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Whilst pondering my navel in the bath, and reviewing the probable/inevitable electricity cuts in the future due capacity and adverse weather, I wondered how I could power my (gas) central heating pump, controller and a few lights in order to stay reasonably comfortable in the event.

Generator says my brain.

OK, don't really want the genny running in the kitchen, so an outbuilding would be ideal - and plug it into a 13A socket.......?

So, here's the question. My distribution board has 3 MCB lighting circuits and several RCD Power circuits. I guess to avoid buggering up the grid I would need to switch off the board master, and unneeded circuits. Then, keep the load below 13A and......................?

Will the genny output feed back into the board OK and then power the remaining loads? How does an RCD cope with reverse current?

Now where was that soap.......?

You certainly need to switch off the master, a very important point, it could be lethal to the sparky trying to fix the fault on the network.
My solar feeds into the house via an MCB in the garage, a switch in that consumer unit (the garage circuits are on RCBOs) and then to the house main consumer unit via a 100 mA, time-delayed RCD. (The 100 mA is a requirement of the solar setup, I guess a standard 30 mA would be OK for a genny) The time delay is for discrimination in normal use. There seem to be no problems with feeding the RCD backwards.

For emergency use I am proposing to install a small consumer unit (6 final circuits)to feed the important circuits - freezers, internet router and a few scattered sockets for table lamps, TV etc. My emergency supply comes from the solar battery and has 2.5 kW capacity. The small consumer unit will be fed from the normal supply (mains or solar if its generating) most of the time and switch to the emergency supply when needed, thus leaving all the main house and garage circuits still connected to the utility supply, no need to remember to turn off any other RCDs/MCBs. I will have to install a "proper" earth for this as I am on a PME (aka TNC-S) connection from the utility.

Thanks for that - I would prefer a genny to solar, of course, in case the power goes off at night . How long would 2.5kw run your system for?

Really that is a 'proper' system.

For a modest requirement such as a couple of lights and energising a couple of lamps a small genny, say 650w, would be more than adequate. You could avoid the grid problem by 'creating' a totally separate circuit. For instance run an extension lead from the genny and plug the lamps in to that. The downside is it is not automatic.
Central heating control is more difficult. Our previous home was a plug and socket system so I could simply unplug and plug into the genny.
Our present home is hard wired. If you put a plug and socket in the system then you could simply plug it into the genny.

To answer the 2.5kW battery question, LED lamps could be run fir days. The real drain would be the CH pump.

"the CH pump." is the main point of it - I'm not bothered about a few lights.

Boac wrote: ↑

Sun Nov 28, 2021 5:35 pm

"the CH pump." is the main point of it - I'm not bothered about a few lights.

So if you can plug the CH into the genny then that will do the trick.
An alternative might be a deep cycle battery as used in a caravan. Connect a suitable 12v invertor to produce AC. I have an invertor that can produce about 140w that I used to use to power a laptop.
A 50AHr battery should be able to a CH pump for sometime.

Following on with PNs simple solution, wire the pump to a socket so that normally it runs from the mains. Install a second adjacent socket that will be connected to the generator. At the time of a power cut, simply start the genny, and change the plug to the second socket. Of course you might want to wire the boiler and pump together as there's not much good in the pump running if the boiler is cold due to a lack of sparky bits in its own wires.

There are many ways to make this rather more automatic but that could well be beyond your needs and wishes.

Keep warm....

Second power supply is a daunting task! Hence my navel gazing. It would seem a far more preferable solution if it works, and I would be able to route power to other MCBs as needed subject to genny capacity?

I stayed in a house in India, definitely wired by an Indian. He had a magnificent chandelier over a sweeping marble staircase rising to a large galleried landing.
He also had CFL lamps hanging from simple wires from the ceiling and bank of truck batteries under a bench in his downstairs room, I hesitate to describe it as a lounge. The bench looked like something knock up from pallets.
When the mains failed, which happened regularly over 3 days, the CFLs started immediately.

How much effort you put in to depends on your risk/needs assessment. Our previous home had a log burner and candles.

If you are so keen, then install (or have installed by that competent person) two separate consumer units, one to feed the generator items and one to feed the rest of the house.

The regular supply feeds the rest-of-the-house direct as at present but is connected to the generator-only consumer unit via a mains/generator switch which is a high current two pole changeover switch (see google for much information).

When the mains fails, the switch is manually changed connecting the generator to this consumer unit and very importantly, thereby absolutely isolating your generator circuit from the mains. In this way there can never be any inappropriate connection between the two systems.

