Why can't I ground myself by touching PAINTED metal?

[Thomas-18]

I've heard you can ground yourself from esd when working on computers by touching any unpainted metal part of your computer case. But my question is that why does it need to be a UNPAINTED metal part of the computer case? I don't know what to do because every metal part of my computer case is painted black. So if I clamp the alligator clip of a anti static wrist strap to a black metal part of my computer case I'm not safe from esd? I know some of you guys are going to say things like a anti static wrist strap isn't necessary for esd safety but when working on a $1000 computer it's necessary to me. Please help.

 

[grana92]

it's because of the coating (or paint), it's not conductive. Also grounding yourself to any part of the computer is not grounding. you need to ground yourself to something else.

 

[rhysiam]

You need to touch a conductive surface (e.g. a metal surface) that is grounded. That ensures that any static charge that you've accidentally acquired from friction (or whatever) will flow through that conductive service and off to ground. I suppose if the paint is non-conductive and thick enough it'll prevent the charge from reaching the metal surface underneath.

You are massively overthinking this though. Just plug you PSU into the socket but have the socket switched off at the wall. That grounds the PSU, which by design, will then ground the case. If you're really worried about a thick painted surface, touch the outer casing on the PSU itself, or even the screws connecting the PSU to the case. They'll all be grounded and will safely remove any static charge you've built up.

 

[Phillip Corcoran]

Paint is non-conductive, so it has no earth path to discharge the static from your body.

That's why it has to be bare metal.

Scrape off some paint on the inside of the case where it won't be seen.

 

[Maarsch]

Metal is a conductor.
Most paints are isolators.

Isolators don't conduct and you might get a buildup of static electricity which might jump to your electronics
If you connect to the metal every bit of charge you build-up would flow to the case equalizing charge.

Depending on your paint, it could be electrically conductive (unlikely) or you can use your alligator clip to scratch through the paint, which I am assuming you don't want to do.

Anything else conductive (metallic) and grounded will do the job though. Work close to your central heating and connect to that. Assuming your case is uncharged (and you reconnect your PSU to a grounded socket shortly after you have moved it to your work area to ensure this is the case) nothing will spark.