House-Wide Second Ring with Isolation via Contactor

[Tim A]

Good evening,

This isn't technically a DIY post as I'm not suggesting I do this work myself, but I'm looking at the idea for a new-build/rewire that I'm due to be progressing...

I have seen (albeit only once or twice) properties that have essentially installed a second ring main throughout the house usually with green sockets that can be isolated with a single contactor/switch usually sited by the front door.

The the theory is that the sockets on the second ring would be used for things that don't need to be on 24/7 but do consume some standby current. For example, TVs, phone/laptop chargers, games consoles, that type of thing. When you leave home for the day, you flick the switch the the front door and power is cut to all these devices.

I was reminded that I'd seen this idea due to the recent news items around the cost of devices in standby (well over £100/year for the average house) and rising costs of electricity, and it seems like a smart solution. I'm also think it could be easily linked to a burglar alarm to switch automatically on set/unset for example.

However - there are some downsides - the majority of time you're powering a closed contactor which itself will draw current, plus many devices these days while drawing standby power may not like being powered up and down in this way. It's also clearly not something people commonly install (but maybe that's simply because housebuilders don't want to spend £ on the extra cabling).

I'd really welcome anyone's thoughts on the concept!?

 

[333rocky333]

However - there are some downsides - the majority of time you're powering a closed contactor!?

you can also get Normally Closed contactors

 

[AdrianUK]

I have done something similar in workshop spaces that I've built in the past - red sockets live 24/7 & white sockets which are switched via a switched near the door.


It doesnt have to be via a contavtor - a 45 DP 'shower' switch would do just fine.

A contactor is only going to use a few watts, maybe 10W or so, so 100 hrs per kwh of energy.

 

[JohnD]

don't need to be on 24/7 but do consume some standby current.

the cost of standby energy over a hundred years would be dwarfed by the cost of the solution you suggest.

 

[JohnW2]

I have done something similar in workshop spaces that I've built in the past - red sockets live 24/7 & white sockets which are switched via a switched near the door.

Indeed - similar here.

It doesnt have to be via a contavtor - a 45 DP 'shower' switch would do just fine.

True -although if the OP wants the switch by the front door, it might be a bit tedious (and greedy on cable) to actually wire the circuit via that route.

you can also get Normally Closed contactors

A contactor is only going to use a few watts, maybe 10W or so, so 100 hrs per kwh of energy.

I don't know whether such an animal exists 'off the shelf', but it would theoretically be possible to have a switch/contactor which was mechanically 'on' or 'off' (and remain in whatever state it was in) with switching between the two states trigged by a solenoid, which would only have to draw current for a second or two.

Kind Regards, John

 

[AdrianUK]

Indeed - similar here.
True -although if the OP wants the switch by the front door, it might be a bit tedious (and greedy on cable) to actually wire the circuit via that route.

I don't know whether such an animal exists 'off the shelf', but it would theoretically be possible to have a switch/contactor which was mechanically 'on' or 'off' (and remain in whatever state it was in) with switching between the two states trigged by a solenoid, which would only have to draw current for a second or two.

Kind Regards, John

I did mine as a variation on the 'lollipop' circuit - 6mm^2 from the OCPD to the switch & the two legs of the 2.5mm^2 ring leaving the switch terminals.

I'm sure you can get a mechanically latched contactor - one 'pulse' to latch it ON & a second to release the latch. The coil consuming no power otherwise.

 

[JohnW2]

I'm sure you can get a mechanically latched contactor - one 'pulse' to latch it ON & a second to release the latch. The coil consuming no power otherwise.

As I said, it's obviously theoretically possible, but I don't know how readily available such animals are. They obviously would not be safe for 'isolation', biut would work fine for the functional switching the OP wants - a separate (conventional) 'isolator' for the circuit would be desirable.

Kind Regards, John

 

[333rocky333]

I was meaning CT contactors, they come N/C N/O or even a mixture of both
Similar to this, rather than a clunky old school contactor

 

[JohnW2]

I was meaning CT contactors, they come N/C N/O or even a mixture of both
Similar to this, rather than a clunky old school contactor...

Fair enough - but none of those like your picture that I've seen are 'latching' - so, according to whether the contacts are N/O or N/C, their coil will be drawing current continuously either when the contacts are open or when they are closed - whereas, as I said, if a latching one can be found, it would only draw current for a second or two each time the state was changed.

