What can I use to switch from mains to generator ?

bloodnok

Not sure if I'm on the right board but an uncle of mine has a workshop with a couple of lathes, heater, and other woodworking equipment ( All 240v single phase ) all working off mains electricity, but where he is in Mid Wales his electricity supply is quite often interupted, usually in the middle of something he's making.
He's now bought a diesel generator and asked me if there was a simple switch that could be fitted so that if his electricity failed, he could just press a button or throw a switch to instantly disconnect the mains and connect the generator.
Hope I've explained what's required............One switch with a mains and generator feed and one outlet to his equipement..... switchable.
You were the only brainboxes I could think of asking !
Thanks

bookduck

Computers would use a ups. For larger currents and longer times, these are very expensive as in tens of thousands of pounds upward. The big giveaway is heaters - to power these you will need lots of current.

The big problem is synchronization of phase and best zero degree crossover switching, but I'm not sure what he means by 'instantly'.
*******
An electrician should easily be able to do this.

There are relays that will drop out, so that should the power fails, it switches over to a separate source of power.

The best way is to get the generator to auto start on power loss - done internallt by the gen or, another relay (the generator does start via a battery??). So you have 2*240v inputs - one from mains and the second from a generator. If the mains fails, another relay switches to the second source of power. There will be an interruption for the generator to start and you might need a time delay before the generator output is put onto the mains - a capacitor circuit probably will do, or the generator may have a circuit to already do this.

You would also have to factor in what to do when the electricity is restored again as you do not want it automatically switching back straight away.

*****
if you want an uninteruptable service, then it gets expensive. Instead of powering your items you need the input to charge batteries, while charging batteries, the power also powers a dc (battery power) to ac generator (could use an inverter circuit instead).

unrich

The time I came across this kind of thing was when I was using/experimenting with solar power.

Google "homebrew windpower relay". "generator relay".

A relay is a switch controlled by electricity. So you could have it powered by the mains and when powered it sends mains electricity through to the workshop. When the mains fails the switch drops, the generator starts up and the workshop gets powered by the genny. I'm assuming the generator has an external startup switch?

Fusing and earthing may be an issue.

Also the relays I have used have had a max amperage of 10A at low voltage. Less lethal than 240V and 10A.

bloodnok

He'd be happy with a manual switch that he could flip over just to completely isolate from the mains, and then start the genny..............Bog standard, nothing high tech.
Yes the genny starts on the button
Thanks for your replies

Spire128

Hi

Well the one way it could be done is by breaking the connection between your electricity meter and you own fuse board, then insert an Double pole change over switch, with the common end of the switch to your fuse board and the other connections to the mains incomming supply and the gennerator.

If you as using this on a std domestic supply then the switch will need to have a minimum rating of 100amps and capable of switching the circuit on load.

I provide the above information as is and would advise that you consult a suitable qualified person to examine your installation and make recommendations. This is not a job for Diy u need to get an electrician to install it.

isofa

Does he have a single "in" point for the supply into the workshop, and can this be easily isolated from the mains supply to the house? (i.e. does it run off from the main house "in" point on your RCD board?)

If so, for a manual solution, where the main power comes into the workshop (before it gets distributed to the sockets/equipment) then a double pole switch is needed to simply cut the supply off to the workshop switching it to the generator output. You'll need to make sure it is highly rated as per Spire128s advice above.

The switch would essentially switch the supply to the workshop from the mains to the generator, so even if the mains comes back on, it would be isolated from the workshop, until the switch was flipped again (and then the generator would be isolated).

But only do this is you can isolate the workshop and work on the supply safely, and if in any doubt at all, get in an expert!

Spire128

isofa wrote: »

If so, for a manual solution, where the main power comes into the workshop (before it gets distributed to the sockets/equipment) then a double pole switch is needed to simply cut the supply off to the workshop switching it to the generator output. You'll need to make sure it is highly rated as per Spire128s advice above.

I would use a change over switch, the reason is that it will ensure that only the Generator or the Mains supply is connected at any one time, as if the generator output is not synced to the mains supply if they were both connected something would have to give, and it would mostly be your generator and or the wiring.

isofa

Yeah good point, I should have made that clear, you don't want things fusing!

Zahc

http://www.gencontrol.co.uk/AMF%20control.html

Just a thought

Zahc

Phil_L_2

In this case I would recommend the simple changeover switch. Make sure that it switches all conductors except the earth. The alternative would be a changeover contactor driven by the generator arranged so that when the generator started the contactor pulls in disconnecting the mains from the load and connecting the generator. Enbray produce some good units which you may be able to pick up in an industrial scrapyard.

Remember that the electricity company REQUIRE a physical break between their supply and any private generators so make sure that you have a break before make arrangement.

Fried Linesmen=Big Trouble

isofa

I found this on a search which might be an ideal switch to use, the page also has some good information answering pretty much your original question: http://www.justgenerators.co.uk/pages/powertransfer.htm