Re: Generator standby wiring question (again)

[Dave Liquorice]

No. If you fire the genny up and plug something in is it unsafe? Depends...

> It's the same as powering a few small items in the house throught > the existing wiring.

Except that without N bonded to E and L E fault will not cause any fault current to flow (think about it there is no circuit...) but will raise the N way above E, probably up to the full generator output voltage. Bear in mind that most switches and MCBs are single pole in L then things "switched off" aren't. Also as N and E are quite likely to be interconnected somewhere the installations E could also rise to the full generator output voltage.

One end of the generators winding needs to be bonded to the frame of the generator and to local earth and to the main earth terminal of the installation. It is the bonding of local earth to the main earth terminal and thus the suppliers earth that can be problematical with some types of installation.

For extra safety you could install an earth spike and connect it to > the generators earth terminal, that's about all you'll need to do.

Assuming that the gennys earth terminal also bonds to one of the generators phases.

[Lurch]

On Mon, 05 Apr 2004 00:22:16 +0100 (BST), in uk.d-i-y "Dave Liquorice" strung together this:

That would also apply to anything plugged directly into the genny. It'd be no more 'unsafe' than just plugging something in to an extension lead on the genny.

Where would they be connected?

That is why when using a gennerator you should isolate the suppliers earthing facility with a link, or just unscrew it, and turn opff the main switch of the CU or use a changeover switch.

I seem to think that most are.

[Dave Liquorice]

Not quite, a single appliance on a extension with a L E fault will only mean that that appliances N and/or E rise above true E. In an installation the *whole* installations N and/or E rises. In the case of E rising all the back boxes and fitting screws of the sockets etc or exposed earthed metal work on any connected appliance or E bonded fittings (CH pipe work, taps etc) all becomes a shock hazard...

A raised N shouldn't be so much of hazard but could still present a "surprise".

I hedged that statement a bit. B-) With proper DP break before make change over switch there shouldn't be a N E connection, other than the one intended at the generator.

Personally I'd get the type of supply changed such that the suppliers earth can remain connected or fit a 3P switch. Having to to a manual disconnect/connect the earth is just asking for it to be left in the wrong state at some point.

"think"! I'd make damn sure it was, no assumptions or "thinking".

[Lurch]

On Tue, 06 Apr 2004 17:26:20 +0100 (BST), in uk.d-i-y "Dave Liquorice" strung together this:

So pretty much a 'check what you're doing as different installations will require different solutions' sort of answer.

Are you suggesting fitting a switch to the earth? I do hope not, it's a serious contravention of BS7671. What if the switch was to go faulty on the earth pole alone?

Quite, hence the first line of my reply.

[Dave Liquorice]

Yep. B-)

Same as "forgetting" to adjust the manual link or dis/reconnect it that you where suggesting, even if the latter obeys the regs I feel it is rather to prone to Sods Law.

To detect a naff switch, wire a neon across the poles. If the neon on the closed side glows you have a problem...

[Lurch]

On Tue, 06 Apr 2004 22:30:26 +0100 (BST), in uk.d-i-y "Dave Liquorice" strung together this:

But human error can knacker any good theory, if someone were to 'forget' to switch off the CU then disastrous consequences could occur when the genny was fired up. A faulty switch is beyond human control.

I think we're in bodging territory now. If you want to fit a switch to the main earth then go ahead, I would strongly advise against it and would never do it myself though.