Mains changeover switch to generator backup

David · 2021-12-03T20:51:43+00:00

Prompted by the power cut thread.As far as I can tell if you want to be able to power your home from a generator if the mains power goes off then you need a changeover switch to isolate the mains before you fire up the generator.A quick and nasty search of Amazon suggests that these may not be very expensive - perhaps around £100.You would presumably then need an approved installation to provide a feed in from the generator and a guaranteed isolation from the mains.I assume a competent electrician could do this.Any feeling for the cost of this installation?Dodgy calculation suggests that a 60A mains feed would require roughly 13 kW of generator power to maintain supply, but I am assuming that this would not be the aim.Target to be able to run the fridge and freezer, lights, and central heating pump and controls.Electric fires, electric cookers etc. not catered for.If power is out then the internet is presumably out as well, and probably mobile phones, so basic amenities only required.CheersDave R

Dec 03, 2021 Last reply: 4 years ago 24 Replies

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Mike Humphrey 4 years ago

The regs say it is. After all, the power cut could be caused by the cable being cut just outside your house, which would cut the earth as well. Or even the cable being deliberately removed (to replace it, for example).

The setup I described had one circuit fed from the generator not passing through the CU. In this case you would need another RCD (or RCBO). If the generator supply passes through the CU RCD, then you don't need to add another one. But you do need RCD protection on every circuit, as your generator is TT earthing - if your CU only has RCDs on some circuits, you either need to add more RCDs/RCBOs or put a time delay RCD in front of it.

Yes, that's the downside of putting everything behind the changeover switch - you can't see when the power comes back.

Mike

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John J 4 years ago

Perhaps worth mentioning the input DC current (ignoring efficiency/losses) of a 12 supply from a battery will be around 20 times greater than that delivered to a 240 volt load - not something a typical battery will sustain for long. Hence my preference for a generator.

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tony sayer 4 years ago

I've been told that the transmitters at Emley Moor are on f*ck off size UPS units to keep on air whilst the gennies start up!...

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ARW 4 years ago

So are the essential circuits at Doncaster Royal Infirmary.

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ARW 4 years ago

My Dad would fork out for a 7/8kW genny with electric start and a changeover switch tomorrow. The inverter was all my Mum would allow him to have and she was not happy about that. She cannot see the need.

Your point about DC losses and the battery not lasting very long are noted. Thank you.

However my parents have two cars sat in the garage next to the inverter that they can use top up power up if needed. It was never a 24/7 solution but it could run the CH for a few hours a couple of times a day and keep a couple of table lamps on for several hours before they needed to top up. As they are not in rural Aberdeenshire hopefully they will never go 3 days without electricity.

For some reason your post has reminded me that I am going to have to get laminated instructions how to use the inverter printed off for them or for a neighbour to be able to do it for them. My Dad is getting a little forgetful and my Mum has no interest in it.

Cheers

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