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I've bought some high power electronics with some sensitive components. Since they are just bare boards straight from the manufacturer, I have constructed a perspex surround with fans facing the underside of the board. The manufacturer warns that they should be used in a static free environment. I wouldn't normally be concerned, but its a lot of moneys worth of gear.

Plastic is a 'magnet' for dust and grease and builds up plenty of static, especially when there are moving parts (the fans?). My rookie question is how do I prevent any build up of charge?

If I strapped aluminium tape to the side of the plastic case and wired a connected cable to the mains ground, would this help? The case is held together with nylon hex spacers, should I ground all sections of the perspex?

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Aluminium (or better yet, copper) tape is a good way of shorting out any charge build-up on the perspex case. It is also a great way to create a short circuit and fry all your electronics inside the case.

I have seen plastic cases with ESD-sensitive electronics inside, protected by a thin layer of electronics protection type conducting foam on the inside. This is generally only on the underside of the board, which is likely to come into contact with the plastic case. This foam is the type that ICs are sometimes shipped in, dark gray or black and very... foamy. Resistance is high, of the order of several Megaohms per centimeter, but that works fine.

Another more home-grown alternative, is to cut up and use a metallized shielding plastic bag, the type with a wee bit of conductivity courtesy a thin layer of conductive material sandwiched between layers of plastic. These bags are often semi-transparent, so you'd retain the ability to peek into the case, as the perspex probably lets you do. Again, some vendors ship electronics in such bags.

Using either of these two approaches will not create a Faraday cage, nor will they entirely eliminate static charge build-up. What they will do is distribute such charge across the foam / plastic, thus spreading the risk, so to speak, and reducing the chances of a very high charge build-up.

Note that ESD protection bags look similar, but without the metallic shine, and are not equivalent to metallized plastic. Those will not be useful in this context.

For more information on the metallized bags and ESD bags, see this answer to another question: "Do antistatic bags have conductive interior, exterior or both?".

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  • \$\begingroup\$ Is the pink foam acceptable as well? \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 2 '13 at 18:35
  • \$\begingroup\$ @IgnacioVazquez-Abrams I haven't ever seen pink conducting foam, so I can't say what you are referring to. :-) \$\endgroup\$ – Anindo Ghosh Sep 2 '13 at 18:37
  • \$\begingroup\$ @IgnacioVazquez-Abrams The Pink-Poly anti-static stuff, commonly made into bags, bubble wrap, and foam is not conductive. In my opinion, it is almost worthless for ESD. The pink poly won't generate static on it's own, but it also won't protect or dissipate the static. Many times I've put a device into a pink poly bag and zapped it with static through the bag. The metallic silver stuff, or the solid black things (conductive carbon) are good. \$\endgroup\$ – user3624 Sep 2 '13 at 18:42
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Here's an "outside the box" suggestion: Build the enclosure out of wood instead of perspex. Wood does not build up static electricity, and also does not short out electronics when in contact.

Another option is to coat the electronics in a conformal coating, such as acrylic spray. Make sure you get a full, even coverage, and then you can use sheet metal for the enclosure without too much worry of shorting things out.

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  • \$\begingroup\$ This is ultimately what I did, albeit for different reasons (remade the enclosure out of wood). Worked out fine. However, In reflection my concerns were massively blown out of proportion, especially given the circuitry was built to handle typical loads of 40A DC. The price tag and manufacturer's warning got the better of me. \$\endgroup\$ – rom Oct 18 '13 at 20:59

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