Correct me if I'm wrong - please. Emergency generator question

[NotMe]

We moved to a remote-ish part of Scotland last year (yes, some people have all the luck) and we asked our nearest neighbour if it was worth getting a generator. "Not worth it he said" and last Jan we had a day without power and the local village was out for 3 days. Yesterday we had an 8 hour outage and are expecting similar if tonight's weather forecast is correct.

So, to get to the point. I have been lent a small (2.2KVA) generator and am hoping to use it for the lights and aged aunt's electric blanket and on-suite macerator.

Here are my assumptions:

1. If I isolate the circuit that these devices are on (yes they are ALL on the same one! - rewiring is a next year job) by swiching out its MCB then no power will get from the genny to the busbar in the fusebox.

1. If (1) is correct then I can leave the rest of the circuits connected to the incomer so I'll know when the power comes back on.

Do I have to do anything with the neutral - if so I'm buggered as I have no idea which neutral belongs to that circuit.

Also, I read somewhere that I should tie the neutral to the earth in the plug conneted to the genny (something about floating earth that bemused me). Is this true or wise?

If the above is OK I will buy a decent size genny (a properly regulated one) and extend the idea to include the fridge etc.

Hope you can help - the winds getting up!

Ken

[Harry Bloomfield]

[e-mail] presented the following explanation :

To do that would be illegal and you might well face manslaughter charges should there be an accident as a result. All it takes is someone to come along and reset the MCB, or the MCB to be faulty and your generator will be feeding directly into the mains. Anyone working on the mains supply lines due to fault might assume he/she were safe to do so, but there you are with your generator connected.

There are ways of achieveing the interlocked switching, but they are too expensive/complex for home users.

The only safe way is to provide a completely separate ciruit from the generator - perhaps an extension into which you plug your appliances after unplugging them from a normal mains socket.

[Chris Hodges]

Can't you still get a serious break-before-make manual changeover switch then?

[meow2222]

Its a bodge I wouldnt want to do, and it could make the genny case live (mains comes back on, polarity wrong somewhere or broken neutral). Also as explained its too much of a risk of manslaughter to be anything but criminal.

Doing it safely is easy enough though. The cable coming from the fusebox/CU that feeds your lighting circuit should be interrupted, and a switch (or better a relay/contactor) put in so you can switch it betewen gen and mains. Its important to switch both poles, L&N. If you use a relay, mains power causes the relay to switch theload to mains, no mains power and it switches to the gen setting. It may also be a good idea to check the removed lighting feed is not still connected via a borrowed neutral. Or live even, I've seen that happen.

If you just want a quick get it going job, take the lighting feed cable out from the CU and hook it to the gen, but dont connect the gen into the fusebox. If its a 5A/6A/10A circuit I expect one could put it on a

13A plug, but I've not seen that done and dont know what IEEEEE would say about it.

Portable gens typically dont have anything like the safety features of fixed mains supplies. As it stands you'll have no rcd, sometimes no mcb, and often no earth. A plugin rcd on the gen is a good idea, as is some kind of earth, though those tend to wait until you make it more of a regular thing. Also best not to use computers etc on a small inductive generator, unless you appreciate the problem and always use the right loads and plug/unplug in the right order.

TBH gaslights are easier, cheaper and far more reliable. But they dont keep the freezer cold.

NT

[Harry Bloomfield]

[e-mail] expressed precisely :

No you can't, or at least not safely and legally. The system would need to be absolutely fail safe and mechanically interlocked. Relays, or more correctly contactors are known to sometimes weld up their contacts.

...and what happens if someone subsequantly alters the sub-circuit, borrwing a nuetral or back feeding from another circuit?

What ever is installed has to be completley fool proof, no matter how good the fool is.

[Andrew Gabriel]

Also note that you are not permitted to assume the supplier's earth connection is still working during a power outage, i.e. unless you are already on a TT system (your own earth rod), you will have to provide your own earthing for when operating the generator.

[Guy King]

The message from Harry Bloomfield contains these words:

Nah - someone will just invent a better fool.

