Questions on: Immersion switch replace with timer

[SimonH2]

Why does this only switch LED's up to 80w ?

That's a very good question - I can't think of a good reason, especially as it's rated to switch 4A inductive.
The only thing I can think of is that LEDs are basically driven by switch mode power supplies, and the front end of these are basically a bridge rectifier followed by a capacitor. These give a very high current spike at switch on while the cap charges. But I think such a basic design hasn't been allowed for some time, and even so, restricted to 1/3A ?

 

[NickNock]

Wow! Thanks you all for the time and thought you've given to replying.
By chance yesterday I met an electrical engineer that gives toolbox talks and training to others.
Doesn't mean he is any good of course, or that he knows the regs inside out but I do know he has to give presentations on the regs.
He claims that the timer itself replaces the switch and as there is the dedicated MCB at the consumer unit that is all that is required. He also said that the flex does not need strain relief (!!) and that it can exit out of the plasterboard for instance, adjacent to the timer as long as there are no sharp edges that increase the risk of the flex being damaged. This seems nuts to me, but he assured me that is all the regs demand. He suggested that best practice would be a flex outlet plate between the timer and the flex but not actually required by regs.
I wander what you all think to that!?

 

[oldbutnotdead]

Why not stick the timeclock down near your consumer unit? (assuming there's room and you can identify the supply to the immersion heater). That way you can keep your local isolation and not have to traipse up to the back bedroom if you fancy an unscheduled burst of hot water.

Back to the original question- your flex 'poking out' of the plasterboard will look shoddy and would be indicative of minimum effort (ie work may be compliant but it may not be good).

 

[NickNock]

Why not stick the timeclock down near your consumer unit? (assuming there's room and you can identify the supply to the immersion heater). That way you can keep your local isolation and not have to traipse up to the back bedroom if you fancy an unscheduled burst of hot water.

Back to the original question- your flex 'poking out' of the plasterboard will look shoddy and would be indicative of minimum effort (ie work may be compliant but it may not be good).

Thanks Oldbutnotdead,
fortunately the consumer unit is in the garage (frees space indoors).
I agree about the shoddy appearance. If I were a surveyor I'd think "if this, then what else?" and start really digging for failures in the whole building.
Nick

 

[SimonH2]

Sorry if I missed it being stated, but is the existing switch flush or surface mounted ?
If it's surface, then as suggested, use another surface box and put a gland in the side of it for strain relief.
As to isolation, bear in mind that the MCB in the CU is almost certainly only single pole, so a fault in the immersion could prevent the RCD being reset unless you have double pole isolation somewhere.

 

[endecotp]

summertime immersion control (use boiler in winter).

Why do you not use the boiler in the summer?

 

[Iggifer]

Wow! Thanks you all for the time and thought you've given to replying.
By chance yesterday I met an electrical engineer that gives toolbox talks and training to others.
Doesn't mean he is any good of course, or that he knows the regs inside out but I do know he has to give presentations on the regs.
He claims that the timer itself replaces the switch and as there is the dedicated MCB at the consumer unit that is all that is required. He also said that the flex does not need strain relief (!!) and that it can exit out of the plasterboard for instance, adjacent to the timer as long as there are no sharp edges that increase the risk of the flex being damaged. This seems nuts to me, but he assured me that is all the regs demand. He suggested that best practice would be a flex outlet plate between the timer and the flex but not actually required by regs.
I wander what you all think to that!?

