I sometimes see three terminal rocker/toggle switches, and one terminal is a different color than the other two.

Here is an example:
switch
(Image from ebay.com)

What does the colored terminal indicate?

up vote 12 down vote accepted

I have found a common convention with the off-color terminal being "ground", meaning it is connected to the internal light and is non-common (doesn't connect to both sides).

My interpretation is that the different colored terminal is used to identify between load and power to the internal light. The "Ground" terminal is indicated because the other two terminals operate as a normal two terminal switch, while Ground is not supposed to carry load current.

Note that conventions are just that, and the datasheet should always be referenced.


It's hard to see in the photo, but this switch has the pins numbered on the black plastic.
Datasheet

iluminated E-switch datasheet diagram

E-switch datasheet diagram

(Images from ckswitches.com)

The circle with an "X" in it is generic symbol for a "lamp". So there is a lamp and a resistor in the switch. Typically, neon lamps will be used for mains AC, and nowadays LEDs will be used for lower, DC voltage (as seen further below).


Some switches will are labeled outright like so:

illuminated toggle switch
(Image from ebay.com)


I found this one interesting because the colored pin also has two holes instead of just one.

Illuminated toggle switch by Lumex lumex illuminated toggle switch diagram
(Images from Digikey.com)

  • is it color, or is it cheaper alloy because the lamp does not draw significant current? but then, wouldn't a simplified manufacturing process outweigh that? – dlatikay Sep 25 at 20:20
  • @dlatikay - I pondered that myself, though I don't have any data to work with in that regard. Anyone with more insight, please chime in. – Bort Sep 25 at 20:35
  • Most pins are copper-clad steel, be it a switch or a resistor lead. This give it much more strength than pure copper. Wires can be tin or nickle or brass plated over the copper. – Sparky256 Sep 25 at 20:37
  • Nickle plated wires are for crimping only. You cannot solder to nickle. Part of RoHS requirements for lead-free products. – Sparky256 Sep 25 at 20:39

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