On 15/12/2020 16:30, Robin wrote:
On 15/12/2020 11:08, wrote:
On 14/12/2020 15:22, wrote:
On 13/12/2020 15:17, Robin wrote:
On 13/12/2020 12:37, wrote:
One for our resident certified electrical installers ...
I want to add a spur to feed a wall-mounted smart heating
controller, which has a PSU as part of its wall-mount kit. I don't
want to have a fused spur plate on the wall so am planning on
putting an in-line fuseholder in the back-box for the wall-mount
kit. I don't have any concerns about whether this is safe, but I
can't decide whether it meets the regs or needs any specific
labelling.
Can anyone here provide the answer?



I'm not certifiable (yet) but have a couple of questions and comments.
Perhaps I'm heading in the "certifiable" direction ;-)

First, what if anything do the manufacturer's instructions require?
There's nothing about protection

Second, I am not clear what - if any - means of local switching and
isolation you end up with.Â* An unswitched FCU to BS 1363-4 counts
(Table Â*Â* 537.4 in the regs): you can remove the fuse without risk
to life and limb.Â* But what you propose ain't to BS 1363-4 and
AFAICS could only remove the fuse by opening up the back box.Â* So I
think that's a problem.

You may be right but the fuse would only need replacing if the PSU
fails, and that is in the back box. All connections would be
insulated and I found an inline fuseholder with appropriate
protections (although I can't find it now) so I think it meets the
intent, but maybe not the letter, of the requirements.
Following that thought chain, the fuse could be non-replaceable and
considered part of the PSU. So something like
https://www.ebay.co.uk/itm//323268286316 in two layers of heat-shrink.

If the manufacturer lays down no requirements and your only concern is
to protect the cable (ie no local switching or isolation required) then
ISTM you could just extend the ring final circuit to the PSU and avoid
the need for a fuse altogether.Â* Well, assuming the PSU's connectors can
take 2 x 2.5 mm2 copper

True, although that would be a case of something being "legal" but not
sensible.