The simpler way to protect

Amtech’s Philip Grace suggests a better solution for protective device manufactures than a sheet of tracing paper!

It is not difficult to remember the time when protective device manufactures would use a sheet of tracing paper for each of the devices used in a circuit and to place these on top of each other to provide a rudimentary system for determining the circuit co-ordination.

That seems a long time ago yet even with advances in technology many contractors are still wary of carrying out a protection study on a circuit. This is now even more daunting with the proliferation of adjustable breakers being used these days – even on final circuits.

Clearly there are advantages to using adjustable devices as they give the designer the ability to tailor the protection characteristic to the circuit it protects. As a result it may be possible to reduce the overload setting on a protective device and reduce the required cable size accordingly.

A solution to this is to find an easy way of working with adjustable breakers. This is where advanced software packages come in as they can make the process so easy to use that you will not need to be an expert to use them. Therefore, the need to sub-contract specialist work such as protection coordination is greatly reduced.

Using software to design an electrical system is now fast and easy, plus there is the added benefit of being able to quickly amend designs if the client changes the specification.

How it works
Some packages contain large databases of protective devices, so you can select the exact device you are using, rather than ‘guessing’ with ‘generic’ devices, and simply drop it into the system. Another benefit of this is that tedious searches through catalogues are eliminated as the time current characteristic for each device that is stored in the software is supplied direct from the device manufacturer. Some packages even include manufacturers’ data sheets and graphical trip unit images.

Making protective device adjustments in the software is also easy. A very popular method is using a simple graph view of the devices in the circuit with the characteristics of each device shown on one screen alongside each other. This method allows overload, short circuit, instantaneous and earth fault settings to be changed simply by increasing or decreasing the values on screen until the co-ordination is acceptable. This is reflected instantly on screen.

In fact, some software will automatically determine the overload settings depending on the design current in the circuit.

The role of this type of software is to help turn complex, time consuming tasks into simple and far more intuitive processes. This includes validating adjustable breakers in seconds with complete confidence that your calculations are accurate. However, there are other benefits – not only can the time current discrimination be shown visually on screen, the whole circuit can also be checked instantly at the touch of a button, thus saving time and giving users more confidence in their designs.

This works by designing projects in the usual way, typically building a schematic by selecting symbols from the on-screen library and dragging them into the project on screen. The software contains a large database of cables, busbars and protective devices so these can be easily selected and added instantly to the project. A big advantage is that the specifications of these components are often supplied from the manufacturers, so the information is up to date, accurate and, very importantly, specific to that device. This means you will be using the exact details for each component rather than using generic devices.

Error correction
Following the design process the next step is to click the ‘Discrimination Check’ button. Then the software goes through the design and automatically checks the discrimination. If an overlap is found the software displays an error message(s). When you click on one of the error messages you are taken directly to the relevant part of the graph so you can see instantly where the error is and can rectify it in seconds.

It’s probably true to say that this type of software is one of the overlooked heroes of the electrical world. Even people using design software are often unaware of some of the capabilities it offers. This software also offers opportunities for companies who are currently ‘farming’ this type of work out because they either do not have the time or expertise. The software takes the mystique out of electrical discrimination but with the advantage of accurate results, giving you complete confidence to do this work in-house.

For more information visit the Amtech website or call us on 0800 028 28 28.

Article originally appeared in Electrical Engineering, July/August 2012 issue