The immersion heater stopped working the other day and I tracked it
down very quickly to the timer/controller, so I got a new one from
Screwfix ( http://www.screwfix.com/p/digital-we...on-timer/92265
). Pretty much identical to the previous one with slightly simpler
wiring. Still has a similar lack of provision for connecting the
earth though, which seems dodgy.

Just for a change (!) I read the instructions, which very clearly say
that the connection (a screw terminal, just like a bit of choc block)
should only be made with solid core cable and not stranded. This
seems a bit odd, as the connection would (it seems to me) come from a
switched outlet to the timer, then go on to the immersion heater
element, both of these needing heat-resistant flex.

So, to my questions: Does this mean the wiring should go - Switched
outlet - flex - junction box - solid cable - timer - junction box -
flex - element? (seems a bit over board to me, but I can't envisage
feeding solid cored cable out of the outlet or to the element)
If so, what sort of junction boxes would be good? (if a choc block
type of screw terminal shouldn't take stranded flex at the timer,
surely the same applies in a JB, or am I missing something?

I probably wouldn't usually give this much thought but the problem was
caused by what looks like the flex coming from the old timer burning
out. Presumably there had been some mechanical strain on the flex
(and there is no strain relief on these timers) that broke a few
strands, leading to increased resistance etc etc.

Any views from the experts?

Cheers

In article
,
GMM wrote:
I probably wouldn't usually give this much thought but the problem was
caused by what looks like the flex coming from the old timer burning
out. Presumably there had been some mechanical strain on the flex
(and there is no strain relief on these timers) that broke a few
strands, leading to increased resistance etc etc.

A timer would normally be fixed to the wall, so wired *before* the cord
outlet to the element. I realise this might make more work.

--
*Fax is stronger than fiction *

Dave Plowman London SW
To e-mail, change noise into sound.

On Jul 9, 3:07*pm, "Dave Plowman (News)" wrote:
In article
,
* *GMM wrote:

I probably wouldn't usually give this much thought but the problem was
caused by what looks like the flex coming from the old timer burning
out. *Presumably there had been some mechanical strain on the flex
(and there is no strain relief on these timers) that broke a few
strands, leading to increased resistance etc etc.

A timer would normally be fixed to the wall, so wired *before* the cord
outlet to the element. I realise this might make more work.

--
*Fax is stronger than fiction *

* * Dave Plowman * * * * * * * * London SW
* * * * * * * * * To e-mail, change noise into sound.

I take your point Dave and this one is fixed to the wall, although not
sunk in a back box (the terminals are under a shroud at the bottom, as
they would be for a flex to loop in and out). The unfortunate thing
(to me) is there don't seem to be any alternatives available in the
sheds/Screwfix, etc. (There might be some from other sources but I was
just trying to crack this off over the weekend.

In article
,
GMM wrote:
A timer would normally be fixed to the wall, so wired *before* the cord
outlet to the element. I realise this might make more work.

I take your point Dave and this one is fixed to the wall, although not
sunk in a back box (the terminals are under a shroud at the bottom, as
they would be for a flex to loop in and out). The unfortunate thing
(to me) is there don't seem to be any alternatives available in the
sheds/Screwfix, etc. (There might be some from other sources but I was
just trying to crack this off over the weekend.

To use flex into a connection designed for solid core, you need a ferrule.

--
*It ain't the size, it's... er... no, it IS ..the size.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
GMM writes:
The immersion heater stopped working the other day and I tracked it
down very quickly to the timer/controller, so I got a new one from
Screwfix ( http://www.screwfix.com/p/digital-we...on-timer/92265
). Pretty much identical to the previous one with slightly simpler
wiring. Still has a similar lack of provision for connecting the
earth though, which seems dodgy.

Just for a change (!) I read the instructions, which very clearly say
that the connection (a screw terminal, just like a bit of choc block)
should only be made with solid core cable and not stranded. This
seems a bit odd, as the connection would (it seems to me) come from a
switched outlet to the timer, then go on to the immersion heater
element, both of these needing heat-resistant flex.

So, to my questions: Does this mean the wiring should go - Switched
outlet - flex - junction box - solid cable - timer - junction box -
flex - element? (seems a bit over board to me, but I can't envisage
feeding solid cored cable out of the outlet or to the element)
If so, what sort of junction boxes would be good? (if a choc block
type of screw terminal shouldn't take stranded flex at the timer,
surely the same applies in a JB, or am I missing something?

