Tips on Applying Relays
15.5 Environmental Considerations
Relays are applied in a wide range of environments ranging from office
equipment to earth-moving equipment. It is important that the selected relay
be capable of functioning in the application environment. Such factors are
humidity, salt spray, water spray, extreme heat, extreme cold, shock,
vibration, corrosive atmospheres, large stray magnetic fields, rapid thermal
transition, and chemical exposure can influence relay performance. Where
possible, the manufacturer should be provided with a specification defining
the possible environmental factors of the application.
15.5.1
One environmental combination that has often created application problems is
the use of silicone based oils or sealing compounds with open or dust-covered
relays where light to moderate contact arcing occurs. Silicone compounds will
creep over long distance and can generate vapors at high ambient temperatures
that lead to potential relay failures. The arcing during opening of the
contacts can cause the silicone to decompose and deposit small areas of
silicon dioxide near the mating site. This deposition can increase with
operations and eventually will result in contact failure to make. The
conditions for silicon dioxide growth have been studied in numerous
experiments since the late 1960s with varied results. Type of load, ambient
temperature, and cure level of the silicone are some of the more significant
factors.
Reference: SAE ARP 4005 on precautions in applications. Frank J. Oliver
(Hayden) "Practical Relay Circuits."