A typical toggle switch like the one pictured below. When switching a 120vac 15amp circuit does it need earth ground?
I'm guessing if I'm using a metal enclosure i would mount this directly against the metal and then it would be grounded (assuming the enclosure was properly grounded). But if my enclosure is plastic do I need to run a ground wire to the metal casing of each of these?
I would not bother. It is not common practice to my knowledge.
Weedpharma
I would use a ground connection unless professional electrical advice is to the contrary. Too much safety is rarely a problem.
It may be that your switches are "double insulated" so that there is no possibility of the high voltages coming in contact with the metal parts. But if that is the case I would expect it to be clearly stated on the switch.
I guess I just would not use metal switches. 
...R
Robin2:
I would use a ground connection unless professional electrical advice is to the contrary. Too much safety is rarely a problem.It may be that your switches are "double insulated" so that there is no possibility of the high voltages coming in contact with the metal parts. But if that is the case I would expect it to be clearly stated on the switch.
I guess I just would not use metal switches.
...R
I agree that an earth will not harm the situation and is totally safe. If the switch required an earth, it would have a tag for such a connection.
Weedpharma
weedpharma:
If the switch required an earth, it would have a tag for such a connection.
Would you risk your child's life on that statement - especially for a switch you have not actually seen ?
...R
From an unknown eBay site, probably not. But from an established reputable business possibly.
There are many brands I would not think twice about using without earthing.
As you say, if unsure, you cannot go wrong by earthing the switch.
Weedpharma
Edit
I assume however that all joints are soldered and insulated, or, use properly insulated connectors properly fitted.
Thank you all for your input.
I'll be using insulated crimp connectors on the screw terminals. I think I've now pretty much settled on a metal enclosure, the enclosure will be grounded, and I'll use rubber 'boots' for dust and moisture protection over the toggles. That should take of it... right?
weedpharma:
From an unknown eBay site, probably not. But from an established reputable business possibly.
I understand that. I was just trying to make the point that neither you nor I know exactly what switch the OP has and in that case I believe it is wise to be cautious. And also we have no knowledge of how competent the OP is to make that sort of judgment.
...R
Robin2:
we have no knowledge of how competent the OP is
Im right here, I can hear you!
theboozler:
Im right here, I can hear you!
But you are not going to tell us
...R
theboozler:
Im right here, I can hear you!
Bugga!! Forgot to engage whisper font!
Weedpharma
Of course the real issue here is that the OP has no means of knowing whether my advice is worth the steam off his ...
...R