Advice on Meter tails in flat

[markyj06]

Hi Just looking for some advice on meter tails in a flat.

The setup is 5 flats, i originally wired the meter tails in double insualted singles which was a mistake and am no in the process of rectifying it. Reasoning for calling it a mistake is the cable wont be rcd protected, for the majority of thier run they are in floor joists at a depth greater of 50mm but when they come up the wall to consumer unit they arn't. Reason for not rcd protecting is discrimination as if i put a 30ma RCD may be consumer unit that trips or Supply RCD which is in a service tunel. I could put a 100ma rcd but this wont comply as i understand as the cable are not buried at 50mm so either need mechanical protection or RCD. Hence i am now about to rewire in SWA. My question is i have already put in 16mm earth as well, so was planning on getting 2 core SWA and running this is to save wasting the 16mm earth. But just wanted to check i havent missed something i cant see why i cant leave the earth in place and use 2 core SWA for the supply?

Any replies would be great,

Thanks

Mark

 

[Rockingit]

Assuming that you'll be using 16mm SWA, a 2 core plus separate 16mm earth will cover all your bases.

 

[GLENNSPARK]

Assuming that you'll be using 16mm SWA, a 2 core plus separate 16mm earth will cover all your bases.

or just use a 3 core SWA....check prices....see which is the most cost + time efficient...

 

[markyj06]

Hi Thanks for the reply, yes it will be 16mm SWA as the isolators will be rated at 80amp and cutouts will be 80amp as well. In this situation my understanding is the seperate 16mm earth will provide the main earth and that the SWA is only earthed at the supply end and not terminated at the consumer unit?

 

[GLENNSPARK]

whats each flat geting (A)?

a 10mm G/Y may be enough...

 

[markyj06]

3 core swa is £1.20 a meter more exspensive and as i made the mistake of using singles i already have a 16mm single earth in place that is around 15 meter long so dont really want to have to pull it out if i can use it?

 

[markyj06]

Each flat is around 60amp demand

 

[craigyp2009]

I am in a similar dilemma, I have just been to a job to scope it out, and when I went there, there was no conventional "Fuse type" incomer, it was just coming from the ground to a standard 100A isolator, then the meter which seems a bit suspect to me, the house is reasonably new but definately over 20 yrs old and I cant remmember seeing anything amongst the IET updates saying that it was permissable for the distribution network to miss out the fuse type incomer and go straight to an isolator, I am a bit concerned about the fault protection.

I know that the 100A isolator would provide sufficient isolation, but my thought has alway's been that the incomer fuse is your last port of call for fault protection, so my main question is....

Has the law's governing the electricity distribution network operator's changed or has some fly by night been in and I need to get the distribution network operator's on-board and possibly cost my potential customer a fortune?

 

[Rockingit]

Leave the existing 16mm G/Y in place and just run the new SWA. There's nothing wrong with being too big in this sense.

 

[markyj06]

so the 16mm G/y doesnt need mechanical protection etc in any way as it will only carry fault current?

 

[craigyp2009]

in reply to your dilemma mate I would say that overkill is always a good thing as, when the iso's / rcd's etc are the weakest point's and the wiring is rated over the requirement then you are covered totally, me personally I allway's level with the customer and suggest better cable from the start to allow for future expansion, so, i.e. a customer requires a shower which need's 6mm cable I will suggest putting either 8 or 10 in so that in a couple of year's time when that shower goes pear shaped, they can get a bigger rated shower in without needing to re-do the entire cable run and need plasterer's etc etc etc

 

[Rockingit]

so the 16mm G/y doesnt need mechanical protection etc in any way as it will only carry fault current?

Correct. Well, I mean you should give it the normal love and gentle caresses that any cable deserves, and it needs to be installed suitably etc etc, but you don't need to give it protection as basically if someone damages it and comes into contact with the copper inside it's not going to be of danger to them.

 

[GLENNSPARK]

Correct. Well, I mean you should give it the normal love and gentle caresses that any cable deserves, and it needs to be installed suitably etc etc, but you don't need to give it protection as basically if someone damages it and comes into contact with the copper inside it's not going to be of danger to them.

might have something to do with it being considered not normally live...

only under fault conditions...and then only for the duration of the fault...

 

[bigspark17]

SWA is only earthed at the supply end and not terminated at the consumer unit.....

Not terminated at the supply end? How are you going to terminate the swa loose and dangling in the void behind fuseboard??

