6kw heater

[mur312]

a 6kw water heater what sizeof cable should my sparky use 10m run approx

 

[ericmark]

Not enough information it will likely be between 4 and 10mm but the method of installation is all important. Reference Method 103# (in a stud wall with thermal insulation with cable not touching the inner wall surface) would need 10mm cable but Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) would only need 4mm and both are if 70deg C cable is used. 90 deg cable changes again.
In real terms you can't use 4mm cable as although your using 26A you can't get a 26A overload so likely you would need to use 32A overload to protect so in real terms either 6mm or 10mm according to route.
I wonder why you ask. If you getting an electrician he should tell you what size you need! He will have the BS7671:2008 book which gives all the cable sizes and tells how to calculate for specials.

 

[MarkBarl]

Your sparky should know. It depends on many things, such as the length of run, where it is running e.g under insulation or clipped to wall etc. these tables give some useful information. for 6KW you are looking at about 26amps (Power = Voltage x Current) . From the table 4mm might be suitable in certain circumstances, though I would suggest 6mm would be better with a greater safety margin.