What has surge protection got to do with safety?

Written by Mark Lloyd and Andy Maskell

Anything that increases the reliability of your safety circuit has to be a good thing…..

In fact, it is a basic requirement when using safety relays or Safe PLCs that the outputs are protected against overcurrent and overvoltage to prevent dangerous failures.

In the case of a safety relay output, this may be in the form of a welded relay contact for example.

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So wouldn’t it make sense to fit SURGE PROTECTION?

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If you are considering CCF or Common Cause Failure in a dual channel system Table F.1 in ISO 13849-1 (See below) demonstrates the measures you can use to reduce the likelihood of these failures occurring.

The table provides a scoring system relating to the how well this has been done using the engineering methods listed in the table. These measures increase the integrity of your safety control circuit and safety in general. One of the measures is to provide protection against overvoltage, overpressure, overcurrent and over temperature.

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A score of 75 is deemed to satisfy this requirement and forms an essential part of the safety design and implementation. Fitting surge protection gives you a 15 point contribution towards this score and is the third highest on the list.

So hopefully the message is clear…

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