Weird Panasonic bath fan problem

Status
Not open for further replies.
E

edlee

Senior Member
Location
Western Massachusetts
I roughed in a Panasonic bath fan and now am trimming it out. It is designed to run continually at a low speed and when someone wants to use it as a bath vent then they hit a switch and it boosts it to high speed. So the wiring consists of bringing a constant hot and neutral to the fan and from the control box on the fan dropping a switch loop down to the wall booster switch.

Problem is the switch loop, which is integral to the control board, switches the neutral. Not the hot. When I roughed it in I called Panasonic and asked them about this and they told me the wiring diagram was correct.

Fine. Since the homeowner wants a timer on the wall I had figured I would just put in a 2-wire spring-wound timer. But the builder wants an electronic push-button timer. I told him I didn't know if I could make it work.

I tried a 2-wire PB timer and while it started the fan, it wouldn't time out and shut off. I tried a 3-wire PB timer, reversing the polarity (brought hot to white wire and neutral to black wire) and, guess what, it works.

Question is, would wiring in a timer reversed polarity be a reasonable and safe solution? Or simply reversing the polarity of the fan wiring itself? I don't really like it!

The circuit BTW is AF/GFI protected.
 
I think that a lot would depend on whether the switch loop is carrying actual fan load current when closed or is simply a logic input to the fan electronics module that happens to have 120V on the control lead when the switch is open. And is the 120V on that lead power limited? I would hope that it would be since you are "shorting" it to ground.
Switching the neutral is common in control circuits, although many try to avoid it when using relays.
 
GoldDigger said:
I think that a lot would depend on whether the switch loop is carrying actual fan load current when closed or is simply a logic input to the fan electronics module that happens to have 120V on the control lead when the switch is open. And is the 120V on that lead power limited? I would hope that it would be since you are "shorting" it to ground.
Switching the neutral is common in control circuits, although many try to avoid it when using relays.
Click to expand...

There is an internal in-line fuse in the fan so would that in effect be power-limited? The voltage on the loop is 120 but likely it is part of the control circuit.

What do you think about reversing the polarity of the timer?
 
edlee said:
FV-05-11VKSL1 with plug-in speed module
Click to expand...
Unit is UL lsted with conditions (GFCI, insulation), and wiring diagram show switch connection to two red leads (and says non-powered). Doesn't matter if one side connects to source neutral.
 
Smart $ said:
Unit is UL lsted with conditions (GFCI, insulation), and wiring diagram show switch connection to two red leads (and says non-powered). Doesn't matter if one side connects to source neutral.
Click to expand...

My question is about the timer. If one side is connected to the source neutral and my timer sends line voltage to it, are you saying it doesn't matter, it will work anyway?
 
edlee said:
My question is about the timer. If one side is connected to the source neutral and my timer sends line voltage to it, are you saying it doesn't matter, it will work anyway?
Click to expand...
It's a control loop. You have to connect it as such, including the loop switch. Now what controls the in-loop switch is totally up to you.
 
Smart $ said:
Now what controls the in-loop switch is totally up to you.
Click to expand...

I want a residential grade push-button timer with an end switch. As far as I know, such a thing doesn't exist. So I'm considering reversing the polarity of a residential grade electronic timer, which offhand does not seem like a great idea even though it apparently works, and I'm asking for opinions or other suggestions.
 
Last edited:
edlee said:
I want a residential grade push-button timer with an end switch. As far as I know, such a thing doesn't exist. So I'm considering reversing the polarity of a residential grade electronic timer, which offhand does not seem like a great idea even though it apparently works, and I'm asking for opinions or other suggestions.
Click to expand...
Would work, yes, but technically a Code violation.

Consider using an interposing relay... perhaps a "relay in a box".
 
Smart $ said:
Would work, yes, but technically a Code violation.

Consider using an interposing relay... perhaps a "relay in a box".
Click to expand...
Without the relay, the timer would have to be one which had both hot and neutral connections, rather than being dependent on current through the load. But if the relay coil was a large enough load to keep a two terminal timer happy, then that would seem to be ideal. You would have to feed the relay from a constant hot wire rather than the control lead.
 
I would not want to install anything not per code or not as per manufacture. You become liable if something goes wrong.
 
150325-2351 EDT

edlee:

You have not adequately defined the devices you are working with and how they operate. Nor have you run appropriate experiments to learn more about the characteristics of of the devices.

How many wires does your timer have? Is there a neutral wire? My assumption is 3 wires and a required neutral. If this is the case, then power needs to be applied between hot and neutral, probably hot is black and neutral white. Next with high probability we can assume that the output switch is between hot and an output wire. Output is probably red.

Next we assume the fan has at least a control wire, but possibly it is a direct wire to coils on the motor. You stated this wire gets connected to neutral to make the fan run fast. If you measure the current in this wire when connected to neutral, then you can determine if it is simply a control wire or a power wire.

You have said that if you connect the timer backwards then it works. If you mean connect the timer black to neutral, white to power hot, and red to the fan control line, based on my above assumption of timer wire colors, then I would expect the system to work just fine.

Should you do this? No because of possible listing problems, and total confusion for some other person doing service work in the future. Could even be you. Obvious solution is a relay, but that presents problems of where to put the relay and what relay to use.

The best solution is a mechanical timer. If you can find an electronic timer with an isolated output switch, a 4 wire timer, then that would be a good solution.

.
 
Thank you gentlemen for the replies. They pretty much reflect what I was thinking, and I learned a few things too.

RIBs are cool but in this situation I don't have a place to put one, so mechanical timer seems to be my only option.
 
Haven't gone to the Panasonic specs and haven't installed this particular config, but from previously looking up options I'm surprised that Panasonic's configuration is so limiting in options. I thought this option (constant on low speed with overide) was a big selling point in newer "tight" construction and that options like occ sensors were also usable to control......it seems like this system is not very well thought out.....does Panasonic have anything to say about it?
 
edlee said:
Thank you gentlemen for the replies. They pretty much reflect what I was thinking, and I learned a few things too.

RIBs are cool but in this situation I don't have a place to put one, so mechanical timer seems to be my only option.
Click to expand...
Are you at trim out stage?

Can you run any more wires to timer location?
 
Digital timers usually require a neutral. In the past the equipment grounding conductor was used but that is no longer compliant.
 
Dennis Alwon said:
Digital timers usually require a neutral. In the past the equipment grounding conductor was used but that is no longer compliant.
Click to expand...
Having a neutral, so-to-speak, isn't really the problem. The fan unit has a switched control loop, which one side is directly connected to supply neutral through the control "board". The timer would have to switch the neutral, and practically all electronic in-wall timers only have three leads--hot, neutral, and switched--and the switched lead is a switched hot.
 
Status
Not open for further replies.
Top