Immersion Heater (follow on)

Checked it out tonight and found that it was the switch in the airing
cupboard that had failed on the neutral side.
The circuit is fed by a 16amp MCB. The switched spur that has failed is a
Compactum.
Any recommendations for a replacement (thinking MK)
Also it is wired in PVC Flex between the switched /fused outlet and the
immersion heater. Is there something better (years ago I would have bought a
length of asbestos insulated flex.)
Reply to
John
Contactum I think you'll find. Replace with another Contactum - perfectly good make. The flex to the element is probably "butyl" heat resist, and should be retained, or replaced with the same. It's generally 85 centigrade rated.
Reply to
scdavies01
Contactum I think you'll find. Replace with another Contactum - perfectly good make. The flex to the element is probably "butyl" heat resist, and should be retained, or replaced with the same. It's generally 85 centigrade rated.
Thanks - perhaps it is butyl - but I will replace it as the ends seem a bit brittle.
Incidentally - do I need a fused (13 amp) outlet - or is it better to fit a 20 amp switch?
Reply to
John
I prefer a 13 amp local fuse, and the MCB should be RCD protected at the Consumer's Unit.
Can you find any reg that says you need an RCD for this? (assuming not a TT supply)
Adam
Reply to
ARWadworth
Contactum I think you'll find. Replace with another Contactum - perfectly good make. The flex to the element is probably "butyl" heat resist, and should be retained, or replaced with the same. It's generally 85 centigrade rated.
Of course - Contactum as in Contacts. Like MK originated from "Multi -Kontact" in the days of round pin plugs.
Reply to
John
On Jan 8, 10:02=A0pm, "ARWadworth" wrote:
No. But I would take a best practise, belt and braces approach to the job personally
Reply to
scdavies01
No. But I would take a best practise, belt and braces approach to the job personally
My concern is that a switched spur unit has failed (and it was a replacement) - A 20 amp switch should carry the load better without stress - but is it appropriate to rely on the 16 A MCB (without a 13amp fuse)
Reply to
John
I would hazard that the spur has failed because the terminations weren't done properly. If you want to do the job properly, tin the strands of the butyl, as stranded conductors can be problematical. You say that the cable is "brittle" at the ends, implying heat which may (or may not) be due to an HR termination. A 13A switch should be fully capable of carrying the current demand of a domestic Imm Heater. As I said earlier, I prefer a local fuse, MCB and RCD.
Reply to
scdavies01
I would hazard that the spur has failed because the terminations weren't done properly. If you want to do the job properly, tin the strands of the butyl, as stranded conductors can be problematical. You say that the cable is "brittle" at the ends, implying heat which may (or may not) be due to an HR termination. A 13A switch should be fully capable of carrying the current demand of a domestic Imm Heater. As I said earlier, I prefer a local fuse, MCB and RCD.
I thought I heard that tinning the ends of flex was a real no-no (although it would seem a good idea)
Reply to
John
Never heard that myself, if you don't fancy it, twist it well and then make your termination. I find a drop of electric glue invaluable if I have to mate solid and stranded in the same slot.
Reply to
scdavies01
On second thoughts, I'm trained and practised in soldering, but considering the butchery I've seen, usually because of too cool irons, maybe you should disregard my earlier post. Just make sure you've got a good joint. I'm doing a job at the moment which requires 2 X 9 Kw electric boilers. I've got to source appropriate switch-gear for them tomorrow. Should be fun.
Reply to
scdavies01
Tinning the ends of flex before terminating in a screw terminal is a no-no.
Solder exhibits a phenomenon known as "cold flow". When you tighten the screw, you put pressure on the solder. The solder will tend to "creep away" (i.e. cold flow) from the point of pressure (i.e. the end of the screw) which in time will make the joint loose.
Copper does not cold flow (or at least not to the same extent).
Reply to
Rumble
Never had a problem with that in practise, though touch and feel when making connections is important.
Will look up cold flow and see what I can find out. Interesting.
Reply to
scdavies01
On 8 Jan,
A rarely used immersion heater could be leaky enough to cause nuisance trips, but fine after being used. I'd leave it off the RCD side unless on a TT system.
Reply to
<me9
On 8 Jan,
The solder can creep and result in a HR joint. Better to use a proper crimped termination if you have to mix flex and cable in the same terminal.
OTOH, I can't see any necessity to include both in the same slot anyway.
Reply to
<me9
formatting link
brittle fracture, creep deformation does not occur suddenly upon the application of stress. Instead, strain accumulates as a result of long-term stress. Creep deformation is "time-dependent" deformation.
[...] Plastics and low-melting-temperature metals, including many solders, creep at room temperature as can be seen marked in old lead hot-water pipes."
Reply to
Rumble
In article , snipped-for-privacy@btinternet.com writes:
No you never do this. The solder creeps and contact pressure is lost, resulting in a bad connection. Ideally you crimp on a bootlace ferrule, but most people haven't got the kit to do that, so you just have to be careful to make a good connection with the strands. (You can solder on a bootlace ferrule).
RCD not required here, and not a particularly good idea for this particular load. Local fuse is a source of heat itself, and a couple more potential bad contacts. 16A MCB is fine by itself for protection. Use a 20A double pole switch.
Reply to
Andrew Gabriel
on a 16A MCB protected circuit either should be fine, but a 20A switch is unlikely to have a cord grip for the flex to the immersion heater.
Owain
Reply to
Owain

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