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I just installed this new fan in the bathroom: Utilitech Ventilation Fan 1.5-Sone 100-CFM White Bathroom Fan

However, if I use regular toggle switch, it works fine. But if I use countdown timer switch, Lutron Maestro Digital Countdown Lighting Timer specifically, it fluctuates in power like ON and OFF constantly.

I read the reviews of the fan product and someone mentioned the switch is not compatible since the fan is low wattage. I am not sure if I understand correctly. This exact same timer switch works with another fan model but not Utilitech.

Is there any specific configurations of the timer switch I should look for when buying one for the fan?

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  • Is there a neutral at the switch box? Can you post photos of the inside of the switch box, even? – ThreePhaseEel Dec 23 '19 at 5:03
  • Yes there is neutral BUT when I connect to the switch, I pigtail all the neutral then one black to power and one black to the fan. Is that the problem? – HP. Dec 23 '19 at 5:05
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Take it back and get a different timer

The stock Lutron MA-T51 does not need neutral; however, it accomplishes this by trickling power through the load. This is fine for large loads, but for low loads, (less than 40W or 0.3A), it causes the repeated on/off cycling behavior you are observing. (This is mentioned in the troubleshooting section of Lutron's installation guide for the MA-T51, even.)

So, you'll need to take it back and exchange it for a Lutron MA-T51MN, which does require a neutral connection, but is compatible with any load within its ratings as a result of not having to trickle its own operating current through the load.

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There are actually two problems, and they are related:

Low Power Fan

First I found a customer review on the Lowes web site that said:

I gave this only three stars as no where on packaging or instructions is there any note indicating this will not work with high efficiency bathroom fans. I spent many hours troubleshooting my Broan XB110L only to find during internet searches that this timer causes erratic fan operation. Actually in my experience this timer results in a fan that never reaches full speed and labors erratically at very low speeds.

which matches your problem pretty closely. And then I found this comment from a Home Depot customer:

Note: This timer requires a load of at least 40 watts to operate properly. and that matches your problem exactly. Your fan is rated at 30W. Not clear if that is Fan + Light or just Fan. But even if it is just the fan, the LEDs are 13W so that would be a total of 43W - and likely less because the fan motor is probably listed at the high end of its usage (e.g., startup).

which led me to the definitive answer in the installation instructions:

40 Watt Minimum

  1. Do not use where total load current is less than 0.3 A 40 W or greater than 5 A

which confirms the problem.

Not LED Compatible

I was at first a bit surprised at this, as the device seems quite up-to-date and even uses LEDs in its own design. But both Lowes and Home Depot list it as not LED compatible. Since your fan has LED lights, that's a no-go right there.

Why is there a minimum load? There are three ways to power a smart-switch/timer/motion-detector/etc.:

  • Neutral

Neutral requires a neutral wire. Many older homes don't have neutrals in the switch box, so it is a marketing advantage to have a product that doesn't require neutral - fewer returns due to "can't install it here". This timer does not use neutral.

  • Ground

Ground is a general "no, you can't do that" but it is allowed when properly designed but has a limited amount of current allowed for the "smarts" of the device. This timer does not use ground.

  • Leak through switched hot

This is the only option left! Works great with incandescent & halogen but does not work well with LEDs. And I suspect they have some tricks that just don't work well unless there is a large load so that the timer's own usage is "small" relative to the fan/light load.

Bottom line: SEND IT BACK

Recommendations

Look for a timer that says:

  • LED Compatible - That indicates it doesn't "leak current"
  • Requires Neutral - That tells you how it gets the necessary current
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  • my whole house is power by timers and motion switch and uses LED and I have no neutral setup so not sure about ur statement about LEDs – FreeSoftwareServers Dec 24 '19 at 4:11
  • @FreeSoftwareServers As I noted in my answer, timers & motion sensors have to get power from somewhere. That means neutral (which you say you're not using), ground (relatively unusual but definitely possible with some setups), leak through switched hot (doesn't play well with LEDs) or (rarely with timers, almost never with motion sensors) batteries. You have to have one of those possibilities. – manassehkatz-Moving 2 Codidact Dec 24 '19 at 4:36
  • Here is an example that says it works with LED and doesn't require Neutral. Leviton IPS06-1LW 600-Watt Incandescent, 150-Watt Led/CFL Occupancy Sensor (Auto on/Auto Off), Single Pole or 3-Way, amazon.ca/dp/B00BUZQVMU – FreeSoftwareServers Dec 24 '19 at 5:09
  • @FreeSoftwareServers That's very interesting. According to the specs, IPS02/IPV02/IPS05/IPV05 all require ground. IPS15/IPV15 require neutral. IPS06 (which you linked)/IPSD6/IPVD6 don't require ground or neutral. They are more limited (no motor, fluorescent ballast or resistive loads) but all work with LED & CFL. Not sure how they do it! – manassehkatz-Moving 2 Codidact Dec 24 '19 at 5:27

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