Cu For Storage Heaters: Advice Would Be Much Appreciated

[TomMcQ]

I might have 4 storage radiators to install in the next week or two. I don't have any details of the job as yet but I'm guessing it might involve a separate CU / time switch / contactor arrangement. Not having done this before, I'm hoping one of the wiser heads on here might take a look at the sketch I've done (link below) and check that I've understood the basic wiring arrangement of the CU properly (or not as the case may be) and point out if and where I've gone wrong.

http://i1341.photobu...iringSketch.jpg

What I'm going for is a 5 amp CPD protecting the switching circuit; then the time switch controlling a 4-pole contactor that will achieve single-pole switching on each of the 4 loads. The load circuits each being protected by its own CPD downstream of the contactor.

A couple of specific questions about this:

1. I know there has to be an air gap between the contactor and the adjacent MCB, but what about the time switch? Do I need a gap there too?

2. As I understand it, contact bounce is a non-issue with resistive non-electronic loads but again, this is new territory for me so I'd be grateful for confirmation that this is indeed the case (or not?).

Thanks in advance,

Tom.

 

[SLIPSHOD & SLAPDASH]

Teminal 4 of the timer should be coonected to term 1 as its not fused at present

 

[SLIPSHOD & SLAPDASH]

The rest seems ok but none of this may be needed. NOrmaly one contactor would be fitted that feeds the heating board It also depends on what the DNO supplies you and you dont have to do anything except leave tails from the board

 

[NozSpark]

I've done this kind of thing on a submain that has a E7 tariff,,, I switched the supply to the MCBs

 

[Revved Up Sparky]

+1, Slipshod

In all the storage heater installs I have done over the years the DNO (North Wales) has always provided the equipment to supply storage heaters, nowadays usually by means of a teleswitch and dual tariff meter. All you have to do is install radial circuits, usually 2.5mm (based on individual loads of 850W - 3.4KW) protected by 16A MCBs/ RCBO's. I would use a 6 way CU to allow for future additions.

 

[TomMcQ]

Thanks guys, especially Slipshod for picking up on the timer terminal. Much appreciated!

Hopefully, as you say, I won't have to go down this route, but at least I can approach it with a bit of confidence now if it that's what it comes down to.

Thanks again,

Tom.

 

[Apache]

We have storage heaters both at home and work and both just come of a secondary supply from the meter that is only live on the cheap rate.

The timer wouldn't work as for 17 hours a day there'd be no power! (I suppose if you insisted on only having a single CU for everything this is the only way you could do it).

Just to note that the 7 hours (with us anyway) varies a little and does not change with BST so until the clocks change at the end of the month mine runs about 1.10am-7.50. In winter it comes on just after midnight. I watch it carefully as I run things like the washing machine, dishwasher and tumble dryer only on the cheap rate so stay up until it comes on. From where I am sitting now I can see a neon for a storage heater that illuminates when the eco 7 switches on.

If you set the power to the storage heaters to come on midnight to 7 they will get a big bill in summer if it does like ours!

(also if they rely on storage heaters likely they will have a hot water tank with electric immersion for hot water - so you might want another way on your board)

 

[TomMcQ]

Good tips, Apache, thanks, but I don't think there's going to be a secondary supply available. From what I know of the job so far, it sounds like the guy is planning to run the storage rads on standard rate off a single tariff meter. Crazy, I know, but it's his money. The other thing is that the install has already been started and all the kit and caboodle is already on site (the previous spark did a runner for some reason). From how it was described to me, it sounds like I'm either looking at switching the supply to the heating board like Slipshod and NozSpark suggested or as per my original scheme. However, thanks to those who've contributed to this thread, at least I'm prepared for either eventuality. .... and, who knows, maybe I can even talk the guy into looking at a more sensible/economical option? ... yeah, right, and there goes another one of them pesky flying pigs ...

 

[revjames]

I used to install these for the DNO back when they did that sort of thing. As Revsparks says teleswitch and dual tarrif meter. We did some as part of a rewire and in such cases fitted a contactor and the associated MCBs inside the consumer unit with the contactor being controlled by the teleswitch.

