My cable run from consumer unit to shower is 13 metres. I have 6 metres of 16 mm T & E going spare as well as 13 metres of 10 mm T & E. Is there anything against running the 16 mm cable to the loft and running the remaining 4 metres in 10 mm cable using the apprpriate spltter box. Or should I stick with 10mm and scrap the 16mm cable which would be a shame. Shower is Mira 9.8Kw.
I'd always stick with the same CSA of cable throughout a circuit like this.
10mm CSA is okay for this shower.
You are aware of the installations of electrical circuits/equipment in special locations, is deemed notifiable work under part p of building regs?
The regulations clearly state 434.2 a device providing protection against fault current shall be installed at the point where a reduction in the cross-sectional area or other change causes a reduction in the current-carrying capacity of the conductors of the installation. There are exceptions.
As 42.6A the 10mm will likely take the current according to the run. Do note reduction in current-carrying capacity so if for example the cable went through insulation it would be permissible to increase the csa for that part of run.
Also remember the MCB has to protect the cable and you can't buy a 42.6A MCB so depending on make either 40A or 45A and volt drop (I would guess around 2.4v well within limits) and ELI will need to match.
So if you were to use both cables I would have considered the reverse to what you have proposed and use 10mm to loft and 16mm within loft. However any joint may cause problems and I would avoid joints when ever possible.
Do remember if you are fitting cable it is up to you to measure the earth loop impedance etc and to enter all reading into the certificate which you must issue. And of course then present to whoever is issuing the completion certificate. It is not a case of this will do lets just stick it in. And considering the cost of LABC inspection if it were my job for the few pounds it costs I would buy 16mm for whole run. Just in case you want to use a bigger shower or add insulation in the future. The £100+ fee means one only really wants to do the job once.
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