High voltage disconnecting switches are assigned certain ratings and standard tests are conducted to assure the user that the switch when new, will perform within the rating shown on the nameplate. It should be recognized that the switch in service will perform within these ratings only if properly operated and maintained. It cannot be stressed too strongly that prescribed safety rules should be adhered to at all times when operating or maintaining high voltage disconnecting switches near energized equipment or conductors.
High Voltage disconnecting switches, grounding switches, and horn gap switches are given no interrupting rating .* The following general rules should be followed:
Prior to operating, check to see that it is fully closed and latched or fully open, as intended. Switches should be closed rapidly.
After operating a switch, check to see that it is fully closed and latched or fully open, as intended. Do not use undue force in attempting to operate a switch. The operating mechanism is designed properly for the switch and any undue force, in the nature of an extension of the operating handle, an extra person on the operating handle or switch stick, may cause severe damage to the switch or mechanism. A few sharp raps on the vertical operating pipe or suddenly applied tugs on the operating handle may help to free an iced switch mechanism.
Power-operated switches should be operated periodically to ensure that the switches and their mechanism and control features are functioning properly. Where the circuit conditions will not permit operating the switch energized and the circuit cannot be de-energized for this purpose, it is suggested that arrangements be made to disengage the operating mechanism from the linkage to allow the control circuits and mechanisms to be checked, provided that this method does not adversely affect the over-all adjustment.
* It is common practice to use these devices to interrupt small values of current such as the charging current of a short length of transmission or distribution line, transformer magnetizing current, or light load current. It should be recognized that such operation results in unconfined electric arcs at the switch contacts which under unfavorable conditions may cause damage to the switch, and which may involve adjacent phase conductors or supporting structure in the initiation of system faults. Transfer switching in parallel or loop circuits also has the same attendant hazards. If current interruption is contemplated, care should be taken to be sure that the current magnitude is in a range that can be handled by the switch with a good probability of successful interruption.
"Interrupting Ability of Horngap Switches." American Institute of Electrical Engineers Transactions, vol. 69, 1950, part II, pp. 1016-1027.
"Transformer Magnetizing Current and Its Effect on Relaying and Air Break Switch Operation." AIEE Transactions, vol. 70, 1951, part II, pp. 1733-1740.