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04/05/2005
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Dean Palmer reports on two deceptively simple design of motor starter, which should cut installation times and reduce cabinet space for panel builders and electrical engineers
 Dean Palmer reports on two deceptively simple design of motor starter, which should cut installation times and reduce cabinet space for panel builders and electrical engineers
With wiring times and effective use of cabinet and panel space a high priority for design and installation engineers, two recent developments in motor starters should help to reduce installation time and space.
The first is a two-part tool-less plug connector module that combines both electrical and mechanical connections between Moeller Electric's PKZM0 motor protective circuit breaker and a DIL M contactor. When joined, the two units form a complete MSC motor starter that offers a capacity up to 12A.
This novel connection technology delivers has several benefits. First, the mechanical element of the connector ensures a safe and stable connection of the motor-protective circuit breaker and contactor, which can be mounted on a single top-hat rail. While the electrical connector module provides the main connection of the main contacts between the two units, reducing fitting costs and eliminating wiring faults.
Another benefit is improved safety during maintenance work, where removal of the electrical connector module gives a visible isolating gap. Reversing starters using the tool-less plug technology are also available up to 5.5kW, 400V. And, where panel space is at a premium, by running across the front of the units, the interconnecting devices do not add any extra width or height to panel assemblies in the same way that other connection methods do.
The second development, which is deceptively simple but just as clever, is a simple mechanism that prevents the two contactors (in a reversing starter arrangement) switching simultaneously. By using a small ball in a special recess between the two contactor bodies, the mechanical interlock is achieved without any extra mounting space.
As one contactor moves into its 'on' position, it displaces the ball towards and slightly into the other contactor, creating a physical barrier which prevents it from switching. It seems far less complicated than other solutions currently on the market.
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Author
Tom Shelley
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