Wiring up 24vac relay "and"/ "or" circuit

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Old 12-14-16, 03:48 PM
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Wiring up 24vac relay "and"/ "or" circuit

I am trying to energize one "fan in a can" circuit to 2 dryers. It's easy enough to connect a 24vac relay to either of the dryer's blower contactor in order to energize the fan, so that if either dryer is running it will fire it's relay. How can I wire this so that if both dryer's are running at the same time they are not both trying to energize the fan at the same time?
 
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Old 12-14-16, 04:41 PM
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Just take the hot line for the fan, run it to the common contact on both relays, and run the normally open contact on both relays to the fan. It won't hurt anything if both relays are on at the same time as long as both are controlling the same load.
 
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Old 12-15-16, 01:44 PM
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the schematic of what carbide said.
 
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Old 12-15-16, 04:31 PM
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Thanks,
Yes, that would work fine and I may just have to do something like this, but I'm trying to find a way to use the existing relay within the fan in a can instead. As you can see by the attached image of the can's wiring schematic, I'd like to be able to fire it's relay with either dryer's blower motor contactor's 24vac coil signal. I was going to wire them both in parallel to the fan's relay and that would work fine wither one was running indepently or both of the dryers were running at the same time. But then I realized by doing that if only one dryer was running I would be back feeding that 24v to the other dryers contactor coil, energizing it even if it was not called to run. I'm only concerned with the relay in the can, not the air pressure switch since I don't need to send a signal back to the dryer to start. Thanks again.
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Old 12-15-16, 06:05 PM
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You need two relays to keep the dryers isolated from one another for the reason you state.
 
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