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On Hooking
Up A Generator:
Shayde writes:
Going through the recent Want-Ad Press, I'm seeing generators ranging
from 1000watts up through 600kw (i kid you not), and engines from 3 1/2
horsepower briggs n strattons through 6 cylinder military diesels.
I'd like to explore having a backup power system for Homeport. We're WTF
up in the hills, and have an electric well pump. If we lose power, we're
out of commission.
I figure I can get by with something that'll do 100amps - which I'm seeing
for reasonable prices (anyhwhere from $300 w/out any engine up through
$1500 with a 2 cylinder engine attached to it). The question is, I have
-no- idea how to rig the power systems in the house to allow an alternative
'input'. I'm assumign calling my happy electrician would be the best way,
but I'm also thinking of the old "this outlet has a 20 amp breaker
on it, ergo is rated for 20 amps. If I have no other power, can i 'back
feed' power into the house?"
Second question to that is... what happens when the local grid comes up
again? Am I going to have little bits of generator blown all over the
place?
Curious curious...
Jim sez:
First off: are you *sure* you need 100amps continuous, especially if this
is just an emergency generator to tide you over power outages? Depending
on whether you're counting your amperage on one or both legs, 100 amps
is either 10 or 20 kilowatts... which is one big whonking generator. I
think you could get by very nicely with less. The generator I use out
in Phillipston is rated for 4KW continuous, 5KW surge, and cost less than
$400 at BJs -- new, with warranty.
That should take care of an average household's electrical needs just
fine, unless you really *HAVE* to have your Bridgeport machine running
at all times 8-)
As for hooking this up to your electrical system, there are two possibilities.
As you suggest, you can indeed "back-feed" power into your electrical
system via an outlet.
(Russ writes: And if the power company finds out, they'll have a cow.
No bull! Sparky the lineman *really* doesn't like this system.)
A buddy of mine uses such a setup as follows: He rigged a special cable
to go from the 220V output of his generator to a male 220V/30A plug. The
cable is
10-guage wire, and the plug goes into the electric dryer outlet. (If you're
going to do this, you have to back-feed into a 220V outlet in order to
make sure you power *both* legs of your service).
As for not causing sparks when the power comes back up, the easy way to
deal is to pull the main breaker for the house before you hook up the
generator, and shut down the generator before switching the main breaker
back on. This does two things; it avoids frying Sparky the Lineman as
he tries to service what he *thought* was a dead line, and it avoids your
back-feeding your precious power to your neighbors 8-)
The other possibility for hooking up is to use a manual or automatic cutover
switch made specially for the task. Commercial buildings with standby
generators do just this, and it's required by code if the generator is
to be permanently wired in. Needless to say, it's more expensive. The
cheapest manual cutover switch I've seen is about $300 at Home Depot...
Russ replies:
I've got part of my house wired for generator service, and I have such
a cutover switch. Much better for one's peace of mind.
Yep, 4KW is enough for most purposes. That's what I have, and that's what
most people used during the ice storm last January. I paid $1000 for a
John Deere 17 hours before the power went out for a week. Not a time to
shop around.
More:
What I notice is that the cutover switches I've seen are for individual
circuits... do they make just a simple, whonking DPDT switch that you
can install at the mains and be done with it? 8-)
The Rejoinder:
I'm assuming you mean an automatic DPDT switch, yes?
Any pointers on pricing for one of these bad boys? That'd be fine, then
I could just run the generator circuit to that switchover, and when there's
an outage, go out, fire up the generator, and continue playing Quake,
and when the main power came on, it'd kick back.
Crash sez:
Never, EVER backfeed a power panel with a generator or suicide cord. First
off, it's very against code. Second off, you may very likely kill someone.
Hopefully just yourself, but maybe not... more the tragedy.
Third off, you _will_ explode your generator into tiny little pieces when
power comes back online.
Install the transfer switch.
Shayde replies:
I'm a little uncomfy with this approach anyway. The last thing I want
to do is a) fry some lineman, b) fry my house, c) deal with the insurance
company when they find out my house burned down because I did something
seriously out of code. :-/
Which brings me back to... where can i get one, how much is it, and what
electrician do i have to go to bed with to get one installed?
Ted:
(A note though - what about brownouts? There are occasions when the re-powering
of the house may only temporary. Is the switch dual action? (on power
out, it cuts out, on re-powering, it cuts back to the grid?))
The automatic transfer switches are required by code to have timeouts,
which are user adjustable within certain limits. Typically the switch
will wait 5-10 seconds after a power outage before sending the "generator
start" signal and cutting over the power so that your house is fed
by the generator instead of the mains. Also, when the power comes back
on, the generator will usually waits 30-60 seconds before switching the
system back to the mains and turning off the generator.
Automatic transfer switches are *expensive*, though. With manual switches,
when the power goes out, you have to get a flashlight, stumble downstairs,
throw the switch, and start the generator yourself.
Alternatively, you might want to consider exactly how many circuits you
really want to protect. Getting a generator which can power all of the
circuits in your house is going to be way expensive anyway; 100 amps will
require a 12,000 watt continuous generator, which will run you a good
chunk of change. If on the other hand you only want to keep certain absolutely
essential services running --- a water pump, the heating system, etc.,
then you can use a much smaller generator.
In that case, you can simply insert a 15A or 20A receptacle and plug into
the cables which supply your furnance and your water pump. In case of
a power outage, you can then unplug your furnance from the circuit breaker
panel, and run an extension cord between the generator and the plug which
powers your furnance. (Most generators have one or more circuit breakers
built into their output(s).)
This is a little kludgy, and it's certainly not as pretty as a transfer
switch, but it's a heck of a lot cheaper. A lot really depends on how
often you expect to need to use the backup generator. If you consider
it to be a once-in-a-lifetime event, then you won't need anything too
fancy. If the power is unstable enough that it's going out every month
or so, then the automatic transfer switch might make more sense.
Crash:
I tried to get my electrician to install this when he put in the 40 KW
main panel, but apparently there's a quirk in the NEC that says that you
can't use flexible cabling unless one of the two following conditions
holds:
1) the equiment being cabled moves (e.g. lighting bars in a theatre) or
2) you need to decable and roll up the cabling as an aid to sanitation
(e.g. pump wiring in a a brewery or abbatior )
So, not to say I don't uncable (and _remove from the box_) the wiring
to my furnace when I need to run it off the generator, but yeah... it's
one way to do that with reasonable safety.
Of course, under those rules a garage-door opener should be hard-wired
as well, but in reality most places just allow you to plug the opener
into a convenient wall socket.
Another county heard from:
The discussion of generators, and the fact that my parents were just without
power for four days due to a freak windstorm, have made me curious: what
sort of generator set-up would you recommend for a three-family house?
(Still waiting for a verdict...)
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