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.

Impossible isn't what it's about. POSSIBLE is what it's about, and to
use a generator, you need a transfer switch. What I think I left out is
that his local code enforcement office is going to have the final word
on the subject; that is where he has to check. If they allow it, it's
legal. If not, it's not. It's easy to call & ask rather than put up
with rhetoric in places like this. He's going to need a transfer switch
that guarantees never backfeeding; nothing guarantess he won't hook it
up in a manner that could backfeed, whether he intended to or not.
Plus, he's not the only soul on earth that might use the generator -
they don't accept taht as an arguement. Only positive situations are
allowed, not promises.


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