Two electrical devices, one switch

[bfrlaw]

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

[Ignoramus5457]

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

[bfrlaw]

Thanks, I'll think about that. Do you know if I can buy a 120V break before make 3-way switch? Bruce

[Pop]

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

[Joseph Meehan]

You can find what you want here:

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.

[Ignoramus5457]

Or, if he wants a cheap, safe $5-10 solution, done tomorrow, he can have two outlets: one powered by the grid and one powered by generator. He could manually plug the pump to the appropriate outlet when needed.

I think that going this route is a no brainer in case of a pump.

i