Wiring defect

[Bert]

Just installed 9Kw instant water heater serving cloakroom basin. 15 M run of 10mm cable back to domestic fuse board on to 40 amp fuse.
Trouble is, when the hot tap is turned on and the heater energises the house lights go dimmer??

 

[Spark123]

This will be to do with the supply characteristics, there is little you can do about it other than contact your eleccy board. The further away you are from the substation, the worse the problem gets. Have you got a multimeter? What is the standing voltage at the CU before and after the water heater energizes? The voltage should remain between 216.2v and 253v. If the voltages remain between these tolerances then the eleccy board probably wont do anything anyway.

 

[jonesy1]

hi bert, have you got fuses or mcb's if mcb's the max length of cable 10mm t&e with a 4mm cpc (earth) is 32m however if you have re-wirable fuses on the same cable then you can run upto 50m, just one more thing is the fuse or breaker the closest to the main switch cus that can effect your lights.

good luck

 

[Big_Spark]

Bert, this is likely caused by "eddy currents" being induced on the busbar in the CCU. The higher rated breakers should be installed nearest the main switch and in order.

Supply issues can cause this, but they shouldn't as such dimming is caused by Voltage drop. Whilst there could be issues in this field, I would think it more likely caused by a combination of wrongly installed breakers (not in sequence of load) and possibly loose connections causing a higher draw on the supply causing the voltage to dip further.

One thing I would suggest that you do is measure the voltage at the INPUT side of the Main Isolatoir in the Consumer Unit. In all liklehood it will be about 238V, but it could vary from 216V to 253V. If you measure it and it is below 230V, then you have a supply issue, but above this the voltage drop is unlikely to effect the lights unless the breakers are not installed in sequence and eddy currents are being induced on the busbar.