These distances are influenced by voltage level, pollution degree, and the system insulation category. The IEC 61439-1 standard is the most commonly used document for defining these values. It applies to low-voltage switchgear and control gear assemblies and provides a table of. The IEC standard for busbar clearance plays a critical role in the design and safety of electrical panels and power distribution systems. Adhering to industry standards such as IEC 61439(low-voltage switchgear and controlgear) and UL 891(switchboards) enhances. Guide to Low Voltage Busbar Trunking Systems Verified to BS EN 61439-6 Guide to Low Voltage Busbar Trunking Systems Verified to BS EN 61439-6 November 2014 Guide to Low Voltage Busbar Trunking Systems Verified to BS EN 61439-6 Companies involved in the preparation of this Guide Acknowledgements. The first is clearance, or the distance through air between conductors of opposite polarity or between an energized conductor and ground. The distances are measured from metal to metal, and vary with voltage and also with. Circuitry connected to a DC MAINS SUPPLY is considered to be a SECONDARY CIRCUIT (for example, an SELV CIRCUIT, a TNV CIRCUIT or a HAZARDOUS VOLTAGE SECONDARY CIRCUIT) in the meaning of this standard. NOTE : See ITU-T Recommendation K. 27 for bonding configurations and earthing inside a. And for general industrial control equipment, voltage range 301-600, shortest distance is shown as 1/2" with this same value being shown through oil or air over surface. Between live parts of opposite polarity, 251-600V, Through air gap is 1", Over surface is 2".