IEC 62621:2011 specifies characteristics for composite insulators of electric traction overhead contact line systems for railways, as defined in IEC 60913. Insulators specified in this standard are applied for electric traction supply voltages with a nominal voltage greater than 1 000 V for a.c. or a nominal voltage greater than 1 500 V for d.c.. The standard establishes the product characteristics, the test methods and acceptance criteria.