 

[Revved Up Sparky]

........I run things like the washing machine, dishwasher and tumble dryer only on the cheap rate so stay up until it comes on.

Clever ! ...... so did you wire sockets off the off peak consumer unit ?

 

[Steve3948]

Why would you wire sockets on the Off Peak board. On E7 after midnight or around that time all units are recorded at cheap rate, the tele switch gives the timed output during the cheap rate so that the storage heaters are not fed all day. So using washing machines and tumble dryers during the cheap rate saves money.

The DNO used to state that you had to have at least 1 Heat Unit to qualify for E7.

With E10 I'm not sure, some do Super Deal and Flexi-heat where you get the afternoon boost but that's only on the timed output.

A White meter which separate just gives a timed cheap rate output to items connected to it.

That's how it used to work, unless things have changed and I'm not aware of it.

 

[Revved Up Sparky]

Why would you wire sockets on the Off Peak board. On E7 after midnight or around that time all units are recorded at cheap rate, the tele switch gives the timed output during the cheap rate so that the storage heaters are not fed all day. So using washing machines and tumble dryers during the cheap rate saves money.

Thanks for that Steve. Somehow I never realised that !. I thought it was only the off peak board that went onto the cheap rate.

 

[Apache]

Clever ! ...... so did you wire sockets off the off peak consumer unit ?

No!

 

[Revved Up Sparky]

No!

Ha ha OK Steve already put me right on that ! :Applaud

 

[NozSpark]

Thanks for that Steve. Somehow I never realised that !. I thought it was only the off peak board that went onto the cheap rate.

Some (and that is a very very small few) do only supply the off peak board with cheap rate electricity... I have only seen 1 like that though

 

[Revved Up Sparky]

Some (and that is a very very small few) do only supply the off peak board with cheap rate electricity... I have only seen 1 like that though

Thanks Noz. I'll scoob ya for that when I get more scoobs. I don't feel such a fool now lol.....

:Salute

 

[ProDave]

Clever ! ...... so did you wire sockets off the off peak consumer unit ?

In my previous house, we kept the E7 long after the storage heaters were removed, and had a few "off peak" sockets in the kitchen for the washing machine, dishwasher and tumble dryer.While ANY socket will get the cheap rate with E7, you would have to have a washing machine with a built in start timer, or wait up until gone midnight to turn it on. The dedicated off peak sockets would power up at night and the machines would start.

It was usually the much older "white meter" tarrifs that only supplied cheap rate to just the heaters. These had two physically seperate meters, rather than one dual rate meter.

 

[batty]

Good tips, Apache, thanks, but I don't think there's going to be a secondary supply available. From what I know of the job so far, it sounds like the guy is planning to run the storage rads on standard rate off a single tariff meter. Crazy, I know, but it's his money. The other thing is that the install has already been started and all the kit and caboodle is already on site (the previous spark did a runner for some reason). From how it was described to me, it sounds like I'm either looking at switching the supply to the heating board like Slipshod and NozSpark suggested or as per my original scheme. However, thanks to those who've contributed to this thread, at least I'm prepared for either eventuality. .... and, who knows, maybe I can even talk the guy into looking at a more sensible/economical option? ... yeah, right, and there goes another one of them pesky flying pigs ...

When he gets his first bill he will come back begging you to put things right.

 

[NozSpark]

Good tips, Apache, thanks, but I don't think there's going to be a secondary supply available. From what I know of the job so far, it sounds like the guy is planning to run the storage rads on standard rate off a single tariff meter. Crazy, I know, but it's his money. The other thing is that the install has already been started and all the kit and caboodle is already on site (the previous spark did a runner for some reason). From how it was described to me, it sounds like I'm either looking at switching the supply to the heating board like Slipshod and NozSpark suggested or as per my original scheme. However, thanks to those who've contributed to this thread, at least I'm prepared for either eventuality. .... and, who knows, maybe I can even talk the guy into looking at a more sensible/economical option? ... yeah, right, and there goes another one of them pesky flying pigs ...

Here's a pic of one that I did

 

[sellers]

A handy hint with your storage heaters, install galv conduit to run your cables in the walls. Therefore you won't need RCBO's.

Its hardly worth RCDing all the circuits for the sake of 4 300mm chases.