Jon
wibbled on Sunday 28 February 2010 03:30

I. GENERATOR TRANSFER CIRCUIT

The service wire is 000. I'm not even going to attempt a contactor for
that. I'd have to wire it hot and there's too much risk.

Can you not get the supply made dead by requesting the supplier remove the
main fuse to your drop? I assume you have a main fuse (well, fuses)?

OK, I'm in England, but I went one better - I needed my line made dead for a
day to install a new breaker panel, so I tool the chance to add one of
these:

https://photos.dionic.net/v/public/b...80550.jpg.html

(Isolator switch, top right). It is actually the one that *some* electricity
suppliers fit, but not mine alas. Technically I'm not supposed to put it in
that box (belonging to the supplier) but I reached an friendly agreement
with the supply fitter.

At least now, I don't have to call them if I need to make my cables dead,
and lose power for the whole day (they pull the fuse in the morning, and
come back in the afternoon when they feel like). And they charge each
time...

All I'm going
to do is make a fail-safe circuit to protect the generator when the power
goes
back on. It's only a 10kw generator so I'm using 120vac coil contactor
with
contacts rated for 90amps. I'm going to use the spare wire from the house
to the barn to signal when the grid goes back on. That will open the
circuit and shut down the generator.

view in courier

service

120vac 120vac signal
o o o
| | |
o o------------*
\ main \ |
o o |
| | |
| house | |
| | |
| | |
| barn | (COIL)
--- --- | generator ignition
-/- N.C. -/- N.C.. | o
| | | |
o generator o | ---
--- --- N.O.
- |
gnd |
---
-
chassis

Is there a neutral there? I though you lot were 120-0-120 or does that vary?
Because you would want to isolate the neutral too. Also the use of the
utility earth (ground) is in question in the event of a power failure.

With all due respect, your proposal is *wrong* on many levels and I can't
believe I'm seeing this on an engineering forum. I don't know your codes,
though I'm fairly up on mine, but the basic tenants of good design are
pretty universal.

You need a break before make changeover device which will switch all lives
and the neutral at least, mechanically interlinked and with guaranteed
isolation (contact separation) of all conductors (probably including ground,
check the NEC). Note, other ways of achieving this could be to present key
circuits (eg heating supply to oil burner, lights) on a plug which is either
plugged into a suitably fused utility side socket, or unplugged and
replugged into another totally isolated socket fed by the generator. Indeed
this is an approach occasionally used in the UK where someone may which to
power the gas/oil heating system and maybe a lighting circuit from a small
genny. This would be the recognised poor mans method, though it is sound and
not automatic.

Anything else is a disaster waiting to happen. It is also not just about you
- you have obligations not to back feed your generated supply into an
otherwise dead utility supply and possibly kill an innocent third party
engineer.

Sorry to be harsh, but as you seem to persist in this dangerous, unnecessary
and cheapskate approach without any regard for even the most basic levels of
good design that would be obvious to a half clued up trainee electrician,
you need telling.

Don't be a cheap sod. Either don't do it, pay someone to do it or buy the
appropriate equipment and stop trying to use the crap in your garage spares
box.

And FFS go and read your bloody regulations man:

http://www.nfpa.org/aboutthecodes/Ab...ookie_t est=1

Tim

--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.