David Hansen wrote:
On Mon, 17 Mar 2008 14:19:42 -0000 someone who may be "Tim Downie"
wrote this:-

Nope. They're just glorified electric kettles.

Incorrect. Such heaters merit a special section of the Wiring
Regulations, at least they did in the 16th Edition. There are a
number of requirements to install them safely. I have no intention
of regurgitating them.

You're presumably referring to regulation group 554-05 in the 16th ed.
This does not apply to ordinary domestic electric showers since they
have _insulated_ elements.

And the 17th ed. does have similar requirements - sections 554.1 for
electrode boilers and heaters and 554.3 for uninsulated immersed
elements - all quite irrelevant to domestic shower units.

554.2 - headed "Heaters for liquids or other substances having immersed
heating elements" - does apply though. This section only has one
regulation:

544.2.1 Every heater for liquid or other substance shall incorporate or
be provided with an automatic device to prevent a dangerous rise in
temperature.

--
Andy