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Old 07-22-2012, 09:47 PM   #1
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Relay Wiring - Do I have this Right?

So... I've read through the other postings and I think I've got my solution worked out but, as a simple DIY'er, I'd appreciate a double check of my plan from someone who knows more than I do.

What I'm trying to do:
I've got a standard 110V gable fan in my attic which runs off of a thermostat. I've just installed a whole house fan which runs on a separate 110VAC circuit. I'd like the gable fan to turn on when either the thermostat kicks on OR when the whole house fan is switched on via a manually operated timer switch.
Just to anticipate the question, I'm certain I need this gable fan to ventilate my attic when the WHF is on since the attic was carefully closed off after the previous owner struggled with a squirrel infestation (wretched varmints!).

What I think I need to do:
I think I need a 120VAC relay switch that takes the 120VAC switch line and the 120VAC thermostat line to NO contacts to drive the gable fan. Here's a relay I found that I think will do the job.

Things I'm not sure of:
1. I'm not quite sure how to wire the relay contacts into the existing circuits. My best guess would be to go from the switches load wire to one of the relays NO contacts, to that contact's neutral to the WHF load to the switch neutral. Is that right?
2. Can I mount this relay directly to my framing, adjacent to a box to hold the wiring connections?

Thanks in advance for your review and comments


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Old 07-23-2012, 02:17 AM   #2
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Wire the coil of the relay in parallel with the whole house fan's motor, so the relay is activated whenever the fan is on. Wire the NO contacts of the relay in parallel with the thermostat for the gable fan, so that closing the thermostat OR closing the relay turns the gable fan on. You can mount it as you suggest, but the threaded nipple on the relay module needs to be threaded into a hole in a box. I'd use a 2-gang cast metal box with a blank cover.


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Old 07-23-2012, 05:22 AM   #3
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Where is your attic getting input air when the gable fan is running? There has to be in input source or the fan will do very little good. Even with the gable fan running the WHF pushes much much more air then one gable opening can handle. Ventilated soffits, a ridge vent, another gable, it sounds like you may need more openings.
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Old 07-25-2012, 03:23 PM   #4
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I would like to do the same as you have mentioned, similiar setup. I would very much appreciate if you or anyone could post a simple wiring diagram or a link to one to accomplish this.

Here is what I have so far. I know this is not professional and I am leaving out the common and ground wires which I have all properly wired.

Basically, how would you wire a relay?

-Thanks in advance to anyone that can help.

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Old 07-25-2012, 04:08 PM   #5
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Without proper ventilation in the attic you will have condensation buildup that will eventually cause other problems much bigger. And, as zappa pointed out, that airflow will be choked if there is no eave vents, ridge vents or roof vents. What will happen is when the gable fan kicks on due to high heat, it will draw air out from the house through the WHF. If you have your AC on, the cool air from the house will get sucked into the attic. You need to undo the ventilation blockages.

As far as wiring, why not just run both fans on the same circuit? Wire the WHF switch so it turns on the gable fan by connecting it on the load side of the T-stat switch. That would solve your problem and not require relays and additional wiring.
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Old 07-25-2012, 04:12 PM   #6
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Use one of these. It will conveniently mount in a knockout at the thermostat or fan. Run a cable from contacts to the other fan to be controlled.


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