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Not long ago, choosing the best type of starter to use in a control panel was easy, mainly because there was practically no choice! Now however, there’s a bewildering array of options.

A traditional motor starter for use in a control panel is made up of three fuses, a contactor and an overload with variations on this theme for reversing, star-delta and other more specialised starter types. Starters based on this apparently simple arrangement are still widely used, even in new equipment.

There’s nothing wrong with this, especially as this arrangement often involves the lowest expenditure on starter components. It’s worth noting however, that this doesn’t necessarily mean the lowest cost per starter – the traditional design has a lot of components to be mounted and involves a great deal of wiring. The resulting labour costs can easily outweigh the savings on hardware.

Traditional starters also have a number of shortcomings that may not be immediately obvious. For example, any modern starter should be expected to provide Type 2 protection co-ordination, as defined in BS EN 60947-4-1. Traditional starters can do this, but only if the components are properly chosen.

Control gear manufacturers provide excellent guidance on component choice, but it’s all too simple to substitute, for example, fuses of the appropriate rating but of the wrong type. This is a particular risk if blown fuses need to be replaced when the equipment is in service. Plus, fitting the wrong fuse can seriously compromise safety.

Even the actual use of fuses can be problematic. If a fault occurs, and there are no replacement fuses to hand, the result can easily be a substantial period of costly plant downtime while spares are being obtained.

An attractive alternative to the traditional starter is a version that uses just two components – a motor protection circuit breaker and a contactor. The motor protection circuit breaker combines short circuit and overload protection in a single device, entirely eliminating the need for fuses. Often, it also provides facilities for isolation. Now there are only two components at most to mount and wire, resulting in significant savings in labour costs.

Furthermore, now the designer only has to select the right contactor to go with the circuit breaker and Type 2 co-ordination is guaranteed. Let’s just take a moment to review what this means. Type 2 co-ordination requires that the starter will behave safely under fault conditions, but it goes further than this. It also requires that no damage will be caused to the starter by a fault, with the exception that a little light welding of contacts is permissible.

In other words, after an inspection to check for welding and the breaking of the welds if this is necessary, the starter will be fit for immediate return to service. Since no parts have to be replaced, the possibility of fitting the wrong components, which is always present with fuse-based starters, is completely eliminated. In addition, there’s no risk of the required components being out of stock, because none are needed. The end result is that when two-component starters are used downtime after a fault is kept to a minimum. This is a highly desirable situation in business today, when plant outages often cost tens of thousands of pounds per hour.

Some control gear suppliers take the two-component starter idea a step further by providing motor starter combinations where the breaker and contactor connect together directly without the need for any wiring at all. Not only does this save even more wiring time, it also produces a single unit starter which can be mounted simply by clipping it to a DIN rail.

A further benefit of this close-coupled approach is that it is virtually impossible, if a breaker is damaged, to fit a replacement of the wrong type.

The starters we have considered so far have all been individual units that require their own power and control connections, but there are new products available that adopt a better approach.

New starters can be used with three-phase commoning links that eliminate most power wiring, or they can be used in conjunction with busbar adaptors that let them clip directly on to standard-sized busbars. Both options cut wiring time and reduce panel space requirements, hence saving money.

On the control wiring front, there are even more exciting developments with the introduction of fieldbus systems that have been optimised for use inside the control panel. They are simple to implement – the necessary interface modules clip on to the starters just like ordinary auxiliary contact blocks. With these modules in place, the starters are connected to the system’s PLC with the aid of a plug-in daisy-chain ribbon cable. Addressing is automatic, so no specialist knowledge is needed.

Even in large panels, making the control connections takes just a few minutes, compared to the hours that are often needed for conventional wiring. Another major benefit is that, just like conventional fieldbus systems, such units eliminate the need for PLC I/O modules to handle the individual signals from the connected devices. As well as saving on the cost of these modules, this also means that a smaller PLC can often be used, yielding more savings.

Taken together, in most applications these cost savings easily outweigh the extra expenditure on interface modules, making the in-panel fieldbus a very attractive option financially. It’s also got a lot to offer on the technical front, as the use of plug-in connections virtually eliminates the risk of wiring errors and produces a system which is easy to modify should the user’s needs change.

So, let’s try to answer the obvious question – what’s the best type of starter to use? It depends of course on the application, but in many cases the best choice is likely to be the two-component starter, made up of an overload and a motor protection relay. Starters of this type are easy to specify and use, they’re competitively priced, offer high levels of safety and are available in a wide range of ratings.

Starters with fieldbus-style control wiring systems are likely to be an even better choice for PLC-based systems, especially when a particularly compact panel is needed, or the ability to reconfigure the control system quickly, easily and economically is important. As we’ve seen, this type of starter may be a little more expensive than its more conventional counterparts, as each one needs an interface module. The extra cost is, however, offset by the savings offered in other areas.

Finally, what about the good old fuse, overload and contactor starter? As stated earlier, there is nothing actually wrong with this arrangement but it has limited appeal when compared with more modern alternatives. It perhaps has a place in simple systems where the lowest possible component cost is essential, but it’s becoming hard to justify its use elsewhere.

There’s no doubt that motor starting has changed in recent years, but only for the better. Designers have more choice than ever before, allowing them to match their motor starting solutions to the exact technical and budgetary requirements of the application in hand.