Emmersion heater

[kai]

The FCU and it's padlockable fuse holder is to satisfy the Electricity At Work Act 1989 - particularly as Plumbers are reasonably expected to work on the immersion - even economy seven dual supply systems.

Quoted from the Regulatations...

Means for cutting off the supply and for isolation
12.—(1) Subject to paragraph (3), where necessary to prevent danger, suitable means (including, where appropriate, methods of identifying circuits) shall be available for-
(a) cutting off the supply of electrical energy to any electrical equipment; and
(b) the isolation of any electrical equipment.

(2) In paragraph (1), "isolation" means the disconnection and separation of the electrical equipment from every source of electrical energy in such a way that this disconnection and separation is secure.

 

[HDRW]

isnt there a clock and 2 meters on economy 7?

That's one way of doing it - others are a clock and a 2-dial meter (which is what I have) and 2-dial meter with switching provided by a sub-carrier transmitted on the Radio 4 Longwave signal (198m I think).

The thing about having 2 immersion heaters is a technique which capitalises on having 2 rates, but isn't necessarily part of it - I just have a single immersion heater on a timeswitch and it stays warm enough through the day.

Or am i thinking of the old version that we had in our house with electric storage heaters we had 2 meters, 2 cu's, a mass of meter tails, then the REC came and rewired our street and took away the 2nd meter!

There was a previous system when storage heaters were very inefficient which had an afternoon "top up" period, so the storage heaters would get enough heat to carry on into the evening. Still didn't really heat the house, though! I can't remember what they called it, but it had two seperate meters and a hefty timeswitch to control the current through the second "cheap rate" one, which only ran the heaters - other electricity used overnight was at the expensive rate. It preceded Economy 7 (which originally had a single "white meter" with two dials).

how does the electric co know how much electric you have used at cheap rate if you only have the one meter and cu?

It can't!

im confused. if the clock switches over to cheap rate meter / cu at night, how do the circuits on the day cu work? does this sound stupid? sorry if its a really obvious answer but this is something thats always puzzled me!

On Economy 7 (at least the one I have), everything used during the cheap 7 hours is at the cheap rate - only the "cheap" dial on the meter is running, and switching between them is controlled by the REC's timeswitch, which is sealed. There is a seperate high-current switch in the timeswitch which powers the storage heaters, so you know that they only ever use "cheap" electricity. When morning comes, the timeswitch turns off the supply to the heaters, and switches the meter to recording on the "expensive" dial. To get my immersion heater to use cheap electricity, I have a seperate timeswitch next to it which I have to keep synchronised to the E7 timeswitch (it loses time during power cuts). That way I can override it if I need more hot water than is stored.

Cheers,

Howard

 

[ban-all-sheds]

To get my immersion heater to use cheap electricity, I have a seperate timeswitch next to it which I have to keep synchronised to the E7 timeswitch (it loses time during power cuts).

Why not use a contactor energised by the NSH circuit?

 

[Lectrician]

Best idea for this situation BAS - if installed and construsted properly.

 

[HDRW]

To get my immersion heater to use cheap electricity, I have a seperate timeswitch next to it which I have to keep synchronised to the E7 timeswitch (it loses time during power cuts).

Why not use a contactor energised by the NSH circuit?

A number of reasons:

1. I want to be able to switch it on /ad-hoc/ for situations when I need more hot water than usual during the day
2. The cable route from CU to airing cupboard is very awkward and I really don't want to have to run another cable
3. Having logged the water temperature in the tank over a period of time (using a PC with a temp. sensor and an analogue/digital converter) I find that the heater is only on for about three quarters of an hour when it heats the tank initially, then the thermostat trips and the temperature starts to drop off again. In normal circumstances, the thermostat doesn't kick in again that night, so the water is well below its peak temperature at the end of the cheap period. Consequently it's actually better to turn it on about an hour or so from the end of the cheap period, not at the beginning!

Cheers,

Howard

 

[ban-all-sheds]

Well - it seems to me that what you need is a much bigger CU to give you rail space for a PLC. Some timers, contactors and temperature sensors, and away you go.

Manual overrides? Pah!

 

[breezer]

a good plc will do all that in one (but wil stll need external sensor)

 

[HDRW]

Well - it seems to me that what you need is a much bigger CU to give you rail space for a PLC. Some timers, contactors and temperature sensors, and away you go.

Manual overrides? Pah!

Hey guys, it really isn't a problem! For the rare times I have to use the manual override, it's not worth trying to find another solution, and some of those times it would have to predict the future, so wouldn't work anyway!

Cheers,

Howard

 

[kevplumb]

why not better insulation on the cylinder

 

[HDRW]

why not better insulation on the cylinder

No room - it already fits neatly between the wall and the door of the airing cupboard (because I built it round the tank, in an alcove in the bedroom - any bigger and there wouldn't be room for the bed!).

Cheers,

Howard