I need (in emergency only) to run my deep well pump off a generator,
its 220V. I want to cut into tha wire that's in the basement going down
the wall. There's a switch there to turn if off in emergency. I want to
put a recessed male plug outlet next to that, which my generator will
The question is, what's the switch I should use? Don't really want to
buy a $200 transfer switch. Just a LINE-OFF-GENERATOR 3-position
switch, so that I can't feed back into the mains supply system.
Thanks in advance,
: >I need (in emergency only) to run my deep well pump off a
: > its 220V. I want to cut into tha wire that's in the basement
: > the wall. There's a switch there to turn if off in emergency.
I want to
: > put a recessed male plug outlet next to that, which my
: > plug into.
: > The question is, what's the switch I should use? Don't really
: > buy a $200 transfer switch. Just a LINE-OFF-GENERATOR
: > switch, so that I can't feed back into the mains supply
: > Thanks in advance,
: > Dean
Pop ( email@example.com) said...
DOUBLE pole, DOUBLE throw, Center off.
In switch language, the number of "throws" indicates the number of
"destinations" for the power to go. A "center off" position for the
switch does not send the power anywhere (or from the point of view of
the person installing it, there are no terminals associated with the
center off position). There are only two throws.
This is the key to what is needed. We have a Square D transfer panel
that feeds certain branch circuits from either the utility power or
a generator. It uses common power busses with eight breaker positions.
The two sources are connected through back fed breakers that have a
mechanical interlock that not only allows only one to be on at a time,
but forces the one that is on to be shut off before the other can be
turned on. The inspector took the time to ensure that a make-before-break
operation existed, for both going from utility to generator, and the
other way around.
"Never ascribe to malice what can equally be explained by incompetence."
Throw indicates whether the switch makes contact in the direction it is
thrown. Single throw indicates that the switch has two contacts that
make in one position. Double throw indicates that the switch closes
different contacts in each position.
Poles represent the number of contacts that operate simultaneously. In
the US, 120 volt switches are typically single pole with the neutral
side connected unswitched to the load. 240 volt circuits use double
pole switches to open or close both sides simultaneously.
120 volt on-off switches are typically SPST (single pole single throw),
and 240 volt switches ate DPST (double pole single throw). A 120 volt
3-way switch is SPDT (single pole double throw).
So its double throw, double pole, 3-position switch, center off.
If I add to that a 240V recessed male plug, I might as well get a
single terminal generator transfer switch, that's the same thing I
If I were doing that I'd just install a female socket wired to the 220V
feed from the existing switch and put a flexible cord with a matching
male plug on the line going down to the pump. With the two plugged
together you'll be back where you were, and if the power goes out you
just yank the plug out of the socket and plug it into the genny, using a
suitable extension cord if needed.
I wcan't comment on the codeworthyness of that kind of setup, but it
will acomplish the job electrically without your needing to buy a new
Considering that the local inspectors passed the central vac
installation in our home when it was built, and the vac unit is
permenantly mounted to a wall but is powered by a flexible cord plugged
into an adjacent wall receptical, I'd guess it's not toooo bad a way to
do it, huh?
Jeff I never thought of that. Are 220V plugs and sockets the same as
the 110V ones?
Thanks all. I'm not sure what the number of throws or poles is, but I
assume they say this on the switch? Could I also ask - do these look
like regular wall switches?
Great. Thanks for the help.
What kind of connector do you recommend? The generator will have a
typical 220V cable, I assume it should me just the same as that (male
version) and that this should be close to the existing emergency switch
(not sure which side though)
IMO Dean is asking questions which indicate considerable lack of electrical
Recommend get someone knowledgeable to help; otherwise something dangerous
could occur? Such as feeding generator AC back into the hydro lines; with
him being responsible for an electrocution?
There are many configurations of NEMA plugs.
FWIW we use three pin plugs which have a 'conventional' looking ground pin
but with horizontally polarized pins, for 230 volt. Can't recall if they
are 15 or 20 amp capacity.
Normal 115 volt plugs have vertically polarized pins.
But we also have some older three pin plugs for a couple of 230 volt
applications which have a 'flat' third or ground pin and 'slanted' live
pins. Perhaps somewhat similar IIRC to Australian 230 plugs?
Poster needs to know how to wire these correctly and safely! It's worrying!
PS. I finally came across a double pole switch to install on our 230 volt
bench saw. Until I get round to doing that will continue to unplug
completely between cuts, for safety. While blade is lowered below the table
when saw not in use, also thinking about adding an extra 'safety' interlock
device to prevent an occasional user or child from switching on the saw in
my absence. Possibly something that goes on my keychain?
Any ideas? Maybe a small permanently short-circuited two pin plug to push
into a socket wired in series with one leg of the 230?
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.