IE6: Belt drives

Hazards: Power transmission belts can become electrostatically charged because of the constant separation of contact surfaces.

Protective measures: Alternative drive concept using gears, chains or similar. Use conductive power transmission belts.

This cause of electrostatic discharges is an operational ignition source because of the constant separation of the contact surfaces. It is consequently essential in this case to put protective measures in place when used in Zone 2 onwards.

The agitation devices in standard commercially available mixing machines are chain-driven, so no electrostatic charging is likely in this case.

By contrast, belt drives are sometimes used on conveyors working in conjunction with continuous-flow driers. Belt drives are also used to move automatic application units.

A build-up of charges is likely when operating such belts as a result of the continuous separation of two surfaces in contact with each other in the form of the belt pulley and the belt. The charge can be considerable, meaning that there is the risk of ignition in the event of a discharge.

The fundamental permissibility of belt drives depends on the probability of an ignitable atmosphere occurring.

Their use in Zone 0 is always inadmissible, while the use of conductive earthed belt drives is possible in Zone 1 or Zone 2 on condition that a belt speed of 30 m/s is not exceeded and, at the same time, the product of the resistance of the power transmission belt (R), measured in the centre between the pulleys, and the belt width, or double the flank width (B) in the case of V-belts, is ≤ 10⁵ Ω m. Multi-ply flat belts, on the other hand, may not exceed a volume resistance of 10⁹ Ω to IEC 93 under standard atmospheric conditions, i.e. 23°C and 50% relative humidity.

	Example: Operation of automatic application system with belt drive
	Example: Fan in ventilation unit