The silicone gasket around the door or access panel of an electrical enclosure has two jobs. Not only does it keep dust out, but it also keeps electrical noise in. Or it does if made from the right material.
The Noise Problem
Electrical noise, sometimes called electromagnetic interference (EMI) or radio frequency interference (RFI) is a problem in some environments. By interfering with wireless transmissions EMI makes phone calls difficult and disrupts wireless data transmission. It can also induce currents in other conductive materials. That can lead to spurious data signals, possibly giving rise to false alarms or affecting process control equipment.
Conversely, sometimes sensitive electrical equipment needs shielding from environmental EMI. Placing it in a metal enclosure keeps the EMI outside, avoiding problems of signal interference.
EMI Sources
EMI travels through air, spreading out from a source much like ripples on a pond. Circuit breakers, relays, transformers and switches can all produce EMI. This is one reason they’re often placed in an enclosure. Motors, power cables and welding equipment also produce EMI, but aren’t so easily shielded. However, sensitive electronics near these items may need to go in an enclosure.
Conductive Shielding
When waves of EMI meet a conductive material the energy spreads out over the surface rather than continuing on. Gaskets and flanges however provide an opportunity for leakage.
With most enclosures, closing the door leaves an uneven gap. That could allow dust inside, which is the main reason a gasket is fitted around the opening. Electrical enclosures are usually sealed with silicone gaskets, which offer good compression and stand up to elevated temperatures. However, silicone is not naturally electrically conductive. That results in a leak path where EMI can escape.
Ask for Electrically-Conductive Gasket Material
When replacing gaskets around an electrical enclosure, or specifying new, always consider the need for EMI shielding. Electrically-conductive gasket materials are available, but it’s important this issue is raised when speaking with the material supplier. In many cases conventional silicone gasket material will be sufficient, but if EMI could be a concern, let your vendor know.