Multiple Circuits in one switch

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Salvador Santos

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Good day!

Need some help on our installation for lighting circuits and exhaust fans. The Infos are:
1. Lighting circuits controlled by 3-way switch.
2. Exhaust fans to be integrated with the lighting switch so the exhaust fans will only run while the lights are on.
3. Lighting circuits and exhaust fans are being fed on different Circuit breakers.
4. The minimum number of exhaust fan circuits is two.

I'm planning of using a contactor but I have little experience with it especially if our control switch is a 3-way switch. Can this be done?:? Will there be any violation of the code?

Need your inputs and advice.:D
 
One question. Do you want the fans to turn on every time the lights do, or still be switched and available to turn on only when the lights are on, and if you need the fans switched separately, does there have to be a fan switch at each location.
It can be easily accomplished in either scenario.

I
 
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Dennis Alwon said:
Why not just make the fan the same circuit as the lights? The 3 way can control the light and fan together.
Click to expand...

I don't know the OPs situation but we often have to combine 277 volt lighting with 120 volt exhaust fans.

We also do not know if this is a simple low power ceiling exhaust fan or a larger roof mounted fan.
 
Dennis Alwon said:
Why not just make the fan the same circuit as the lights? The 3 way can control the light and fan together.
Click to expand...
Not possible if the minimum number of exhaust fan circuits is two...

Which begs us to ask why two exhaust fan circuits? Why not lights and fans on one switched circuit?


The biggest problem I see with the proposed design using a contactor, is location of fans coupled with placement of the contactor versus location of the lighting switch leg... possibly requiring extra wiring to get a switch leg "monitor" line where needed. A possible alternative to hard wiring the monitor is using a current-sensing relay. For example:

http://www.crmagnetics.com/Products/CR-4395-P7.aspx

(Note this is not a product endorsement)
 
Given that there are 3 circuits involved I would just opt for a 2-pole contactor or relay to control the two fan circuits. The coil would operate from the lighting circuit.
 
augie47 said:
One question. Do you want the fans to turn on every time the lights do, or still be switched and available to turn on only when the lights are on, and if you need the fans switched separately, does there have to be a fan switch at each location.
It can be easily accomplished in either scenario.

I
Click to expand...

Yes! The designer requires that the fans will only be on while the lights are on.

Additional info.:
1. Supply voltage is 380/220V, 50Hz
2. Both the lights and the fans are 220V.(BTW it is not just exhaust fans, there is also supply fans interlocked with it.)
3. Lighting circuits are on separate CB.
4. Supply fans and exhaust fans are on the same CB.
5. The building is a 14Mx29M Latrine. There are entrances on both ends. Both end have 3 pairs of supply fans and exhaust fans.
6. The designer did not gave any details on how to connect the switching of the fans with the lighting switch.
7. There is just a note that says that the fans will be interlocked with the lighting switch to ensure that the fans will only run while the lights are on.

So my idea is to put a contactor that is controlled by the lighting switch.
 
Dennis Alwon said:
Why not just make the fan the same circuit as the lights? The 3 way can control the light and fan together.
Click to expand...

This is what I thought of in the first place. But when I discussed the idea with my manager, I was told not to deviate from the design. The designs have already been approved and design variations will take a long time again to be reviewed.

So I have no choice but to look for ways on how to interlock the switching of the lights and the fans while being on separate circuits.
 
ActionDave said:
Sure it can be done. Common on the three way controls the coil on a two pole contactor. One pole is the switch leg for the lights the other pole for the fan.
Click to expand...

he is going to need more than 2 pole contactor, probable 3 or 4 pole contactor, based off the number of circuits he is trying to control.
 
jusme123 said:
he is going to need more than 2 pole contactor, probable 3 or 4 pole contactor, based off the number of circuits he is trying to control.
Click to expand...

There are 3 circuits involved, the 3-ways will switch the lighting circuit and the coil. The 2 pole contactor/relay will switch the two fan circuits.
 
1. Lighting circuits. . .
2. . . .the exhaust fans will only run while the lights are on.
3. Lighting circuits and exhaust fans are being fed on different Circuit breakers.
4. The minimum number of exhaust fan circuits is two.


A1. Supply voltage is 380/220V, 50Hz
A2. Both the lights and the fans are 220V.(BTW it is not just exhaust fans, there is also supply fans interlocked with it.)
A3. Lighting circuits are on separate CB.
A4. . . .fans. . .are on the same CB.
A5. Both end have 3 pairs of supply fans and exhaust fans.

Search on

"truth table" logic

So the relevant truth table is as follows?
lights and fans are controlled by the same signal that asks for fans (from 2)
lights/fans on separate CBs (from 3 & A3)
lights/fans run on same voltage (A2)
all fans are paralleled (inferred from above)
all lights are paralleled (inferred from above)

I wasn't sure how to handle #4.
 
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