Written by Mark Lloyd, Senior Product Manager- Power Supplies & Surge Protection
In the relatively short amount of time I have been involved with the “Dark Arts” that is surge protection, one of the main misconceptions is that a SPD is a kind of fuse that acts once and then needs to be replaced. This is not true. The SPD acts more like a valve that only conducts when a transient overvoltage rises to a certain level, at which point it conducts to earth and limits the voltage the load sees, therefore protecting it. So a SPD is good for multiple transient events- however, the semiconductor components within SPDs will eventually wear out and unless there are regular visual checks or there is feedback to the system in the form of a remote contact, then potentially the SPD will not be doing its job.
Unlike overcurrent protective devices such as a fuse or MCB which sit in line and when they do their job and trip shut down the load, a SPD sits across conductors and takes no active part in the application. So when there is a transient event the SPD will protect the downstream loads but not interrupt them. In truth, this was always a difficult product to sell because when it is doing its job, the customer does not necessarily know it has operated.
Given the above, my advice is always that SPDs should not just be installed and then forgotten about.
At the very least installers should make use of the remote contact which will provide feedback that the SPD has “failed”. Most reputable SPD manufacturers will have a thermal disconnection mechanism that operates when the varistor reaches a critical temperature at which point it mechanically takes the varistor out of circuit. At this point the SPD is not providing any protection.
More than this, IEC 62305-3 a part of the international standard for lightning protection, states that surge protective devices must be tested regularly. The table below shows the recommended intervals for different lightning protection levels.
In addition, the standard requires the traceable documentation of test values- but I can tell you from my short experience, there are not many end users that do this regular testing.
What can Phoenix Contact offer that would be of use in this respect?
Virtually all of our SPDs have the surge protection circuitry housed in removable plugs and these plugs can be tested with a piece of kit called the Checkmaster 2. This allows the user to test the status of the device, save the results and download in the form of a CSV file with a simple memory stick. From this you can produce a report together with dates and times giving a record for evidence that the routine testing has been carried out.
So, the Checkmaster 2 is very useful for testing the functionality of your SPDs, but what if you want to monitor their performance in real time?
Released last year, the ImpulseCheck is a cloud based monitoring device that records any transient events, whether caused by lightning or electrical switching, and stores this time stamped information in the cloud. It also acquires the status (state-of-health) of any Phoenix Contact surge protective devices being monitored and a corresponding report can be generated at any time with the push of a button.