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Home Repair - - If it ain't broken, don't fix it. Otherwise look here.
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Posted by on May 25, 2006, 11:31 am
I would like to control a single pump from two power sources on a
mutually exclusive basis. That is, the pump is connected to either the
grid or a generator, but not both at the same time. Would a standard
"3-way" type switch do this? If I understand correctly, such a switch
is a single pole, double throw switch. If I hook a hot (black) from
the generator to one brass screw on the switch and the other hot (grid)
to the other brass screw on the switch, run a neutral (white) from the
silver screw on the switch to the hot side of the pump (recoded black
at the pump end), and connect the neutrals (white) from both the grid
and the generator to the neutral pole on the pump, will it work? Then
when I throw the switch one way, power goes from the generator to the
pump; throw the switch the other way, power goes from the grid to the
pump, but at no time can the generator or the grid back feed each other
if they are both hot at the same time, nor can the pump be fed hot from
both the generator and the grid at the same time?
grid------------hot(black)-------------------switch hot A
generator --------hot(black)--------------switch hot B
grid and generator----------neutral(white)-----------------switch
neutral
grid--------------neutral(white)---------------------pump neutral
generator------neutral(white)---------------------pump neutral
switch neutral(white)---------------------------------pump hot(recoded
black)
Then, switch thrown one way completes grid circuit to pump and
disconnects generator circuit to pump; switch thrown the other way
complete generator circuit to pump and disconnects grid circuit to
pump.
Have I got it right?
Bruce Rieck
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Posted by Ignoramus5457 on May 25, 2006, 11:52 am
If that is a 120V circuit, yes, a three way switch could switch a
power source. Note, however, that regular three way switches are not
guaranteeing that one connection would be interrupted before another
connection is made (break before make). So switching may momentarily
connect your generator to the grid, with possibly disastrous results
(that momentary connection may possibly weld instantly if both
generator and grid are connected together while the grid is live, or
electric current could be sent to the grid when relair workers are
working on lines, etc).
It is not a good idea.
You should look for something else. I would just make two outlets, one
powered by the grid and another powered by the generator, and would
plug the pump into appropriate outlet.
i
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Posted by on May 25, 2006, 12:11 pm
Thanks, I'll think about that. Do you know if I can buy a 120V break
before make 3-way switch?
Bruce
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Posted by Pop on May 25, 2006, 1:39 pm
bfrlaw@sbcglobal.net wrote:
> Thanks, I'll think about that. Do you know if I can buy a 120V
> break
> before make 3-way switch?
> Bruce
Yes, you can. Look for a rocker type that has 3 positions: ON1,
OPEN, and ON2 setup. That way you insure you get the
break-before-make action that you need.
Pump Hot should go to the COM of the switch. The two Load pins,
or whatever they might be labeled, go to the genset and house
power as appropriate.
The center, OFF or OPEN position of the switch connects to
neither, and thus forces the break before make.
A place called Emergen has such switches; they're commonly used
in transfer switches, which is what you're trying to make.
HTH,
Pop
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Posted by Joseph Meehan on May 25, 2006, 1:44 pm
bfrlaw@sbcglobal.net wrote:
You can find what you want here:
http://www.green-trust.org/generator/genny_install.htm
It's called a transfer switch. Don't try and use some do it yourself
toy. I assure you your local power company workers will not be happy. It
is really IMPORTANT to do this right.
--
Joseph Meehan
Dia duit
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