Jason Kelwick is worried about there being only 16mm meter tails from the cut out to the meter, and after the meter, at a dental surgery electrical installation. His question has been answered by the NICEIC (Theme – Distribution Equipment):
Question: I've recently been asked to install new sockets at a dental surgery, the building was previously a public house. It is fed by a single-phase TN-S supply.
Upon inspecting the mains, I noticed that the tails from the cut out to the meter, and after the meter, are only 16mm. After the meter 16mm tails feed a Henley block, then three separate sub-main cables (twin & earth) feed three distribution boards, all 16mm.
The main earth is 16mm, and the gas and water are bonded with 10mm - so there are no problems there.
The supplier's cut out appears to be quite new, it is marked BS1361, 100A. The fuse cut out is sealed so it is not possible to see what size fuse is fitted in the carrier.
My question is - what should an electrical contractor do about this?
As far as I can work out I have the following options:
Inform the occupier and tell he/she that they need to get in touch with their supplier to get the tails upgraded, This may be expensive - what if the occupier says 'no'?
Attach a sheet to the certificate stating that the sub-main cabling within the building is possibly under-rated for the main fuse fitted, and suggest a further investigation?
Telephone the supplier and ask whether I can remove the seals and pull the main fuse so that I can upgrade the meter tails myself?
Would it be acceptable to install a 63A switch fuse after the Henley block, so that the installation would then be effectively protected against any overcurrents?
Answer: We would like you to consider the following:
Inform the occupier - There is normally no charge made by the supplier for the first visit. They have a duty of care in accord with Electricity Safety, Quality and Continuity Regulations 2002 (SQCR 2002 for short). If you contact the occupier and clearly but simply outline your concerns, we have found most of them to be amicable.
Attach a sheet - This serves to notify everyone, but it does not address the problem.
Telephone the supplier - Mention that an upgrade is required to the installation and could they provide a disconnect / connect for you. Please note, however, that if this option is chosen, you will quite likely be asked to supply an EICR for the whole installation before they will energise the circuits.
Install an isolator - to do that you will still need to contact the supplier, as you should not be working in it live - this would prove to be the most expensive of all the choices.
See the Electricity at Work book HSG 85 pages 4 and 5, which elaborates further on this subject. As you will see, there are several options open to you.
Once you have carried out an assessment of the installation, it will quickly become obvious which route to take to rectify this problem.
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