I probably wouldn't usually give this much thought but the problem was
caused by what looks like the flex coming from the old timer burning
out. Presumably there had been some mechanical strain on the flex
(and there is no strain relief on these timers) that broke a few
strands, leading to increased resistance etc etc.

Could be, but also common is that the switched contact gets some
resistance after a while (particularly high current ones like this),
and conducts the resulting heat back to the connection, which then
burns the insulation (and might also cause connection deterioration).
With shower switches, it's probably 50/50 original poor connection,
verses switch contacts burning out (which is why I always recommend
getting a good quality switch for high current applications, and not
the cheapest on the shelf).

You need bootlace ferrules on the flexible conductors. You might
be able to buy a short length of high temp immersion heater cable
made up with ferrules on (not that I've looked as I would crimp
them on myself, but it seems like a common requirement).
Maybe a small electrical shop would make it up for you?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Dave Plowman (News) wrote:
In article
,
GMM wrote:
A timer would normally be fixed to the wall, so wired *before* the
cord outlet to the element. I realise this might make more work.

I take your point Dave and this one is fixed to the wall, although
not sunk in a back box (the terminals are under a shroud at the
bottom, as they would be for a flex to loop in and out). The
unfortunate thing (to me) is there don't seem to be any alternatives
available in the sheds/Screwfix, etc. (There might be some from
other sources but I was just trying to crack this off over the
weekend.

To use flex into a connection designed for solid core, you need a
ferrule.


http://www.tlc-direct.co.uk/Products/CTPINslashR.html

would probably do the job.

The OP would have to chop it down as the terminals on the timer are probably
very short.

--
Adam

On Jul 9, 8:33*pm, (Andrew Gabriel) wrote:
In article ,
* * * * GMM writes:





The immersion heater stopped working the other day and I tracked it
down very quickly to the timer/controller, so I got a new one from
Screwfix (http://www.screwfix.com/p/digital-we...on-timer/92265
). *Pretty much identical to the previous one with slightly simpler
wiring. *Still has a similar lack of provision for connecting the
earth though, which seems dodgy.

Just for a change (!) I read the instructions, which very clearly say
that the connection (a screw terminal, just like a bit of choc block)
should only be made with solid core cable and not stranded. *This
seems a bit odd, as the connection would (it seems to me) come from a
switched outlet to the timer, then *go on to the immersion heater
element, both of these needing heat-resistant flex.

So, to my questions: *Does this mean the wiring should go - Switched
outlet - flex - junction box - solid cable - timer - junction box -
flex - element? *(seems a bit over board to me, but I can't envisage
feeding solid cored cable out of the outlet or to the element)
If so, what sort of junction boxes would be good? *(if a choc block
type of screw terminal shouldn't take stranded flex at the timer,
surely the same applies in a JB, or am I missing something?

I probably wouldn't usually give this much thought but the problem was
caused by what looks like the flex coming from the old timer burning
out. *Presumably there had been some mechanical strain on the flex
(and there is no strain relief on these timers) that broke a few
strands, leading to increased resistance etc etc.

Could be, but also common is that the switched contact gets some
resistance after a while (particularly high current ones like this),
and conducts the resulting heat back to the connection, which then
burns the insulation (and might also cause connection deterioration).
With shower switches, it's probably 50/50 original poor connection,
verses switch contacts burning out (which is why I always recommend
getting a good quality switch for high current applications, and not
the cheapest on the shelf).

You need bootlace ferrules on the flexible conductors. You might
be able to buy a short length of high temp immersion heater cable
made up with ferrules on (not that I've looked as I would crimp
them on myself, but it seems like a common requirement).
Maybe a small electrical shop would make it up for you?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

I've never looked at ferrules like that but I'm sure it could be
sorted. I'm still a tad concerned, now that I've been thinking about
it, about the idea of having a flex (actually 2 flexes) dangling in
the airing cupboard with no strain relief. I guess I could clip it to
the wall or something, so a stray pack of bog rolls chucked into the
airing cupboard doesn't cause another problem. Funny how these things
get taken for granted until something happens........It was lucky
nothing caught fire, looking at the amount of scorching and the state
of the flex.