Generator and boiler lockout

[Richard Walker]

Hi

Few years ago I bought a 2kW petrol generator to keep the home running when the mains power failed. Used several times, no probs except that the CH boiler locked out when the generator was switched in. A reset and all worked fine.

Last week had another power cut but this time the CH boiler locked out after about 30 secs even after re-setting (several times). Everything else in the house works OK, including gas fired Rayburn cooker, which is just the same sort of technology as the boiler.

Any thoughts on what is upsetting the boiler? -it's a normal wall mounted balanced flue unit from Vaillant.

Thanks

-- Richard

[Jonathan Schneider]

I guess the generated mains has something wrong enough about it that the boiler doesn't like it.

Or some part of the system is on a circuit which is dead in a powercut so the boiler gives up.

Jon

[Ed Sirett]

What arrangements are used to switch over the suppies. What arrangements are used to earth the installation? A polarity problem is centre stage here, especially if the gas lights but then goes out after a few seconds.

[Richard Walker]

Thanks, Ed

The gennie is switched in with a dp change over switch which isolates house from grid supply then switches gennie power into house. Normally switch boiler off at its isolating switch before switching in gennie, then switch boiler on when gennie has settled down. House is earthed as normal, gennie chassis is connected to house earth but not separately earthed.

Supply from generator is clearly lumpier than mains - a discernible flicker to lights. Might this be the problem? And if so, I wonder why it used to work but doesn't now?

Cheers

-- Richard

[Sparks]

Generators are generally center tapped, so you end up with +115v on one phase and -115 on the other. This may cause a problem with your boiler. With the generator running and the grid supply off, what are the voltage measurements between...

L&N - L&E - N&E -

Sparks...

[Richard Walker]

Hmmm... Voltage between L&E and N&E is just 85v when no load, disconnected from the house wiring. Voltage between L&N is 240v. Thought I had a reasonable understanding of electricity, but this has me puzzled. Should I not connect the generator earth to the house earth?

-- Richard

[Andrew Mawson]

Rayburn

boiler.

earth?

Is this one of the 'inverter' generators where they don't control the engine speed, but put the output though an inverter to produce correct frequency and voltage ?

If so, and if meant for the american market, it couuld be centre earthed 115(L) - 0(E) - 115(N) possibly.

AWEM

[Dave Liquorice]

Off load the rather primative AVR in the alternator will be confused. I would be at all surprised at odd readings, load it up with a couple of hundred watts or so and see what happens.

No, when the power fails you cannot rely on any of the supply wires to be what it should be, live, neutral or earth. What you should do is bond the generator chassis to a local (good) earth spike, bond one of the generator phases to the chassis and thus the local earth creating a "neutral" and have an RCD at the generator and run extension cables to the kit you want to power and plug them in.

It gets very messy and has lots of implications if you want to use the house wiring direct. Back feeding the main supply *HAS* to be avoided at all costs, not even the remotest chance of it happening by forgetting to open a switch somewhere. I do have vauge memories that you do have a proper break before make change over switch though. If that is the case the the bonding described above should sort things out but the supply earth should not really be connected. Hence the RCD as the earth loop impedance via the local spike will probably be rather high.