This Recommendation sets terms@ test methods@ test circuits@ measurement procedures and preferred result values for the surge parameters of isolating transformers used in telecommunication devices and equipment. Three types of isolating transformer are covered: mains@ switched mode power supply and signal. The surge parameters of the isolating transformer insulation barrier covered by this Recommendation are: rated impulse voltage input winding to output winding capacitance insulation resistance. Additional parameters for signal isolating transformers are: core saturation voltage-time product rated input winding root mean square (rms) current for a given temperature rise. This Recommendation does not cover the transformer parameters required to help ensure appropriate operation on the service e.g.@ signal transformer return loss.