The etiology of loosened connections in hospital-grade plugs

The loosening of terminal connections over time in wired, hospital-grade plugs has been reported. This study was performed to determine the extent of the problem and the cause(s) of the loosening connections. Of 45 hospitals responding to the survey, 15 reported a total of 25 melted plugs. Terminal torques were measured on the plugs of ninety-nine randoMly selected medical devices; 21% of the inspected torques measured zero in-lbs. Static mechanical tests were performed on the plug terminals of five manufacturers. A maximum decrease in torque of 18% was noted over a 6-month period. The combined affects of current cycling and cold flow on the terminal torques were also noted to be about 43% over a six-month period. Loosening torques appear to be more frequently associated with appliances requiring high currents and those that are frequently inserted and withdrawn from receptacles. It is concluded that a serious problem exists with loosened terminals in hospital-grade plugs. Until a design change can correct this screw loosening, maintenance groups have a responsibility to assure adequately low wire-to-terminal resistances. A semi-annual torquing of the plug connections of critical function medical devices should be considered.