Effects of Vapors from Phenol Boards and Connector Lubricants on Activation of Wire Spring Relay Contacts

An unexamined trouble source for open relay contacts is addressed, i.e., that lubricants on connector systems used in the vicinity of open relays can contribute organic vapors which can cause excessive arcing behavior on the contacts. The contact activating ability of some organic connector lubricants and a phenol fiber printed wiring board have been examined. In spite of the relatively low (~10^-6Pa (1 Pa = 7.5 x 10^-3torr)) vapor pressures at room temperature, significant arc duration enhancement, and thus reduced life, was observed on palladium and palladium/silver relay contacts operating in air-lubricant gas mixtures at part per trillion levels. Operation in mixtures of lubricant wax vapor and the phenolic vapor from the boards showed an activation characteristic identical to that of the wax alone even though its concentration was approximately four orders of magnitude less than the phenol. Substantial reductions of contact life have been computed for some operating situations. A relationship between the number of carbon atoms in the activating organic molecule and the lower critical exposure for activation is observed. The larger the molecule, the lower the exposure required to activate contacts.