Well he doesn't know what he's talking about: (Reg numbers may have changed slightly, but regs are still valid)

Strain relief: 522.8.5 (522.8 deals with mechanical stresses)

Every cable or conductor shall be supported in such a way that it is not exposed to undue mechanical strain and so that there is no appreciable mechanical strain on the terminations of the conductors, account being taken of mechanical strain imposed by the supported weight of the cable or conductor itself

Isolation: 554.3.3 (554.3 deals with immersed water heaters)

The heater or boiler shall be permanently connected to the electricity supply through a double-pole linked switch which is either separate from and within easy reach of the heater or boiler or is incorporated therein, and the wiring from the heater or boiler shall be connected directly to that switch without the use of a plug and socket-outlet

 

[stillp]

There is also a reg requiring good standards of workmanship. If he thinks the flex exiting through a hole in plasterboard is good workmanship, then I wouldn't let hom change a light bulb, let alone anything else.
The 'regs' are just a standard. They list some of the things that are allowed, and many of the things that are not allowed. They are not a text book, nor are they a substitute for thinking, or for good workmanship.

 

[kai]

That immersion switch is designed to be mounted on, say the Landing or Hallway wall, with a further cable tun to the immersion cupboard, where a DP switch with flex grip is provided in order to feed the immersion flex to the element. Is is NOT designed to have flex wired directly into it - the terminals may have been designed for solid core cable, and NOT flex, hence the missing flex gripper. It is far easier to set and adjust the timer when it is in an easily accessible position in good light.

 

[EFLImpudence]

That immersion switch is designed to be mounted on, say the Landing or Hallway wall, with a further cable tun to the immersion cupboard, where a DP switch with flex grip is provided

Well, if that's the case he can wire the timer before the switch anywhere - but I wouldn't.

The only problem is the cable restraint - not exactly an insurmountable problem, is it?

 

[Iggifer]

Nope, as I linked to, P(Pyro)Clips will do the job perfectly.

Or a surface box with cable gland.

 

[JohnD]

Why do you not use the boiler in the summer?

My guess it is because he doesn't know that energy from electricity costs about four times as much as energy from gas.

 

[NickNock]

Thank you all for your ideas and comments.

Iggifer
Seems you are right, he can't do. Those references are invaluable, many thanks for digging them out, not sure why my pdf viewer's search did not turn up those.

Stillp
Thanks, yes I agree and appreciate this, that standards are not necessarily regs, nor exhaustive.

Kai
Sadly my GF won't have the timer on the landing walls so it is confined to the airing cupboard (I've left a thermometer in there to check that it's within the timer operating limits). I can't imagine many folk would want it mounted in clear sight as it's ugly.
The timer is in effect a double pole switch it seems, and manual override button giving permanent off, permanent on , and timer positions.

SimonH2
Existing is flush, and I've got another flush pattress.
I will get a double pole RCD to replace the single pole MCB in the consumer unit.

EFLImpudence
I've now bought a flex outlet plate. Though I liked the 'P' clip idea, based on the aesthetics issue, thought it would attract less attention from a surveyor.

Endecotp and JohnD
Our gas boiler is ancient and inefficient. I've added extra lagging on top of the existing yellow urethane foam cylinder insulation, and want to use try using the immersion more as an environmental measure than a cost equivalent. I'll measure the energy usage using each fuel, and assess the carbon footprint and the cost. We are not in a position yet to replace the boiler though looking at that in 2-3 years. I'm prepared to pay extra for the few summer months if it's
a) more environmentally friendly,
b) prolongs the boiler life a bit,
c) saves the kitchen / utility area from getting so hot in the summer
d) all year round when we have have guests staying over we can boost the hot water and not forget to turn the immersion off after.

I reckon all these benefits are worth paying a bit more for. My GF has to have the heating on for all but the warmest months (usually about Sept - April) due to health reasons. Last year I had TRVs fitted to all rads when the boiler was being serviced so at least only a few rooms are like a sauna.

Thanks again everyone.
I feel more confident in my proposal in my OP. with the addition of the DP RCD in the consumer unit. I would like to have belt and braces a fused switched plate just in case the timer fails but it is double insulated and CE marked; there just isn't wall space for it and it seems from comments here and the references Iggifer found, it isn't strictly necessary.

all the best, Nick

 

[EFLImpudence]

Do not have a fused switch for the immersion; just a switch.

 

[NickNock]

Do not have a fused switch for the immersion; just a switch.

Understood and thank you.