by ericmark »
Mon Apr 21, 2008 8:58 am
2) Assuming the 6mm² cable is PVC
Ref Ref Ref Ref Ref Ref
100 101 102 103 A C
34 27 35 23.5 32 47
As you can see according to how the cable is run the amps is can carry vary in watts this becomes:-
7820 6210 8050 5405 7360 10810
Even the smallest shower may overload the cable. Because showers are used for such short times a small overload you may get away with so 7.5Kw on a 32 amp MCB is about the max (Ref C is direct in masonry and although it may travel part way like that 100 and 102 clipped to wooden joist and in stud wall are more likely limiting factors) If the cable runs through a wall with insulation and is not clipped or if in loft with insulation above level with joists then 6mm² will not run a shower. People have got away with a 8.5Kw shower on 32 amp MCB but if they have anything more than very short shower it will trip and in the end the trip itself will fail.
The 9.5Kw showers need 16mm² really but you can get away with 10mm² for short showers. Also as one uses 40, 45, or 50 amp MCB’s you need to be sure your whole supply can cope as some houses have only 60 amp supply. I have seen in old houses 6mm² tails from meter to consumer unit. Remember all electrical installations should be tested and new circuits and work in bathrooms and kitchens often needs Part P there are links in Projects section.
1) As to lamp I would retain existing rose but re-position above ceiling then feed new lamp from the flex. i.e. use old rose as junction box. Strictly speaking its not allowed as you don't need a tool to open a ceiling rose and it only has special dispensation when used as ceiling rose. But how many people are really going to go into your loft and mess with it?
