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Parallel controlers - how to connect

I have two controllers in parallel to a bathroom fan: Honeywell HVC001 and DewStop FS-100. The DewStop functions properly but the Honeywell apparently resets its clock/timer whenever the DewStop powers the fan (otherwise the Honeywell operates as specified; the Honeywell control display will blank out while the DewStop is running the fan.) How should I connect these in parallel (or what do I add?) Honeywell's tech support says that they've no ideas or suggestions. While I could rewire these controllers so that only one controls the fan, both are required for this application (one be city code; the other by user specification.)

Re: Parallel controlers - how to connect

You could have the controllers control two separate relays which control the fan. That way they would be isolated from each other.


Re: Parallel controlers - how to connect

The problem is that the Honeywell controller doesn't have a neutral; rather, it is powered by being wired in series with the load. When the DewStop (which does have a neutral) turns on, it short-circuits the Honeywell controller, rendering it unpowered. (It would be the same as if you jumpered a wire across the leads of the Honeywell.)

You can't wire these controllers in series, either. There's just no way to make the Honeywell work with any other switch or controller.

I recommend finding a programmable timer that has a neutral; it should be compatible when wired in parallel with the DewStop. It probably won't have all the features the Honeywell has, though.

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