# Interference with 2 Zigbee wall-socket dimmers solved

I have 2 “Gang Zigbee Dimmer Module” QS-Zigbee-D02-TRIAC-LN dimmers in a dual 2-way setup sharing a 2-gang wall-socket in my stairwell. (“twee hotelschakelingen in het trappenhuis met een dubbele schakelaar” in Dutch). Some of the wires share some pipes in the wall, over a length of several meters. And this setup suffered from interference. Sometimes, lights switched spontaneously on and off. And when I switch the lower light (on floor 0 or 1), the upper light was toggled as well (on floor 2). Clearly, there was quite some interference. When measuring the AC signal on a wire that was disconnected on both ends, it still showed 45 V. Making it not floating helps, I could connect it to both L or N (not at the same time of course) and no protection was triggered, so it was really floating, but the parasitic voltage came from capacitive coupling between the different wires sharing the same duct. This coupling made the switching signal to the dimmers interfere with each other, presumably.
Anyway, to cut a long story short:
I solved it by putting a ‘pull down’ resistor of 1 MOhm between the S and the N input of the dimmers. Normally, when switching with a wall-switch, S is connecting to L. By tying S to N, this ensures that S is not triggered by interference that puts a tiny signal on S towards the L voltage.

What type of resistor?

They do have a peak voltage rating that should not be exceeded or they could breakdown and cause a fire. This is independent of the power rating max voltage ( V = P/I ) and depends on the physical construction of the resistor.

Typical 1/4W and 1/2W resistors are only rated at 250Vpeak.

The Dutch system uses 230Vrms according to Google. So you want a resistor with a peak voltage rating of more than 230* sqrt(2) = 325V. Preferably a lot more. Like 500V.

Check these search results

Good point. The resistors may not be rated for high voltage, I didn’t pay attention since I didn’t realize this.
What about 3 resistors of 330kOhm in series?

Yes that would be good.

Or, 1W resistors are usually rated at 500V.