Kind Regards, John

 

[FrodoOne]

In lieu of additional "House" wiring, have you considered using "Wireless Remote-Control Socket" devices, such as any of those pictured in https://picclick.co.uk/Remote-Control-Socket-Wireless-Switch-Socket-Uk-Plug-333411761621.html ?
Each "device" can be programmed to an individual "control signal", groups of devices can be programmed to respond to the same signal or all could be controlled with one signal.
(However. if the devices are a long way apart, the signal from any particular location may not be received at one or more other locations with sufficient "strength" to operate some devices..)

 

[winston1]

In lieu of additional "House" wiring, have you considered using "Wireless Remote-Control Socket" devices, such as any of those pictured in https://picclick.co.uk/Remote-Control-Socket-Wireless-Switch-Socket-Uk-Plug-333411761621.html ?
Each "device" can be programmed to an individual "control signal", groups of devices can be programmed to respond to the same signal or all could be controlled with one signal.
(However. if the devices are a long way apart, the signal from any particular location may not be received at one or more other locations with sufficient "strength" to operate some devices..)

Those devices are effectively on standby 24/7 themselves. How much power do they take compared with say a modern TV on standby?

 

[ericmark]

I have seen many houses with a contactor which switches a outlet in every room on/off, it was called economy 7. The question is how long can items be switched off for before it causes a problem, I use "Smart" bulbs, in the main to dim them, but had a problem in my bedroom as also used "Smart" switches, and there was not enough load on the circuit for the "Smart" switch so one bulb swapped for a standard one.

Some weeks latter came to use the bulb in another room, and found no longer connected to zigbee. So that bulb needs re-entering on the system.

So how long can items with stand-by be switched off before it causes problems in that they need re-programming? With the exception of Sky, it seems the rules are stand-by must only use 1 watt. And using my energy meter many items on stand-by don't register as using any power, clearly must use some, but my PC for example has a button cell which lasts for years and years to keep the memory active.

I see the point in two ring finals, so essential on one and non essential on the other and a stand-by power supply for essentials, so they can be battery or generator powered when we loose grid power, but I question if turning off items on stand-by would work, or just cause problems, I know my cooker needs re-setting if it looses power, and until clock set will not work, but microwave will work OK without setting the clock.

I have a weather centre which works on a AA cell for around a year so it seems to power a clock and receive auto wireless time correction does not need massive power. All my TRV heads use a pair of AA cells, again not only a clock but also a motor, last around 2 years.

It is easy to say 1 watt = 8.76 kWh per year so switching all the 1 watt devices off can save a lot, but it is a maximum of 1 watt, what do they really take, I have used 800 mAh AA cells in my weather station, which last around 6 months, to be fair only last 8 months without being used, so looking at less than 1.8 watt/hour per year.

 

[JohnW2]

In lieu of additional "House" wiring, have you considered using "Wireless Remote-Control Socket" devices, such as any of those pictured in ...

Those devices are effectively on standby 24/7 themselves. How much power do they take compared with say a modern TV on standby?

As winston says, to attempt to save 'standby energy usage' by using devices which themselves use standby energy is an iffy concept, not likely to save much, if any, energy usage.

However, I assume that this is about saving cost, not energy, and, particularly now that standby usage is generally getting very low, any approach which involves capital outlay (a handful of 'remote sockets', or cabling/sockets/contactors per the OP's proposal) is likely to leave one 'out of pocket' for years or decades, maybe an entire lifetime.

There is also the possibility that, for some equipment, repeatedly removing and the re-instating their power supply (rather than leaving them on standby) may reduce lifetime of the equipment and thereby have potentially major long-term financial implications (electronic devices very often fail on 'power-up').

Far better to reduce by a few seconds the duration of one's electric showers, or reduce by a few mL the amount of water boiled in a kettle etc. etc.. That will result in immediate savings (probably comparable with those being discussed here, which come at significant cost), with no capital outlay and no other financial downsides.

Kind Regards, John

 

[davelx]

Fair enough - but none of those like your picture that I've seen are 'latching' - so, according to whether the contacts are N/O or N/C, their coil will be drawing current continuously either when the contacts are open or when they are closed - whereas, as I said, if a latching one can be found, it would only draw current for a second or two each time the state was changed.

Kind Regards, John

There are plenty of bistable contactors available, which only draw power as they are switched. Used with a SPTD/centre-off retractive switch these would do the job. Not cheap - >£50 for the contactor and then you need the enclosure etc.

 

[ebee]

Interesting idea. I think each installation would need to be considered on its own merits re costs, savings, use etc etc so no one answer to all (or the majority of) all installations