count down timers for bathroom fans

[green2012]

I am curious to know if you can have 2 single pole countdown timers operating the same bath fan. I know that having 2 dimmers operating the same load is bad but a countdown timer isnt adjusting or limiting power. They are basically counting themselves down to turn off. I asked Lutron but I dont trust the answer because they want me to buy their multilocation product lol. I know the operation would be different then a 3 way way set up. If I turned one sitch on and set it to 10 min and the other fan was turned on and set to 20, then the fan would stay on for the 20 min and the other switch wouldnt be able to turn it off. In theory this sounds fine but....

 

[infinity]

Just curious, what purpose would a timer set for 10 minutes serve when you also have a timer set for 20 minutes?

 

[green2012]

I have a in ceiling bathroom fan that vents 2 different bathrooms. My example was to say I understood that the switch with the longer time setting would override the other switch and it wouldnt function as a true 3 way. That being said, would one timer hurt the other with this set up? Similarly, 2 dimmers on the same load would burn out the dimmers. Would 2 timers on the same load have the same effect even though they are glorified on/off switches and not varying the voltage.

 

[petersonra]

I have a in ceiling bathroom fan that vents 2 different bathrooms. My example was to say I understood that the switch with the longer time setting would override the other switch and it wouldnt function as a true 3 way. That being said, would one timer hurt the other with this set up? Similarly, 2 dimmers on the same load would burn out the dimmers. Would 2 timers on the same load have the same effect even though they are glorified on/off switches and not varying the voltage.

If they are dry contacts it will work fine.

 

[gar]

131005-1227 EDT

green2012:

If your countdown timer switches require a neutral connection, meaning power to operate the timer and drive the Triac switch are provided from hot and neutral, then the multiple timer switches will probably work if supplied from the same branch circuit. As said above the timer set to turn off last will be the controlling unit for the off time.

I have no problem with solid-state switches being in parallel if there is some way to provide on off control of the switch. In the case of a Triac or SCR this means drive to the gate to turn it on, and of course turn off is at the next current zero crossing.

If dimmers are of the type that requires a neutral, then my guess is that they could be in parallel. The highest set dimmer would control light level, but the lowest dimmer would set the minimum dimming level.

.

 

[jaylectricity]

If dimmers are of the type that requires a neutral, then my guess is that they could be in parallel. The highest set dimmer would control light level, but the lowest dimmer would set the minimum dimming level.

Seems like it would be the opposite. The highest set dimmer would set the maximum while the lowest would control the light level.

 

[gar]

131006-1440 EDT

jaylectric:

For explanation simplicity consider two SCRs in parallel. Anodes connected together, and separately cathodes connected together. When triggered this becomes a phase controlled half wave rectifier.

Provide separate gate trigger circuits. Make the trigger for SCR 2 turn it on at 120 degrees from the anode applied voltage positive zero crossing. If SCR 1 is not turned on at all, or somewhere between 120 and 180 degrees, then the on time of the output voltage is from 120 degrees to the next current zero crossing. And is not affected by SCR 1. So average load current is less than if SCR 2 had been turned on earlier. Thus, dim. If SCR 1 is not turned on, then SCR 2 solely determines the amount of dimming.

Keep the trigger point on SCR 2 at 120 degrees.

Adjust the trigger of SCR 1 to occur before 120 degrees. Now the output average load current and voltage is greater than what triggering of SCR 2 at 120 degrees produces. Thus, until the trigger point of SCR1 becomes greater than 120 degrees it is SCR 1 that controls dimming. Once SCR 1 trigger is greater than 120 degrees (the set-point of SCR 2), then no further dimming occurs.

The dimmer with the lowest brightness setting determines the minimum brightness level.

.

 

[jaylectricity]

You're talking way over my head. I always thought a dimmer just limited the current to whichever degree you set it.

 

[darekelec]

Does the OP have to install disconnects for timers? if yes; would it be a toggle switch installed adjecent to timer to confuse people?
430.102 Location.
(A) Controller. An individual disconnecting means shall be provided for each controller and shall disconnect the controller. The disconnecting means shall be located insight from the controller location.

 

[jaylectricity]

Does the OP have to install disconnects for timers? if yes; would it be a toggle switch installed adjecent to timer to confuse people?
430.102 Location.
(A) Controller. An individual disconnecting means shall be provided for each controller and shall disconnect the controller. The disconnecting means shall be located insight from the controller location.

The timer isn't a controller. It's a switch.

 

[gar]

131007-0928 EDT

jaylectricity:

See http://en.wikipedia.org/wiki/Dimmer for a discussion of dimmers. This will provide some basics.

.

 

[kwired]

The timer isn't a controller. It's a switch.

It is also the "controller" for the fan as would be a simple wall switch.

I would also say this fan is an appliance and art 422 would apply to it. 422.31(A) would allow the branch circuit overcurrent device to be the disconnecting means - unless the motor is over 1/8 hp.

 

[ggunn]

I am curious to know if you can have 2 single pole countdown timers operating the same bath fan. I know that having 2 dimmers operating the same load is bad but a countdown timer isnt adjusting or limiting power. They are basically counting themselves down to turn off. I asked Lutron but I dont trust the answer because they want me to buy their multilocation product lol. I know the operation would be different then a 3 way way set up. If I turned one sitch on and set it to 10 min and the other fan was turned on and set to 20, then the fan would stay on for the 20 min and the other switch wouldnt be able to turn it off. In theory this sounds fine but....

If it works otherwise you will of course have to be absolutely sure that both timers are supplied from the same leg of the 240V service.

 

[jaylectricity]

Thanks for the info, guys.

 

[kwired]

If it works otherwise you will of course have to be absolutely sure that both timers are supplied from the same leg of the 240V service.

I would hope he is supplying them both from the same leg from the same branch circuit.

It will work if the timers are a "dry contact" type of switching device as mentioned early in the thread. Basic spring wound timers would have no trouble at all, either one of them still in on position and the fan runs, both of them reach off position the fan shuts off.

It may not work if they are solid state switching devices and would depend on just exactly how they are designed to operate.

 

[GoldDigger]

I would hope he is supplying them both from the same leg from the same branch circuit.

It will work if the timers are a "dry contact" type of switching device as mentioned early in the thread. Basic spring wound timers would have no trouble at all, either one of them still in on position and the fan runs, both of them reach off position the fan shuts off.

It may not work if they are solid state switching devices and would depend on just exactly how they are designed to operate.

The least likely to work properly would be two terminal units designed to run parasitically off the current through the load.

 

[ActionDave]

The least likely to work properly would be two terminal units designed to run parasitically off the current through the load.

There you go looking for mythical creatures again.

 

[kwired]

The least likely to work properly would be two terminal units designed to run parasitically off the current through the load.

I don't know much about how these electronic timers are constructed, but would guess if only a two terminal unit, the control features of the device would be disrupted by alternate current paths. If the timer had a neutral terminal that was necessary to use for operation then this probably is not a problem.