IEC 60331-21:1999标准适用于额定电压为0.6/1.0 kV及以下的电缆，包括单芯和多芯电缆。该标准规定了电缆在火灾条件下的测试程序和要求，以确保电缆在火灾条件下的电路完整性。测试包括在一定的温度下进行的电缆电路完整性测试和电缆电路完整性持续时间测试。

在测试过程中，电缆应按照其设计和安装要求进行安装，并应在标准规定的温度下进行测试。测试应在实验室或现场进行，测试结果应记录并报告。

IEC 60331-21:1999标准的目的是确保电缆在火灾条件下的电路完整性，以保护人员和财产免受火灾的危害。该标准的实施可以帮助电缆制造商和用户选择合适的电缆，并确保电缆在火灾条件下的性能符合要求。

相关标准
- IEC 60331-1:1999 Tests for electric cables under fire conditions - Circuit integrity - Part 1: Test method for fire with shock at a temperature of at least 830 °C for cables of rated voltage up to and including 0,6/1,0 kV and with an overall diameter exceeding 20 mm
- IEC 60331-2:1999 Tests for electric cables under fire conditions - Circuit integrity - Part 2: Test method for fire with shock at a temperature of at least 830 °C for cables of rated voltage up to and including 0,6/1,0 kV and with an overall diameter not exceeding 20 mm
- IEC 60331-11:1999 Tests for electric cables under fire conditions - Circuit integrity - Part 11: Apparatus - Fire with shock
- IEC 60331-23:1999 Tests for electric cables under fire conditions - Circuit integrity - Part 23: Test for unprotected small cables for use in emergency circuits
- IEC 60331-25:1999 Tests for electric cables under fire conditions - Circuit integrity - Part 25: Procedures and requirements - Cables of rated voltage up to and including 0,6/1,0 kV