IEC 60172:2015 specifies, in accordance with the provisions of IEC 60216-1, a method for evaluating the temperature index of enamelled wire, varnished or unvarnished with an impregnating agent, and of tape wrapped round and rectangular wire, in air at atmospheric pressure by periodically monitoring changes in response to AC proof voltage tests. This procedure does not apply to fibre-insulated wire or wire covered with tapes containing inorganic fibres. This fourth edition cancels and replaces the third edition published in 1987, Amendment 1:1997 and Amendment 2:2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - Revision of Clause 1, Scope, to incorporate appropriate text from former Clause 2, Object; - Deletion of Clause 2, Object, by placement of its text into existing clauses; - New Clause 2, Normative references; - Revision of 5.1.1, 5.3 and 5.4 with corrections to Amendment 2 to the third edition; - Revision of Clause 7 as to clarify which specimens comply with Table 3 and Table 4; - Revision of figures with high-resolution photos and graphs. Keywords: enamelled wire, tape wrapped round and rectangular wire, AC proof voltage tests