Electricity + Control April 2019

ELECTRICAL PROTECTION + SAFETY

Understanding the terminology in IEC 61439

By Johan Basson, Managing Director, JB Switch- gear Solutions (Pty) Limited

air does not exceed 50% at a maximum of +40°C. Higher relative humidity may be permitted at lower temperatures, for example 90% at +20°C. Moder- ate condensation, which may occasionally occur due to variations in temperature, should be kept in mind. For outdoor installations, the relative humidity may be temporarily as high as 100% at a maxi- mum temperature of +25°C. 1.1.3 Pollution degree This topic is addressed comprehensively in the second part of this tutorial. 1.1.4 Altitude The altitude of the installation site will not exceed 2 000 m. For equipment to be used at higher al- titudes, it is necessary to take into account the reduction of the dielectric strength, the switching capability of the devices and the cooling effect of the air. 1.2 Special service conditions Where any special service conditions exist, the particular requirement applicable to the special condition shall be complied with, or special agree- The IEC 61439 series of standards is appli- cable to low voltage switchgear and con- trolgear assemblies. Johan Basson looks at some of the terminologies and explains them so that the reader may gain better understanding of their meaning. Extracts from the standard itself are used exten- sively.

1. Specific service condi- tions apply to ensure the safety and efficiency of electrical assemblies in industrial applications. Take Note! 1

IEC 61439 standards are applicable to low voltage switchgear and controlgear assemblies.

T his tutorial looks at ‘service conditions’ in which electrical assemblies may be used and, in the second part, focuses on degrees of pollution considered in these service conditions.

1. Service conditions

1.1 Normal service conditions What is regarded as ‘normal’ in the standard? If components are used which are not suitable for these conditions, appropriate steps should be tak- en to ensure proper operation. 1.1.1 Ambient air temperature For indoor installations, the ambient air tempera- ture does not exceed +40°C and its average over a 24-hour period does not exceed +35°C. The lower limit of the ambient air temperature is -5°C. For outdoor installations, the ambient air tem- perature does not exceed +40°C and its average over a 24-hour period does not exceed +35°C. The lower limit of the ambient air temperature is -25°C.

1.1.2 Humidity conditions For indoor installations, the relative humidity of the

12 Electricity + Control

APRIL 2019