 

[GLENNSPARK]

anyway...
crap like this should be in the diy section...

 

[craigyp2009]

my personal thought is that if everything else is bulletproof and the protection point (mcb etc) is the only weak spot then you only have 2 places to look, the mcb / cu and or the faulty appliance, but either way your safe as houses, provided you rate correctly for each circuit and use your noggin lol

 

[craigyp2009]

my 2 main rule's are bullet proof everything and fault proof the lot, maybe it's a trait I have picked up from my dad but it has worked well for me so far, so if you need 4mm install 6mm and so on and so forth so you know NONE of your install can fall over

 

[markyj06]

When I said terminated I meant in the sense of the earthing of the steel armour, so I would connect the armouring to earth at the supply end and not at the consumer end.

- - - Updated - - -

Cheers glenspark helpful

 

[kingeri]

in reply to your dilemma mate I would say that overkill is always a good thing as, when the iso's / rcd's etc are the weakest point's and the wiring is rated over the requirement then you are covered totally, me personally I allway's level with the customer and suggest better cable from the start to allow for future expansion, so, i.e. a customer requires a shower which need's 6mm cable I will suggest putting either 8 or 10 in so that in a couple of year's time when that shower goes pear shaped, they can get a bigger rated shower in without needing to re-do the entire cable run and need plasterer's etc etc etc

Yeah, I use 8 loads myself, it's so easy to get hold of after all.

 

[Rockingit]

my 2 main rule's are bullet proof everything and fault proof the lot, maybe it's a trait I have picked up from my dad but it has worked well for me so far, so if you need 4mm install 6mm and so on and so forth so you know NONE of your install can fall over

It can also be a hallmark of poor design, though. Copper is an expensive precious mineral, and the world only has so much of it to dig out of the ground. Yes, there are times when you might consider putting in a 10mm instead of a 6 for a shower......but why install a 10kw+ shower in the future when they make naff all difference to an 8kw anyway? Why use 1.5mm for a lighting circuit when 1mm is already 140% over engineered for a 6A CPD..... and so on.

 

[markyj06]

Thanks for the help rockingit

 

[Rockingit]

Thanks for the help rockingit

You're welcome, it's what the forum is for.

 

[Flanders]

Hi Just looking for some advice on meter tails in a flat.

The setup is 5 flats, i originally wired the meter tails in double insualted singles which was a mistake and am no in the process of rectifying it. Reasoning for calling it a mistake is the cable wont be rcd protected, for the majority of thier run they are in floor joists at a depth greater of 50mm but when they come up the wall to consumer unit they arn't. Reason for not rcd protecting is discrimination as if i put a 30ma RCD may be consumer unit that trips or Supply RCD which is in a service tunel. I could put a 100ma rcd but this wont comply as i understand as the cable are not buried at 50mm so either need mechanical protection or RCD. Hence i am now about to rewire in SWA. My question is i have already put in 16mm earth as well, so was planning on getting 2 core SWA and running this is to save wasting the 16mm earth. But just wanted to check i havent missed something i cant see why i cant leave the earth in place and use 2 core SWA for the supply?

Any replies would be great,

Thanks

Mark

Just for you information you can not normally run double insulated tails over long runs anyway even if they are RCD protected the DNO wont allow it, But good on you for admitting your mistake and sorting it out

 

[Risteard]

Yeah, I use 8 loads myself, it's so easy to get hold of after all.

Beat me to it

 

[Paulgwat]

Hi Just looking for some advice on meter tails in a flat.

Reason for not rcd protecting is discrimination as if i put a 30ma RCD may be consumer unit that trips or Supply RCD which is in a service tunel. I could put a 100ma rcd but this wont comply as i understand as the cable are not buried at 50mm so either need mechanical protection or RCD.

I may have missed something here but wouldn't you need to discriminate in terms of time and not current? i.e. both upstream and downstream RCD's are 30ma but one is 30ms and the other 100ms.

That would minimise the likelihood of nuisance tripping of the upstream device should something happen in a flat but would also offer compliant protection of the cables without needing to go to SWA.

Again apologies if i have missed something obvious here, would be interested to know if this approach doesn't work as this is what was implemented and signed off for two remote distribution boards in my house / outbuildings

Cheers

Paul

 

[UKMeterman]

Hi,
It could be the case there has been someone messing, there should be a fuse somewhere. I do know of a few flats where there is a remote ryefield box. In this instance give the DNO a call.