Ceiling fan light flickers when fan is used

Question

I have a double-gang box with a Leviton dimmer switch, a Lutron fan switch, and ran 14/3 to a Hunter 53408 ceiling fan.

I wired everything up and the controls work well, independently; the Leviton dims the T12 3.5W LED bulbs and the Lutron adjusts the fan from low to medium to high.

When both are turned on and I adjust the Lutron speed, the bulbs will sporadically flicker off and on. This does not happen every single time but there's a 50% chance that a flicker occurs when adjusting the fan speed.

Do I have a hardware incompatibility?

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One guess is that the Lutron is causing some weird fluctuation on the neutral but I'm no expert.

My second guess is that the leads for the fan versus light is not adequately separated inside the fan housing.

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Per request, below is a wiring diagram. I made it from memory so if something looks off then please request clarity.

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Update 1:

Adjusting the ceiling fan speed will sometimes make the ceiling light stay on at full brightness after flickering. Turning the Lutron on or off also affects the behavior of the light.

The flicker will also affect a dimmer+light on the same circuit in an adjacent hallway. Same Leviton dimmer but this has a Great Value bulb. This light always returns to normal after a flicker.

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Update 2:

Leaving the Lutron on high and using the pull strings on the fan causes zero issues for the bulbs.

There is another light on the same circuit which is not dimmable and it experiences zero flicker.

Answer 1

Based on the diagram, I see two problems. I don't know whether or not they would cause these exact symptoms, but they are code violations and not good. Fix them and the rest of the problem may go away.

2-wire cable between 3-way and 4-way switches

With a traditional (not "smart") setup, you must have 3 wires between any set of 3-way and 4-way switches. Two of the wires are travelers, each carrying power some of the time depending on which switches are up vs. down. In this diagram, those are the black and white wires.

Ground is irrelevant and is connected here properly, but has nothing to do with this issue. Ground is not neutral. Ground is not counted as one of the wires in branch circuit "2 wire" or "3 wire" or "4 wire" cables, because you always need it and it doesn't usually carry current except under fault conditions. (Some smart switches can use it, but that is a special case.)

The third wire, which is not present here, can be:

• Neutral
• Hot
• Switched Hot

depending on the configuration.

Currents are supposed to be equal/opposite. That cancels out certain issues that can cause heating in wires, among other things. I don't quite understand the physics of it, but this is a real issue and required in code. Basically any time wires are outside a box they need to match up in this way.

Which leads to the second problem:

Unbalanced Neutrals

Neutral is always supposed to have the same current (but opposite) as the matching hot or switched hot wire. From the fan/light switch box ("problematic switches") to the fan/light, the switched hots and neutral are 100% balanced.

However, from the fan/light switch box down to where everything merges together (purple junction near "Power (one circuit)"), the neutral wire is carrying the light and fan power but the hot wire is only carrying the fan power.

There is no easy solution. The proper solution requires running /3 cable. And not just replacing the /2 that is there with /3, but also reconfiguring so that instead of:

• Panel -> left 3-way -> 4-way -> right 3-way -> light

it is:

• Panel -> right 3-way -> 4-way -> left 3-way -> light

The more practical solution is likely to be:

• Replace the dimmer with a "smart" dimmer that can use either wireless (battery powered but look like regular switches) remotes or wired remotes that only need 2 wires (including not just another 3-way but also the 4-way in the middle).

Answer 2

I know this thread is old but the Lutron dimmer switch you are using is not supposed to be used with led bulbs per manufacturer. It says compatible with incandescent and halogen bulb types.