Very low frequency.  This is generally a voltage source used in testing insulation quality.  The power source frequency may range from 0.01 Hz to 60 Hz.

Delivering Powerful Reliability Solutions

 Abbreviation for alternating current.

 Electrical current that periodically reverses direction, usually several times per second.

 The measurement unit for electrical current.

 Abbreviation for Automatic Transfer Switch.

 A switch that automatically transfers electrical loads to alternate  or emergency-standby power sources.

 Time during which the UPS can supply the rated load with nominal-quality power while the normal source of power is unavailable. This time depends on the battery and the efficiency of the UPS. Typical backup times range from five minutes to several hours.

 Battery cell installation system whereby the cells are placed on several vertically stacked shelves or racks.

 Battery with a gas recombination rate at least equal to 95%, so that no water need be added over battery life, usually called "maintenance free."