i am working on a project that uses 3 double pole switches. Each switch is connected or fed from the same 220 volt breaker. Each switch when turned on powers up a separate SCR controller that varies power to one of 3 resistance heaters, the same as used in most residential electric water heaters. All SCR electronics are housed in a single non metallic box and cooled by one large 220 volt muffin fan. Is there a way to power the fan regardless of which 3 heaters are working at any given time? I hope that I have worded this clearly so that I might get some assistance from you knowledgeable members. Thanks!

 

Welcome to AAC!
What are the two poles of a switch switching? If you used one pole to switch just the 'hot' line of a controller you could use the other pole to switch the fan.

 

Hello Inheat.

Each of the 3 double pole switches can also turn on a small relay to power the small fan. Wire the contacts in parallel so any load on also turns on the fan.

 

I am switching both hot legs of the 220 volt circuit. Since this project will be used for brewing I want to kill all power to the 3 elements when all switches are off while still maintaing grounds to all 3 elements. Ernie is that relay idea good for my application, I just can't figure out how to wire them. I do however have all kinds of HVAC relays available to me.

 

BTW Thanks for the welcome

 

I am switching both hot legs of the 220 volt circuit. Since this project will be used for brewing I want to kill all power to the 3 elements when all switches are off while still maintaining grounds to all 3 elements.

This sounds like you are in USA. There is no ground connection to a heater that uses 240 volts on a dual breaker in that configuration, except the safety ground on the metal jacket. The ground is never switched. Your description does not make sense yet. Please, more information.

 

#12 you are correct I am talking about the safety ground to the metal jacket on the kettle. And yes I am in the USA. I was thinking there should be a way to use a diode as a gate so I could bring power to the fan from each switch without it feeding back to a heater that is still turned off or am I trying to over-engineer this project? A relay still sounds interesting though.

 

You can't use a diode to, "or" AC.
However, you can, "ground" a triac to one leg of 240 volts. You just have to think differently. You, "declare" one leg of the 240 to be, "common".
This, "if any, then fan"...
Make sense?

 

As a safety issue I would continue to use the double pole switches to switch both legs of the 220 volts so off is dead dead (no voltage at heater)(assuming this is how it is currently wired).

Sorry I can't post a picture of the relays but each coil goes parallel to a heater so each turns on with one heater. Then think of one: arrange the contacts so it turns the fan on. Then the next two relay contacts just go in parallel with the first set of contacts, coils for 2 & 3 go across heaters.

If I have time tonight maybe I can sketch this out.

 

Ernie the light bulb in my head just lit up. That makes perfect sense and I now have a game plan thanks to you. Guys thanks for the input here I'll put this to good use