Extending a shower cable

[Chorlton1]

I'm putting new insulation in the loft. Existing shower cable is just clipped to the ceiling joists with approx 100mm insulation on top - it's not long enough to put above the extra new insulation, which will be 200mm in addition to existing.

I've done some calcs and with the extra insulation the cable (10mm) is not adequate.

Is it acceptable to increase the cable length by using something like 60A junction boxes and putting extra length of cable in the middle? If I do this I intend to move the cable away from insulation by clipping it to the underside of the roof joists.

 

[JonoPashley]

What size is the shower and how long is the cable run from the CU to the shower?

 

[Chorlton1]

it's a 9.8kW shower and the run is approx 13m about 6m of which is in the loft. It terminates at the CU with a 45A MCB - the unit has RCD protection.

As far as I can tell it's 10mm cable.