Electrotechnical question

i am installing a shower in a new bathroom at home. it is rated at 9.5kw @ 240v and 8.7kw at 230v. as my electrical knowledge is well out of date and i am not due to renew my well expired 17th edition until the new year, i wondered if i may pick the brains of forum electricians with up to date knowledge (and understanding) of amendments 1, 2 & 3.

i have been trying to make head or tail of the latest regs. i understand that bonding all the metalwork in the bathroom is no longer necessary except in special circumstances??. the pipes are all copper (only plastic wastes) except the house incoming water which is lead. does the shower and switch need bonding still? it will be wired through a new amendment 3 compliant fuseboard (all metal with rcd's). i have pulled through a 6mm power cable through an uninsulated stud wall up to the loft where it will sit under the loft insulation for a length of about one metre. i read up on this but have wondered whether i should install 10mm power cable instead? if it needs bonding i presume it will need a 10mm earth bonding and i am undecided whether to take it back to the lead water pipe or the incoming gas?

our current 20 year old shower has no bonding but the bathroom and kitchen metalwork does have supplementary bonding. this bathroom will be ripped out. our existing consumer board is a vintage four way rewirable which has mcb's. this will be replaced with the new one.

any solid advice appreciated.

---------- Post added 15-12-2016 at 12:28 ----------

nobody up to date with current regs then?

The shower will be earthed through its supply cable.

Supplementary bonding can be omitted if your bathroom circuits have RCD protection and minimum disconnection times can be met, which the rcd will achieve, and the pipework is effectively connected to the MET. Measure the resistance between the bathroom pipework and the MET. If its less than 1666 ohms then no supplementary bonding is required. If its more than 22000 ohm, its not an extraneous conductive part. If its between, supplementary bonding is required. You most likely don't need it.

Your bonding, if required, should be connected to the shower earth terminal. Not to the gas pipe or water pipe or MET. It should be 4mm.

Are you an electrician or DIYer?

Correct, use 10mm cable instead when going between any insulation.

Your shower will take approx 41A.

If the insulation is more than 100mm deep, your 6mm cable is only rated for 27A running under insulation, a 10mm would be 36A.

For insulation less than 100mm, 6mm will carry 34A, 10mm will carry 45A.

Can you not run the cable on top of the insulation? If not, it needs sorting.

What circuit protective device is protecting this cable?

Get an electrician.