What rating shower heater on 6mm T&E cable/

[DavidM]

A friend is letting us use their 17th century cottage in Cornwall for a few days this coming holiday, in exchange for me fitting a replacement for her very old electric shower heater, which is leaking and beyond economical repair. This existing shower is fed via approx 3.5m of 6mm T&E cable, via a ceiling mounted, pull cord, isolatiing switch, and the cable is buried in the wall for probably 2.5m of its total length. Don't know until I get there what size fuse/mcb is fitted in the CU. What is the maximum rating (kw) shower I can connect to this size cable? Thanks, David. ( Part pee.....yeah, I know!!)

[Dave Plowman (News)]

[Andy Wade]

If clipped-direct conditions apply to the whole cable run (i.e. no thermal insulation, no grouping with other cables, no conduit or trunking) you can take the current rating to be 47 A, which means a maximum of 10.8 kW at 230 V, supply and fusing permitting.

It sounds as if you are doing a direct replacement, which is not notifiable. It would of course be prudent to carry out insulation resistance and Zs test on the circuit though, as well as testing any RCD that may be fitted. Also check that the supplementary bonding is OK, particularly if there's no RCD.