[The Natural Philosopher]

OTOH if iu are so far away from civilisation, no one will notice, and if you try feeding teh whole local mains with a genny, all that will happen is that it will stumble to a stop trying to light up the neighborhood.

Itsd convention that linesmen strap all the wires together anyway.

[Newshound]

A big manual two pole changeover switch should be OK though. One of our local farmers has a livery yard and a couple of business units has such a switch by his main board next to a socket where he can plug in a genny. They are not cheap, though, at 60 or 100 amp rating. If they were more reasonable, I would probably put one in myself.

[David Hansen]

On Thu, 21 Sep 2006 18:21:50 +0100 someone who may be [e-mail] wrote this:-

It is rather too late to ask now.

The answer is that none of the things you have suggested are sensible or legal.

In a domestic setting the easiest short term way to do this is to have some emergency lights wired up separately to the generator. If it is really necessary a socket fed from the generator for the electric blanket. Note what others have said about safety though. The en-suite macerator can be ignored during the power cut, just use the gravity fittings.

If you want to do this more permanently then get a suitably qualified electrical engineer to design a system that will be safe and legal.

[Bill]

In message , Harry Bloomfield writes

£185:00 too expensive???? the incoming mains to two consumer units and have the transfer panel wired into one of them so that you have maintained and non maintained consumer units.

Or as my uncle did 40 years ago have a lead with a 13A plug on each end and put one end to the genny and the other into any socket in the house and away you go!!!!!!!!!!!! (Not a serious suggestion but he did do it and lived!)

>

[The Natural Philosopher]

Yup. Thats probably what I would do to, in an emergency, knowing that the house is earthed, and if the main trip was switched on, and somebody connected that lot to a dead mains, the genny fuse would blow, due to its whole output being shorted by most of west suffolk, and if they connected it to live mains, the genny fuse would blow, due to it being connected to the grid at a random phase and frequency.

[Newshound]

Very neat, ISTR the changeover switches are over £100

[Newshound]

This is real scary though

[meow2222]

fairy nuff.

There is no such a thing as a system that will stay safe if someone comes along and modifies it unsafely.

NT

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Newshound" saying something like:

What's scary about it? It's for a 10A load - all you feed with it is a sub-main box carrying vital circuits. Lighting, telly, PC.

[Stephen Dawson]

Linesmen do not strap all th wire together, if they are on a low voltage line.

The only safe way to do this is to use a changeover switch.

[David Hansen]

On Thu, 21 Sep 2006 18:21:50 +0100 someone who may be [e-mail] wrote this:-

Assuming that you survived the night this is the way to do it properly.

1) split the wiring into vital and non-vital circuits. Wire each up to a separate board. 2) decide on your changeover strategy. In a large building this would be automatic shedding of the non-vital circuits and automatic startup of the generator upon external supply failure, with the generator connected to the vital circuits when it is up to speed. Return to external supply may or may not be automatic, there are advantages in doing this manually at a suitable time. All this may well not be desirable in a house, instead changeover would be manual with load shedding ideally interlocked with generator starting. 3) decide on your earthing strategy. Remember that the external earth cannot be relied upon. 4) do the work.

[Ian_m]

You don't actually need to switch the whole house electrics of course. A friend in New Forest with intermittant electric supply had a generator fitted that supplied just the boiler, fridge/freezer, kitchen lights and single socket for TV/Sky box. Uses a tiny Honda generator.

I think this was done with a feed from CU via a contactor (?) with generertor power to a small CU with a 16A (boiler, socket and fridge) and 6A (lights) radially wired to the items in the house. He was having major building work done at the time so cable running was not an issue. I think the function of the contactor was to isolate the incoming mains and connect the generator power when generator was started. All done by an electrician, I think also some pavement was dug up as well to provide and earth spike/connection. And a battery powered emergency light thing in the generator cupboard (outside) that comes on if the mains fails so that you are a*sing around in the dark trying to get the generator started.

Only needed it once since fitting, 3 years ago, but thats life.....

[meow2222]

More often that not this will be true, but some of the time it wont be. People are often careless, make mistakes, some of the wiring repair scenarios dont fit what you describe, switches do fail and so on. This is why its illegal.

NT