The European edition of the general requirements for substation automation equipment is applied to the protection, control and communication devices installed in high voltage substations, an environment that combines continuous duty with unusually severe electrical disturbance. European transmission and distribution operators specify equipment against this standard because the alternative, relying on the ordinary industrial immunity levels, does not reflect what happens in a substation when a disconnector operates, when a fault current flows or when the station is struck by lightning. The standard sets requirements for the ambient temperature and humidity range, for mechanical and seismic conditions and for the power supply drawn from the station battery, and it defines a complete set of electromagnetic compatibility requirements whose immunity levels are increased above those of the basic publications. It is an equipment standard and not a protocol standard, and it is applied alongside the protocol parts of the same series that govern how the devices exchange information.