They are perfect for checking phase sequence in motors, pumps, and air conditioning units. These are often called phase sequence indicators, phase rotation meters or phase sequence meters. One requirement of BS7671 is to verify that the phase sequence in multiphase (ie. three-phase) circuits is maintained. They are also used for motor and generator testing.
Three phase supplies are very common in both commercial and industrial electrical installations within the UK. They comprise of three ‘lines’ or ‘phases’, each generated 50 times per second (50Hz) by a distribution generator. Each phase winding is generated 120° out of synchronisation with each other; the sum amounting to 360° or one turn of the generator.
Three phase supplies are very economic compared to single phase supplies as they allow for higher voltages to be transmitted across the distribution network. In turn, this makes it possible for a smaller amount of material to be used for cables and switchgear within the power distribution network.
With each phase running 120° out of synchronisation, it is simple to produce a rotating magnetic field which is the key element for a motor to operate efficiently.
It is common for a three-phase supply to feed various sub-supplies which can provide power for three phase socket outlets, motors and circuits to name a few. With so many different terminations present, it is important to check that each phase is terminated correctly. As such, regulation 612.12 of BS7671 states that multiphase circuits must be verified for the correct phase sequence. A motor installed with an incorrect phase sequence could have disastrous consequences for both user safety and in the reverse operation of the motor and machinery.
Test-meter.co.uk stock a range of phase rotation meters which allow an engineer to check how the phases are rotating in relation to each other and that they are in fact connected in the correct sequence. There are two main types of phase rotation testers: the rotating disc type and the static type. Non-contact phase rotation testers are also available which enables phase rotation to be determined without the need for direct contact between the probes and live wires, which in turn allows for much safer testing.