Customer called - smoke from the cu. That's what I found:
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The shower currently is Mira -10.8kW. The cable is T&E 6mm, protected by BS3036-32A. It seems that in some point they upgraded the shower but not the circuit. The terminals were loose both in CU and the DP switch. There is no RCD protection and no bonding to water/gas.
I wanted to double check with you guys: The shower circuit should be upgrade with 10mm( is about 15m run under the floor boards and in the loft) and 45A fuse/MCB. Also RCD protection... Or other option would be 9kw shower.
Even fitting a 9K shower would still need a new circuit IMHO.
So 10mm, possibly a 50A MCB if staying 10800.
ALSO..
With something as bad as that I would be strongly advising the customer to have a full & thorough PIR of the whole installtion...
As well as the remedial works to fix the fault.
I think I would also put a covering letter with any costs I give...
Dear Mr IwantToBurnMyHouseDown
Whilst investigating your shower circuit fault on dd/mm/yy I was very concerned about the standards of the installation work and poor circuit design. (evident by the excessive overheating of the fuse box). I consider it my duty of care to advise you in writing of some important issues you need to consider.
1. Basic school science teaches that Power(watts)=Volts x Current(amps). Your 10.8kw shower is 10800watts and the manufactures normally quote power ratings 240v supply.
2. A simple calculation tells us 10800watts/240v = 45amps. (this was probably quoted on the box or in the manufactures instructions). All components of the circuit must be able to carry this current rating or overheating and damage will occur.
3. The cable installed for your shower is running at the very top of its design capacities. (Wiring regs BS7671 suggest 46A if in open free air clipped on the surface of a wall)
4. As part of you cable run is concealed, I am at a loss to understand how any competent electrician would install such a high power shower onto this circuit. To be polite I would call it exceptionally poor design, verging on the dangerous!
5. A correctly designed and installed shower will not cause the overheating evident at your fuse box, with the associated risk of fire and serious damage to property.
6. I have enclosed costings for appropriate remedial works to bring this circuit into compliance with current wiring regulations to allow safe operation. I would not advise putting the shower back onto the existing fuse board, as I am concerned about the overheating damage.
7. In addition to the immediate remedial work required, I would also recommend that a full inspection and test of all remaining circuits is carried out at your earliest convenience. I am concerned that if corners have been cut with installation standards on a high power item, then maybe more corners been cut on other circuits within the property.
8. Wiring regulations recommend that domestic properties are inspected & tested every 10 years or change of occupancy. If you do have a Periodic Inspection Report dated within the past 10 years please ignore my above point. However I could not see any label at the fuse box indicating this has been done.
9. As we discussed it would also be good practice to plan on updating your fuse boxes to modern design with the Trip-Switch fuses & RCDS. These would provide a greater level of safety to you and you family. I have included costings for this as well. However a full inspection would be needed first to identify any other potential dangers or hazards that you are not aware of.
Should you require any further information don't hesitate to call me or contact one of the recognised trade bodies Napit/NICEC/ELECSA/BSI, most have websites with customer support and advice pages or contact numbers.
Regards
Very Concerned Sparky
ut the kettle on
