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Message started by londonman on Oct 9th, 2016, 7:32am

Title: Lifetime of red/black cables?
Post by londonman on Oct 9th, 2016, 7:32am

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


Title: Re: Lifetime of red/black cables?
Post by Lectrician on Oct 9th, 2016, 8:15am

My house is 78.  I would not dream of rewiring or being concerned!

An upgrade to bonding and consumer unit would be the main thing, and checking for DIY bodges.

Title: Re: Lifetime of red/black cables?
Post by londonman on Oct 9th, 2016, 11:36am


Lectrician wrote on Oct 9th, 2016, 8:15am:
My house is 78.  I would not dream of rewiring or being concerned!

An upgrade to bonding and consumer unit would be the main thing, and checking for DIY bodges.


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  ;D

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Oct 9th, 2016, 2:55pm

If there is no RCD protection, I would say upgrade to a 17th AMD3 CU.

Protective bonding to gas/water services where they enter the building, within 600mm of stop tap/gas meter.  10mm earth cable.  At that age, you may not have any bonding, it may solid strand 2.5 or possibly stranded 6mm.

Title: Re: Lifetime of red/black cables?
Post by londonman on Oct 10th, 2016, 1:28pm

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.

Title: Re: Lifetime of red/black cables?
Post by londonman on Oct 24th, 2016, 7:26am

Lec, sounds like you have hit the nail on the head.  This is an extract from the surveyors report..

The incoming main appears not to contain an earth back to the grid; it is recommended that the incoming cable is altered to include an earth, so the electrical system can be earth-bonded and fitted with modern circuit-breakers for safety.

The incoming main passes an old main distribution box, with pull-fuses. It is recommended that the fuse boxes are upgraded to RCD boards. Ring mains and local wiring are in modern plastic-sheathed cabling .


No incoming earth?  Is that the responsibility of the electric company (the property is on the Northumberland/Cumbrian border.

What sort of price would one be talking about to have the consumer unit replaced?  Presumably if wires are too short to reach the MCB's inside it then extra lengths are crimped on ?  Just hope no 'borrowed neutrals' !

Do you know anyone up in that neck of the woods ?

TIA

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Oct 24th, 2016, 8:44pm

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.

Title: Re: Lifetime of red/black cables?
Post by londonman on Oct 27th, 2016, 10:11am


Lectrician wrote on Oct 24th, 2016, 8:44pm:
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.


Northumberland/Cumbria border



I know...no meter in shot.  Don't know where that is but going up in a couple of weeks so I can look then.

If you can recommend any electricians near Brampton ??

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Oct 28th, 2016, 7:22pm

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.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 11th, 2016, 7:37am

Now here's an interesting thing.  The electricity meter is locate 0.26 miles away (yes, a quarter of a mile away) at a farm. I haven't seen it but can only assume that the company fuse is also there.

This property was totally renovated 'within the family' back in 1979 and the location of the meter is that of a relative.  I have a nagging feeling that the main incoming cable was done 'on the quiet' and so God knows what's going to happen when I get a proper electrician along to replace the CU.

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 11th, 2016, 2:52pm

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?

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 11th, 2016, 3:19pm

Many thanks for the timely reply.  That's a good idea of yours.

Presumably the earth will be via the cable sheath ?

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 11th, 2016, 4:34pm

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.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 11th, 2016, 4:54pm

No worries. I've got a couple of calls out for a quote to do an EICR and replace the CU.

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 11th, 2016, 4:58pm

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.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 11th, 2016, 8:59pm

Will do. Many thanks.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 13th, 2016, 12:24pm

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

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 13th, 2016, 5:48pm

420 metre.  I would say 60 to 80amp load, you would be looking around 95mm to satisfy the voltage drop requirements!  Without calculating anyway.  Yours looks to be a 16 or 25.

Would be interesting to know the actual length, and readings.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 13th, 2016, 7:12pm

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 ?

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 13th, 2016, 7:59pm

Really depends on the figures.  Funnily enough, at a caravan park recently, I calculated the disconnection time to be 45 seconds or so for one of the circuits!  An RCD at the origin sorts it ;-)  300mA or even 500mA, time delayed.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 14th, 2016, 5:36am

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. :(

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 14th, 2016, 11:55am

Electrician going in tomorrow.

Talking to the vendor, apparently they tweaked the voltage to arrive at the house to be 260v !!  So when I fire up my Sedgwick MB planer with a massive inrush current .......

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 14th, 2016, 5:49pm

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?

 

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 14th, 2016, 10:17pm

I think we might be talking 'cowboy country'.  This was done in 1979.  There are only three properties at the end of the 11kv line.  

All the properties belonged to the same family, I believe.  Yes, the meter must be separate otherwise who would the householder be paying the bill to ?

There could be two transformers, of course...one tweaked.  WE shall see tomorrow.  Intriguing, eh ?

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 15th, 2016, 4:06pm

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  ;D

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.

Title: Re: Lifetime of red/black cables?
Post by Lectrician on Nov 15th, 2016, 9:28pm

How did you determine the length of run?  Measurement?  Are they doing a proper report for you?  A copy of that would be good.

135mm² isn't a size, it would be 120mm² or 150mm².  On that length of run, a DNO supply would likely work out cheaper!

If your meter and switch fuse is in a building elsewhere, you obviously need to make sure rights of access etc exist when the property is split off and sold.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 15th, 2016, 9:43pm

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.

Title: Re: Lifetime of red/black cables?
Post by londonman on Nov 16th, 2016, 4:40pm

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