On Sat, 13 Dec 2008 13:21:44 -0500, "Twayne"
wrote:

My gas furnace is hard wired to the main panel. In the event of an
extended power outage in winter, I'd like to have the option to run it
off my small Honda generator. The only real electrical draw is the
small 110V blower motor.

If we were in for an extended outage right now, I would probably just
jury-rig it with wire nuts and a sacrificed 12ga extension cord. I'd
like something a little more... sophisticated, something that is ready
on a moment's notice.

What if I:
1. Cut the existing hard line above the furnace and install a box with
an L5-20 twistlock socket.
2. Continue the hard line to the furnace from a second box adjacent to
the first.
3. Bug a short piece of 12-3 flexible cord to the hard line in the
second box.
4. Terminate the flexible cord with an L5-20 twistlock plug.

Is this kosher with NEC? Would running flex cable from the socket
clear to the furnace be a more acceptable solution?

You could probably do that, but you seem to be saying you don't have a
transfer switch, making such an arrangement against code because you
don't mention anything about preventing backfeeds.


Backfeeds?

How the heck do you get a backfeed when you unplug something from one
power supply and plug it into another one?
Absolutely IMPOSSIBLE.

What he has is a double pole, Infinite throw,break before make,
manually operated switch. Can't get better backfeed protection than
that.


What you might use
safely would be a double pole, triple throw (off in center) switch for
break-before-make connections.
I think if you check with your local code enforcement office though
you will find that only a transfer switch and probably a separate
outdoor disconnect point is acceptable.

If you already have a transfer switch and the only problem is exactly
as stated, then a switch as described would suffice nicely. They're
also fairly common switches, especially if you live around any farmland.
I picked one up from Agway in fact. Mostly you just need to be sure the
switch goes through an open ckit on the way from one connection to the
other. Most switches are of the make before break types, meaning they
temporarily connect BOTH sources for an instant as the switch is thrown.
Middle-off is an easy way to avoid that. Besides, you also need a
disconnect method, and the middle off provides that, too.

HTH

Twayne