Electric motors

There are various applications for electric motors such as boreholes, irrigation and swimming pool pumps, security gates and garage doors. Borehole and irrigation motors are supplied as three phase (380-400V) or single phase units (220-230V) and require special starting and control equipment. It is not advisable to supply them via only a circuit breaker directly from the power supply, as this does not provide adequate protection for the electric motor. Borehole pump motors burn out very quickly if they are not cooled down by the water being pumped from the borehole.

Special protection in the form of a “phase angle relay” have to be installed to suit the particular motor and pumping characteristics to guard against this “dry running” condition. It is always better to have a borehole pump pumping to a static local on such as a storage tank (fixed back pressure and head of water) than directly to an irrigation system, where the back pressure and head can change due to different sprinklers and taps being opened. As the phase angle relay could see this as a fault and nuisance tripping of the pump would occur.

Various types of borehole starter panels are available for different applications, and it is best to contact a supplier of these panels when planning to install a system. Irrigation or booster pumps also require special control panels to protect the electric motor and also, if necessary, damage done by pipe bursts or blockages. They can be manufactured with various types of control systems such as float switch, liquid level, irrigation controller, time switch, pressure switch, flow switch, etc.

Again, check with a control panel supplier when planning your system and seek their help for the best possible options. Swimming pool pump motors are normally single phase and controlled from a purpose made “pool box”, which is available off the shelf in various formats, i.e. weatherproof, with circuits for low voltage pool lights, 15A domestic socket outlets, etc.

Spa baths also require a special control box to not only control the pump motor, but also the heating elements. These units, again, are available as off the shelf items in various formats. Control panels for gate motors and garage doors are also available as off the shelf units, in various formats depending on the type of gates and doors installed.

While 220/230V AC motors are available for these applications, it is always advisable to use low voltage DC motors so that the onboard battery in the control panel will still operate the gates and doors during a power failure.

Information supplied by Buildaid Publishing.

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