Assuming that you are in the UK it would be prudent to remain on the right side of the current(!) wiring regulations. Actually, wherever you are, it would be sensible to do that...

All wonderful plans, but not do-able here. If I go this route, treating it like unifoxos's solar input, then I gather my proposal would work - and do the job. To repeat - a separate wiring solution is not in scope. I need to see what the current draw of the CH pump is.

The plug and socket solution is the least expensive. If the current drain is low, your CH requirement is limited, (say 6 hours per day for example), and your expected outage is measured in hours and no more than a day, a battery and inverter might be the least expensive.

Your generator might be a couple of hundred, then there is the question of fuel, noise and ventilation......

Yes, battery and inverter on the menu, but I need to assess current load, and of course the temptation with more amps is to power more!

Boac wrote: ↑

Sun Nov 28, 2021 9:21 pm

Yes, battery and inverter on the menu, but I need to assess current load, and of course the temptation with more amps is to power more!

Don't think of it as amps, think of it as run-time. If you've got a 12V 12AH battery then you can supply 12W for 1 hour, or 1W for 12 hours. Scale as appropriate for mains-powered loads.

To clarify, my inverter has a capacity of supplying 2.5 kW of leccy. The battery is 8.2 kWh. In tests last month I fully charged the battery from supply in the afternoons, and set it to provide power from 1730. Depending on what I was cooking for dinner (gas hob, 1kW microwave, 2.3 kW oven) the battery would last until about 2100 - 2300. Of course, if I was using the oven and the microwave at the same time, the supply would be augmented from the grid. I was not using heating at that time.

My house takes about 600-800 Watts of "background" power for stuff on standby, fridge, freezers, internet router and file servers before I start using any for my daily purposes.

One could install a battery and inverter without solar panels, of course, charge it up at economy 7 rate during the night, and use it when you would be paying normal rate in the daytime. I wil be setting this up when the supply situation is clearer - my previous supplier ceased trading and i have been switched on to a fresh one.

My house takes about 600-800 Watts of "background" power for stuff on standby, fridge, freezers, internet router and file servers before I start using any for my daily purposes.

Actually that brings to mind a use for a Smart Meter.
Every morning, around 7am, my daily demand so far is 2kW. Over 7 hours this equates to an hourly demand of abot 300w. As we have an electric towel rail at 80w it follows all the niff naff and trivia is burning 220w. I imagine the fridge/freezer takes the bulk of that.

My gas consumption is just hot water and UFH. The usage still 7am is always 750w or 10w/hr. Expensive pilot light!

llondel wrote:Don't think of it as amps

Old habits die hard (W=V x I?)

We have a rather cumbersome backup system. Two systems, actually.

By law the PV array and the wonky wind turbine and the V1.0 Tesla Powerwall isolate instantly in the event of a powercut. The newer second system isolates from the public main but continues to power the central heating circulation pump and the heat well pump or he self-stoking boiler as well as powering LCD lighting and 'puter UPS. The Powerwall V2.0 is normally topped up by either the wind or solar and works best when you don't need it. In this weather, for example, neither wind nor solar is producing a single wiggly.

Being Tesla it was bloody expensive to install. The whole shebang, including Back-up Gateway, cost a little over £7k, but is very reassuring to have. We no longer have as many powercuts as we used to. It was quite normal to have a dozen or more per year, but now we're down to two or three at most. The last one was in April. They tend to be for less than an hour.

The Powerwall 2 stores about 13kWhr and can deliver up to 4kW which is more than enough to power the log-feeder boiler and the heatpump and CH systems all at once.

One thing I will say about a woodchip boiler though: BEWARE! woodchips emit quite large amounts of carbon monoxide when stored in an enclosed space. I've had six CO detectors/alarms fitted in the storage area and have copious ventilation to dump the CO outside. Plenty of people have been killed by CO poisoning from woodchips and it's something which receives surprisingly little publicity.

Boac wrote: ↑

Mon Nov 29, 2021 8:04 am

llondel wrote:Don't think of it as amps

Old habits die hard (W=V x I?)

I mean sizing it to last a while rather than for maximum output. Commercial computer UPS boxes tend to be designed to supply rated load for about 5 minutes, to give stuff a chance to shut down cleanly. I have a box capable of 1kW or so on about 16% load, so it'll survive around 30 minutes before deciding to shut down. It is possible to get systems that allow external battery packs to be added to improve runtime but they also cost quite a bit more.

I mean sizing it to last a while rather than for maximum output.

We are on the same hymn sheet here - it's just that I start with Amps and arrive at KWH via volts and the clock.

Out of interest, what sort of cost for a decent battery and 240V inverter?