meter tails

[martinsayer81]

hi guys, i need your help (again)

when upgrading the meter tails to 25mm, how far back do you replace them?

what i mean is, do you replace the tails all the way back to the main cut out? i thought we weren't allowed to touch the electricity meter, or even the cut out??

would you take the old tails out of the c/u, and put them into a double pole isolator, then use 25mm tails from there to the c/u, then ring dno to upgrade the rest???

 

[Tonkatoy27]

ELECSA officially advise that whatever the domestic cut out fuse size, if there is no sign of damage or deterioration of the original 16mm tails then they can be re-used.

 

[rich.250]

It's as simple as CCC of tails and fuse rating.......

 

[Moses]

I think you're getting confused here with having to provide independent overcurrent protection to tails more than 3m long. An isolator won't provide this.

If tails are protected by 100A fuse at the head, then why do you have to provide an other 100A switch fuse after the meter, where is the discrimination?

All that is required is a means of Isolation in case that the long tails after the isolator are damaged/shorted somewhere in the property, to allow for emergency isolation only, not for overcurrent protection.

 

[Plonker 3]

All that is required is a means of Isolation in case that the long tails after the isolator are damaged shorted somewhere in the property, to allow for emergency isolation only, not for overcurrent protection.

Which in turn will blow the DNO fuse which they won't take too kindly too, which is why providing a KMF switch fuse will be required so anyone can replace the fuse.

 

[GaryM]

Moses, it is for overcurrent protection of the extra long tails as the distributors fuse isn't there for that reason.
You'll never achieve discrimination unless you're preparred to cripple an installation with a fuse size half that of the distributors so I'd just match it.

 

[Moses]

Which in turn will blow the DNO fuse which they won't take too kindly too, which is why providing a KMF switch fuse will be required so anyone can replace the fuse.

If tails are protected by 100A fuse at the head, then why do you have to provide an other 100A switch fuse after the meter, where is the discrimination?

Read more: http://www.electriciansforums.net/e...al-forum/59438-meter-tails.html#ixzz1z1Nnqb5u​

 

[Moses]

Moses, it is for overcurrent protection of the extra long tails as the distributors fuse isn't there for that reason.
You'll never achieve discrimination unless you're preparred to cripple an installation with a fuse size half that of the distributors so I'd just match it.

So even with a 100A fuse at the head and 100A fuse in the new switchfuse,

How do you ensure the the DNO fuse is kept intact in case of a fault?

 

[GaryM]

So even with a 100A fuse at the head and 100A fuse in the new switchfuse,

How do you ensure the the DNO fuse is kept intact in case of a fault?

You can't, unless you're willing to drop to a 50A fuse in the case of a 100A supply, 40A fuse in the case of an 80A supply....etc

 

[Plonker 3]

You can't guarantee that, but at least you are providing a OCPD before the DNO fuse so all relevant precautions are taken to stop there fuse blowing. There is no reg saying every fuse has to be lower than the last on in circuit.

 

[GaryM]

This is a reply from a guy that works for a DNO over on the IET forum relating a question about extra long tails without customers overcurrent protection:

"That would get a "danger notice" from me if I spotted it here. Within 3m cable distance of the electricity meter (or whatever figure the DNO use - we use 2.500m), there must be overcurrent protection. An isolator is not good enough. For a new-build, we would refuse to connect the supply."

 

[Moses]

This is a reply from a guy that works for a DNO over on the IET forum relating a question about extra long tails without customers overcurrent protection:

"That would get a "danger notice" from me if I spotted it here. Within 3m cable distance of the electricity meter (or whatever figure the DNO use - we use 2.500m), there must be overcurrent protection. An isolator is not good enough. For a new-build, we would refuse to connect the supply."

This is another opnion - not mine but from an electrical forum.

Moses dear, it isn't a requirement of BS7671 at all. Neither is it a Suppliers requirement to have a switched fuse for tails exceeding 3 Metres. But some suppliers insist on a 100A DP isolator for domestic services. In fact, the current trend for suppliers now, is to energise new-builds with a live meter and DP isolator even before the property has been first-fixed by the electrician. It never has been a requirement of any Regulatory Body or any non-statutory code, such as BS7671 for such a ridiculous situation as two 100 fuses in close proximity. There are too many old wives' tales in this industry..........​

 

[Orffyreus]

hi guys, i need your help (again)

when upgrading the meter tails to 25mm, how far back do you replace them?

what i mean is, do you replace the tails all the way back to the main cut out? i thought we weren't allowed to touch the electricity meter, or even the cut out??

would you take the old tails out of the c/u, and put them into a double pole isolator, then use 25mm tails from there to the c/u, then ring dno to upgrade the rest???

I am sure if you look again tomorrow you will see that the seals are missing and may just replace the tails with 25mm2

 

[sjm]

The NIC told me that tails over 3 mtrs require additional isolation not fusing. I was also told the same by a Western Power engineer, who had no idea about where the 3 meter requirement came from.

IMHO the confusion comes from reg 433.?.? which talks about the need to have overcurrnt protection for cables with a lower ccc than the circuit feeding them is rated at, to have that protection within 3 meters of the change in cable ccc.

 

[Moses]

The NIC told me that tails over 3 mtrs require additional isolation not fusing. I was also told the same by a Western Power engineer, who had no idea about where the 3 meter requirement came from.

IMHO the confusion comes from reg 433.?.? which talks about the need to have overcurrnt protection for cables with a lower ccc than the circuit feeding them is rated at, to have that protection within 3 meters of the change in cable ccc.

Thanks for that.

 

[HandySparks]

If tails are protected by 100A fuse at the head, then why do you have to provide an other 100A switch fuse after the meter, where is the discrimination?

All that is required is a means of Isolation in case that the long tails after the isolator are damaged/shorted somewhere in the property, to allow for emergency isolation only, not for overcurrent protection.

I didn't just make it up.
See section 8 of the document "De-Energisation - Frequently Asked Questions"
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