying on top of polystyrene (IIRC...that leaches out/in to the insulation or something similar).

How does it degrade ?  What should I be looking out for ?

TIA

Lectrician wrote on Oct 9^th, 2016, 8:15am:


Thanks for the quick reply.  Can you expand a little re 'upgrade to bonding'?  Re the consumer unit....are you saying replace with a 17th gen one?  What happens if the cables are too short to easily do this ?

I can check DIY bodges just fine  

Thanks for the clarification, Lec.

No gas pipes.  Water pipes are plastic.  No idea what sort of mains connection. Out in the sticks.  Underground IIRC.

The earth may already be present, but not connected.  It may be a TT system, which would be fine if a rod existed and main RCD.

Photos of any of the incoming bits?

A CU upgrade would typically cost in the region of £300-£500, but really depends on area, how many circuits, etc etc.

That consumer unit is crying out for replacement.  The wiring doesn't look too bad.

The armoured cable feeding the consumer unit likely supplies an earth, but you would need to confirm at the sourcing end.

It doesn't look too big that cable.  On that distance, I would expect a far larger cable.

Volt drop will most likely be exceeded when you draw larger loads, and the earth fault loop impedance may well be exceeded too, depending on what protection is up at the origin.

A good test for volt drop would be to turn some lights on, and then switch a decent load on/off, such as a heater, immersion, cooker etc.  If you notice a substantial drop in brightness, you have volt drop issues.

Earth fault loop impedance can only be checked with a meter, but if voltage is an issue, earth fault loop is bound to be.

If the earth fault loop is exceeded, it means that a fault inside the consumer unit or on the cable up to it, may not clear within the 5 second disconnection time.  It could take far longer to cause the fuse/trip to operate.

Have you considered getting an Electrical Installation Condition Report carried out?

It could be the sheath, or the sheath and an integral conductor.  It's difficult to judge the size of that SWA, as it could be a 2 core or 3 core.

Would be interesting to see the report, and can happily interpret it for you.  Feel free to email any report you get if you're not happy posting it here in the open.

Ideally, what size cable would you like to see between the meter and the property ?

have to confess that I am now rather worried.  Presumably if the cable developed a fault - say someone shoved a pick-axe through it - then under normal circumstances the fuse would blow, the damaged part repaired, the fuse replaced.

But if the fuse doesn't blow in the timeframe required then the cable could overheat and need replacing ? Or am I worrying unnecessarily on that score seeing as how it is buried in the ground.  The fuse might not blow within five seconds but may be ten seconds ?

Is that a solution LEC ?  A time-delayed RCD ? That would sort out the protection issue then?

Then all that one would be left with are the volts drop and possibly explains why they use Calor gas to cook.

Trenching costs alone look to be £15k.

It's unusual for them to be able to tweak voltage - Only the DNO can alter tappings on the transformer, and while they could, it would mean the voltage at the origin would be higher than permitted.

I wonder if the supply at the origin is shared with others?  Do you have your own meter for this property?  A meter belonging to a utility company?

Duff gen by the current owner or maybe he was being disingenuous. The voltage is 240v.

Cable size is 35mm about as far as they can judge.  It's not 440m...more like 800m as my measurement was as the crow flew.

They calculate a 60v drop at 60A load (the size of the cut-out).  So a 10KW electric shower is out of the question  

Cable size needed probably 135mm.  Or a service alteration.  I think the latter.

There is no earth or if there is it is reliant on the sheath which is not 10mm in equivalence.  No earthing of any of the internal copper water pipes.

I determined the length of the run simply using the dimension tool on the Magic site (brilliant site, by the way).  They walked the route ad subsequent to their visit I now have the plan showing the route of the cable.  

Re 135mm..to be fair to him he did say that it was finger in the air.

Yup, definitely a Service Alteration is on the cards.  I am asking him to fill in the form on my behalf..much easier what with him being up there etc.  Have to say that I think he's OK.  Glad I got in contact with him.

Your point re access etc is a good one but not applicable in this instance.

One other good reason for an SA is that imagine fitting an RCD up at the meter to sort out the earth loop issue ?   Intermittent cable fault.  Trudge up in the wet and snow to reset the RCD.  Trudge all the way back.  Few minutes later, it trips again...repeat.

Much better to have my own wee transformer on a pole and the meter in my house (just as long as it's not a smart meter!  That'll be another interesting conversation))

Mind you, there's no mobile signal and so the smart meter will be stuffed anyway.