Powder Coated Metal Enclosure for Double Insulation

[dknguyen]

Is powder coating on a metal enclosure sufficient to make a device "double insulated"? Not for protection from hazardous line voltages but from ESD damage. This is a portable device and a metal enclosure is desired for shielding purposes and ease of customization.

 

[Nigel Goodwin]

Double insulated is a specific term, and powercoating would not be suitable - and I fail to see how it would help against ESD in any way?.

 

[dknguyen]

Mainly so a charge on me wouldn't get transmitted to the case which might then travel to the PCB inside through a panel-mounted device or a loose wire touching the case. If double-insualted is a specific term, then I actually just want to ask if powder coating is sufficient stop an ESD charge on me from transferring to the enclosure beneath the coating.

Or if I decide to connect the enclosure to battery ground. Not sure if that actually has any shielding benefits (whether internal or external) though or whether it would do more harm than good.

 

[Nigel Goodwin]

Mainly so a charge on me wouldn't get transmitted to the case which might then travel to the PCB inside through a panel-mounted device or a loose wire touching the case. If double-insualted is a specific term, then I actually just want to ask if powder coating is sufficient stop an ESD charge on me from transferring to the enclosure beneath the coating.

I don't see as it's a concern either way?, but ESD (if it happens) will certainly easily go through powder coating or paint.

Or if I decide to connect the enclosure to battery ground. Not sure if that actually has any shielding benefits (whether internal or external) though or whether it would do more harm than good.

If you don't connect the enclosure to battery ground it's not going to really help in anything, shielding requires it to be connected.

 

[3v0]

If painting or power coating will work depends on the insulating properties (breakdown voltage) of the material applied. A coating of corona dope would do the job but it might not make a durable surface. Powder coating is a plastic. I expect you can find one that would work too. But you need to be sure there is no path from the surface to the interior. That includes holes and where wires exit the case.

Regarding metal shielding. The high voltages seen in ESD act a bit differently. The negative battery terminal is a virtual ground. Connecting a metal shield or case to the negative terminal will not help, it is a direct path to your PCB. The case needs to be connected to an earth or some object large enough to absorb the charge.

Having said all that I expect there is little data on breakdown voltage for most powder coating or paint. There may be a paint that will do the job and you can more easily buy a can and run a test.