Switching between two separate 13A circuits

[Rick Bowlby]

I would be grateful if someone could provide some electrical advice.

We have Economy 7 / dual rate electricity meter, and have installed a separate 'night rate' circuit to connect a storage heater and immersion heater without the need for a timer (in any case only 5 of the 7 hours are fixed, the timing of the other 2 are at the discretion of the supplier).

We have a spin dryer and often run that in the middle of the night as well to use the cheap rate - but this is achieved by plugging a timer into the 24hr (ie normal) mains circuit. This can be unreliable - the timer has to be reset each time it's unplugged, and anyway the night rate timings vary as I mentioned. What I'd like to do is eliminate this timer. I've thought of 2 possibilities:

1) Add a socket outlet to the 'night rate' circuit, adjacent to the dryer (and give it a red cover plate or something to make it stand out). Then you simply plug the dryer into whichever circuit you want to use.

2) If there is such a thing, fit a 'circuit switch' unit which can switch between the two different circuits, and which feeds a single socket outlet for the dryer (which stays permanently plugged into it).

The big advantage of (2) for us is that a switch can be installed above a worktop, with the socket outlet below. With (1), I would need to bring the plug through the worktop to be able to move it between the two outlets, which would be messy.

Is there a switch unit which can switch between 2 completely separate circuits - ie taking L1, N1, L2, N2 as input and LO, NO as output, will switch between (L1-LO + N1-NO) and (L2-LO + N2-NO)?

Hope this make sense!

Thanks for any advice.

[dom]

I can see that sometimes you want to run the spin drier in the day, and sometimes take advantage of night tariffs.

But surely the timer is indispensible -currently you use the timer to both start and stop the machine?

If the machine has an internal electronic timer - it can't be programmed until it's powered - if mechanical it will just run down before it's powered.

You're also gong to run the machine for a lot less than 5 hours, so a timer can be set to the core 5 hours available.

How about a built in timer like this? (I use one on my immersion for economy 7)

[meow2222]

what you want is a 2 pole 2 way switch. The other option is a 2 pole 2 way relay, which would automatically switch to the E7 circuit when it was live, and back to the other feed at other times.

NT

[Owain]

You need a DP changeover switch. I thought MK made one as part of their Gridswitch range but I can't find it online.

Owain

[Rick Bowlby]

I need the switch rather than the relay. Any idea where I get one? I can't find such a thing on the MK website.

Thanks

[Rick Bowlby]

Thanks for the info. Can you suggest another manufacturer? Crabtree don't seem to make one either

[Rob Morley]

That was going to be my suggestion :-) In fact it would make sense to run the freezer from this too, and maybe some other stuff.

[meow2222]

a dp changeover is a 2 pole 2 way with 2 connections added, either is fine. I dont know any white plastic ones, but 2 pole 2 ways are a standard common item in toggle or rocker format.

If you're determined to have a white plate type, it would be easy to mod a twin lightswitch by screwing the 2 rockers together with a screw that goes thru the side of the rocker, so is not visible. Would mean dismantling it. Someone must sell them as ready made white plates though.

Another option is a white blanking plate with toggle or rocker switch fitted.

NT

[Rick Bowlby]

Thanks for your help, but I can't find anything described as a DP 2 way switch, only DP 1-way or SP 2-way. If they are a common item I must be looking for them in the wrong places. I'm not at all determined to have white plastic, anything will do as long as it looks tidy, but I'd rather not try and make it myself!

[Owain]

Given that all consumption during the off-peak period is charged at the cheap rate, it's really not necessary to run the freezer etc on a special or changeover circuit.

As the OP's tumble dryer is going to have a dedicated circuit from the off-peak CU anyway, it might make sense to do the changeover in the 'meter cupboard' which would allow a more industrial type of switch to be used eg

clear labelling at the tumble dryer that the circuit is dual fed would be advisable.

Owain

[Dave Plowman (News)]

I've never seen a domestic type switch that would do. And I'm not sure how easy it would be to find a 20 amp DPDT rocker that you could fit to a plate - they're usually 10 amp max.

[Rick Bowlby]

Thanks for the link. I think this may be the sort of thing I should be looking for, although it seems a bit heavy duty. There may be somewhere nearby I can hide it.

Thanks for your help.

[Rick Bowlby]

Is this the kind of thing you mean?

so, what do they mount into? They look as if they require soldered connections.

[Dave Plowman (News)]

They clip into a rectangular hole - needs to be fairly accurately made, though.

They take car type 1/4" spade connectors. These can be soldered or crimped to the cables.

[meow2222]

google dpdt switch

any electronic component supplier will have them. RS components, rapid electronics, etc.

Toggle switches mount in a small round hole, maybe half inch or so. Rockers mount in a big square hole, which would not be easy to make in a brittle blanking plate. Toggles will need soldering to, rockers use push on crimp connecters.

I'd go for the modified white mains switch meself, its less hassle than the other 2 if you cant solder. It also will look just like any other household switch. Theyre cheap and not very complex to reassemble. That or a single switch and dpdt relay.

I'm not going to mention homemade knife switches :) That would have been the solution a century ago.

NT

[David Hansen]

On Sun, 14 May 2006 10:35:14 +0100 someone who may be Rick Bowlby wrote this:-

1) Why unplug it?

2) Battery backed electronic timers are available.

Personally I would stick to running it in the fixed five hours, unless looking for some sort of engineering challenge.

[Christian McArdle]

It would be bad to combine two circuits in this way. It provides two points of isolation to one circuit. A fault could backfeed the two circuits, too.

If this must be done, I'd run the machine only off the always on circuit. You could stick a relay on this, provided the relay coil was fed via a suitably isolated means from the timed circuit (such as an optoisolator). A switch would then be used to determine if power should be available during peak times. The switch would probably just short out the relay output terminals to provide power even when the timed circuit was off. This way the circuits are kept apart.

Christian.

[meow2222]

not sure I understand what you mean there.

NT

[Rick Bowlby]

I've come to the conclusion that you're right. Simple domestic wiring is well within my grasp, but I can't face building my own components right now. I'll keep it simple.

Thank you everyone for your responses. I've learned something anyway!