We are bound by a completely different set of standards and laws. We also use different ratings for cables than the IEE regs using 8 and 3 hour ratings.
(though the one I work for does not use that type of cable.)
Incoming meter wiring under-rated?
- Thread starter Kaymo
- Start date
We are bound by a completely different set of standards and laws. We also use different ratings for cables than the IEE regs using 8 and 3 hour ratings.
(though the one I work for does not use that type of cable.)
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[/quote]
We are bound by a completely different set of standards and laws. We also use different ratings for cables than the IEE regs using 8 and 3 hour ratings.
(though the one I work for does not use that type of cable.)[/quote]
Would your standards normally allow a 10mm² cable to carry a 100 Amp single phase supply inside a building?
We are bound by a completely different set of standards and laws. We also use different ratings for cables than the IEE regs using 8 and 3 hour ratings.
(though the one I work for does not use that type of cable.)[/quote]
Would your standards normally allow a 10mm² cable to carry a 100 Amp single phase supply inside a building?
As I pointed out, my DNO doesn't use it so we don't have a rating for it.
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Fair enough, but what could be a bit difficult to get one's head around would be a situation in which the same DNO which fed a household with 10mm² cable expected to see 25mm ² meter tails leaving their meter - although, I obviously I don't know if that would be the case with your DNO.
Kind Regards, John.
Hmm it depends on who you ask that one, as I recall the requirement is to match the copper equivalent size of the incoming supply cable with the earth being 50% of that size.
It is usually assumed that the incoming cable is 25mm2 or equivalent so the 25mm2 tails are used.
In reality we have a huge number of 16mm2 cables in use and if I found anyone insisting on 25mm2 tails I would discuss it further.
Of course to cater for the lowest denominator some just specify the larger size as it is easier
It is usually assumed that the incoming cable is 25mm2 or equivalent so the 25mm2 tails are used.
In reality we have a huge number of 16mm2 cables in use and if I found anyone insisting on 25mm2 tails I would discuss it further.
Of course to cater for the lowest denominator some just specify the larger size as it is easier
Even 16mm² tails are unnecessarily large when combined in series with a 5m+ run of 10mm² sitting on top of loft insulation
That would sound like common sense - but, with the 10mm² supply we've been talking about, that would very probably make the tails non-compliant with the consumer-side regulations (i.e. BS7671)
Again, that makes sense, but I have heard of a good few cases in which it was being said that 16mm² tails were inadequate/unacceptable, despite the supply being 16mm².
Yes, I strongly suspect that is what was happening in the sort of cases I'm talking about - on the basis that it's easier to always specify the larger size than to think!
Kind Regards, John.
I don't disagree, nor do I agree that the cable that supplies your property is acceptable. Unfortunately I am in an different DNO so can't influence matters. I would hope that a bit of discussion with whoever comes to sort the earthing might end up with a replacement service cable.
Ahead of the guy coming out tomorrow I did another earth loop test tonight, this time directly on to the earth coming into the property rather than the sockets and got >500 Ω. The approx 50Ω impedance I am getting at the sockets is obviously coming from a connection somewhere to a water pipe and there is no incoming earth at all - so perhaps they might have to replace the cable after all.
SP have a duty to respond to a poor earth within a specific time
Tell them you have a tn-s supply and your earth reading is what you state
It's their earth and their supply cable so it's thier duty to maintain it
They record their calls so you can request a copy of the conversation where they state the supply is OK
Insist they give you a job reference number and call them on 0845 2727999
Since these utilties went to a private company they will do anything to stall coming out and try to make a job chargable
Insist they get someone out to check the earth (with parallell paths missing) and look at his meter when he is testing
let us know how you get on
Tell them you have a tn-s supply and your earth reading is what you state
It's their earth and their supply cable so it's thier duty to maintain it
They record their calls so you can request a copy of the conversation where they state the supply is OK
Insist they give you a job reference number and call them on 0845 2727999
Since these utilties went to a private company they will do anything to stall coming out and try to make a job chargable
Insist they get someone out to check the earth (with parallell paths missing) and look at his meter when he is testing
let us know how you get on
Very good point.
I reported a high Ze on a TN-S supply.
Chap from the DNO came out, and did a loop test with the parallell paths in place, and told me the supply was fine. I removed them and got him to test again.
They converted the supply to TN-C-S with a bonded lead sheath on the supply cable.
The saga continues...
Guy from SP came out yesterday, he didnt even need to check the impedance as the first thing he did was follow the line back to the pole and the earth wire is not connected at the pole, just tied back. He said that SP had never supplied an earth and so were not obliged to rectify this. If I wanted to request an earth from them it would likely be very expensive and probably would be cheaper for me to resolve things at my end.
In fairness to him he was a decent guy and spent a bit of time going through things. He advised that as the earth was less than 200Ω I could make the installation safe by getting an RCD fitted post meter/pre consumer unit, or just replacing the consumer unit with an RCD protected consumer unit, and by doing this the 50Ω would be adequate.
On a positive note he did see my point about the incoming cable and he has recommended that it be replaced.
Guy from SP came out yesterday, he didnt even need to check the impedance as the first thing he did was follow the line back to the pole and the earth wire is not connected at the pole, just tied back. He said that SP had never supplied an earth and so were not obliged to rectify this. If I wanted to request an earth from them it would likely be very expensive and probably would be cheaper for me to resolve things at my end.
In fairness to him he was a decent guy and spent a bit of time going through things. He advised that as the earth was less than 200Ω I could make the installation safe by getting an RCD fitted post meter/pre consumer unit, or just replacing the consumer unit with an RCD protected consumer unit, and by doing this the 50Ω would be adequate.
On a positive note he did see my point about the incoming cable and he has recommended that it be replaced.
Whilst it is literally true that either of those approaches would make the installation safer as a temporary measure, I can't see it as acceptable, 'safe' or compliant with regulations as a long-term solution.
If I understand correctly what you're now saying, you do not have either an earth from the elcetricity supplier or an 'earth rod', so the connection to earth you're seeing (50Ω or whatever) presumably must be the consequence of (deliberate or otherwise) 'bonding' to incoming water and/or gas supply pipes. Reliance on such an earth is not permitted by regs (I think it ws in the distant past), not the least because the utility supplier(s) might one day replace virtually all of the underground supply pipe with plastic. In effect, you have an installation with no guaranteed reliable earth connection.
If the electricity suppliers are not going to provide an earth, it would seem that your only definitive long-term option, and the only one compliant with the regs, would be to get an earth electrode ('rod') and turn it into a 'TT' installation.
That's how I see it, anyway.
Kind Regards, John.
edit: typo corrected
Thanks for your comments John. You are correct, there is no earth from the supplier, and as far as I am aware there is no earth spike. There is no gas in the house so the only earth must be from the water pipe, which I confirmed with a near zero resistance between a socket earth and a nearby radiator pipe.
From the point of view of the regs, do these regs apply to existing installations or only new installations? There must be many older houses like mine where the only earth connection is through the water pipes.
From the 'safe' point of view I am not sure I understand why a 50Ω Earth would not be sufficient. In the event of a short between live and earth the RCD would trip, in the event of a person being the earth the RCD would also trip?
From the point of view of the regs, do these regs apply to existing installations or only new installations? There must be many older houses like mine where the only earth connection is through the water pipes.
From the 'safe' point of view I am not sure I understand why a 50Ω Earth would not be sufficient. In the event of a short between live and earth the RCD would trip, in the event of a person being the earth the RCD would also trip?
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