2.7 - Undervoltage

This chapter of the Regulations deals with the prevention of dangers that could occur if voltage falls to a level too low for safe operation of plant and protective devices. Another problem covered is the danger that may arise when voltage is suddenly restored to a system which has previously been on a lower voltage or without voltage at all. For example, a machine which has stopped due to voltage falling to a low level may be dangerous if it restarts suddenly and unexpectedly when full voltage returns. A motor starter with built-in undervoltage protection will be explained in {7.15.1}.

The attention of the installer and the designer is drawn to the possibility that low voltage may cause equipment damage. Should such damage occur, it must not cause danger. Where equipment is capable of operating safely at low voltage for a short time, a time delay may be used to prevent switching off at once when under-voltage occurs. This system may prevent plant stoppages due to very short time voltage failures. However, such a delay must not prevent the immediate operation of protective systems.