According to Toller :

wrote in message
oups.com...
I am considering purchasing a 3000 watt emergency generator. At this
size, some generators are 110/220 and others are only 110 volt.

I can backfeed 2 receptacles on the opposite side of the box with 2
extension cords and feed any 120 loads within the breaker limits.

If you do this, and I sincerely hope you will not, make darn sure all the
240v breakers are off. In fact, make sure all the breakers are off.

There is no point in feeding the panel with a piddly little 3Kw generator.
Use extension cords to the devices. He's going to have to juggle the loads
anyway.

But what about the water heater? How would you suggest that I connect
120 across it?

If I were going to do it, and I wouldn't do it, I would cut the cable to the
water heater, put a 120v plug and outlet on it. Then it is a simple matter
to run the heater off an extension cord. Or, if you are really crazy, plug
it into a backfed 120v outlet and run it that way. Make sure you use a 30a
plug and outlet; although it won't draw that much on 120v, it will on 240v.
I suppose it would be better to use a 240v plug and outlet, and make a
converter with a 240v outlet and a 120v plug, though it is so foolish it
really doesn't matter.

I'd use a 240V plug, and a short adapter cord for use with the generator.
[120V plug to 240V socket.] The 240V plug has to be wired adequately
(probably #10) for full line current, the adapter and extension cord
need only be beefy enough for half the HWT's amp rating (14 or 12ga if
long).

This is a code violation tho without very careful attention to wire
types (even then, but never mind).

But don't do this - see below for a simpler and less expensive
alternative.

It sounds like an accident waiting to happen. Besides, I doubt the heater
will get hot enough to work. I have a 240v baseboard heater wired to 120v.
It is fine for late spring and early fall when I use it, but it barely warms
up.

120V to a 240V water heater works just fine. My inlaws had theirs wired
that way by some idiot electrician. The drawback is that recovery time is
_abysmally_ slow (4 times slower). You can imagine what a house with
this problem and four women in it is like when it comes to showers.

Fixing that water heater recovery time went a long way towards them
allowing me to marry their daughter ;-)

Don't do it, because it's tremendously wasteful, and when you're on a generator,
it's a bad time to waste power.

It's more effective/useful to buy an 120V electric kettle (it'll
cost less than the adapter cord alone and doesn't require screwing around
with the HWT circuit or the inevitable code violations). Heats a lot
faster too. Or use a propane stove.

[240V to a 120V water heater also works okay, for a couple of weeks, then
the elements eventually fry.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.