What Size...

[wreck-it-steve]

Hi,

Quick question about my meter tails... I have a 100a service head with an 80a fuse in, from there we have 16mm tails and 16mm earth. From the meter to the consumer unit there is 16mm tails and 16mm earth. We have no electric shower (comes from heating) and our cooker is only rated at 13a. Will this be OK or does it require looking at to be changed?

I'm not sure of our earthing arrangement but when British gas came to change our meter I got a look in the service head while he was checking it and there looks to be a split con cable with bare copper going in to the neutral and separate bare copper going to the earth block in the service head (the bit where you would PME it from)

Just a bit of advice please

THanks

 

[GaryMo]

16mm² tails are fine with a 80A supply and probably a low maximum demand.

Your earthing arrangements sound like TN-S.

 

[Lectrician]

16/16 with an 80amp service head is absolutely fine, and the norm around here (100amp services here use larger heads).

The neutral would not be 'bare' if split concentric:

 

[westie101]

With respect what has the size of the cut-out and the main fuse got to do with it?

Surely it is the size of the incoming cable that is the critical factor.
Even a 16mm2 concentric is rated at over 100A on a DNO system so the fuse could be uprated!

(I agree TN-S with a concentric cable)

 

[wreck-it-steve]

16/16 with an 80amp service head is absolutely fine, and the norm around here (100amp services here use larger heads).

The neutral would not be 'bare' if split concentric:

Its like the first picture.

 

[wreck-it-steve]

With respect what has the size of the cut-out and the main fuse got to do with it?

Surely it is the size of the incoming cable that is the critical factor.
Even a 16mm2 concentric is rated at over 100A on a DNO system so the fuse could be uprated!

(I agree TN-S with a concentric cable)

I only have a 6 way consumer unit (all RCBO's) and there is no room for anything bigger where it is so in order for more demand someone would have to get an electrician in to alter it all anyway and then I would assume they would upgrade the tails then. Im assuming its a split con cable, it looks like the first picture above although i think its about 10-15 years since it was done.

 

[GaryMo]

The 16mm² tails (and 80A supply fuse) wouldn't need upgrading even if the consumer unit was changed, a 10kW shower installed and a 6kW double oven. There's plenty of similar installations up and down the country that run without problem due to the nature of the loadings. Not all appliances are on at the same time, ovens are constantly switching on and off via thermostats etc.

 

[EFLImpudence]

Even a 16mm2 concentric is rated at over 100A on a DNO system so the fuse could be uprated!

Question not directed specifically at Westie.

As that is the case, why are 'our' 16mm² singles rated at only 87A?


Edit -
nominal csa of 80A fuse-wire - 2.54mm²
nominal csa of 100A fuse-wire - 3.14mm²

 

[westie101]

Bear in mind that the cut-out fuse is NOT there to protect from overload, in fact with a fusing factor of 1.47 it will carry 120A for quite an extended period.

 

[RF Lighting]

Even a 16mm2 concentric is rated at over 100A on a DNO system so the fuse could be uprated!

Question not directed specifically at Westie.

As that is the case, why are 'our' 16mm² singles rated at only 87A?

Because our equipment is designed with a maximum operating temperature of 70°C and IIRC the DNOs is 90°C

Also a lot of new DNO cabling is aluminium which might make a difference?

 

[EFLImpudence]

Because our equipment is designed with a maximum operating temperature of 70°C and IIRC the DNOs is 90°C

Ah. that could be it. Thanks.

Also a lot of new DNO cabling is aluminium which might make a difference?

That would reduce the ccc for the same csa.

 

[westie101]

That would reduce the ccc for the same csa.

We use a larger csa to maintain the ccc I.E. 35MM2 AL is the equivalent of 25mm2 Cu. In reality the use of XLPE has had an effect as it is a poorer heat transfer medium than other insulators.

 

[EFLImpudence]

Yes, I realise that but my question was in relation to this thread with 'your' cable of 16mm² split concentric (ccc over 100A
(105 ?)) feeding 'our' single tails of 16mm² (ccc 'only' 87A) obviously carrying the same current at any time.

The higher allowed temperature would answer queries about why we have to fit larger tails when the supply is smaller yet still acceptable.