The Surge

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How do you  prevent and electrical surge or spike from damaging your equipment? As a new transmitter is being planned for one station there seems to be some disagreement on what method or type of suppressor is best. It looks like the two main types are Series and Parallel protection.

I have been reading some literature  on the subject from the IEEE and Emerson. The differences seem to boil down to this – For total protection from noise and spikes Series protection is best as it can track the waveform and suppress spikes that occur anywhere along it’s rise and fall in voltage as well as removing any noise that is also riding on the sine wave. But if the Series protection is not designed well damage to the SPD (Surge Protection Device) can lead to smoke, fire and even explosion of some metal-oxide varistor based systems. One engineer told the story of a new Series SPD being powered on the first time and it’s door was blown off and across the parking lot. It seems the manufacture had mislabeled and installed 120V MOVs on a 480V system.

On the other hand Parallel SPDs merely attach across the power lines and only provide a suppression of voltage spikes over the peak

Series SPD (Click to Enlarge)

AC waveform voltage and it’s filters seem to be much more limited in bandwidth than the Series SPDs. But failure of a Parallel SPD will likely not result in loss of power, just loss of protection. These are easier to install and can be done with power left on.

Parallel SPD

The IEEE paper I referred to is called “The Emerald Book: IEEE Recommended Practice for Powering and Grounding Electronic Equipment”. You can get it from them for $180 or if your a member it’s only $144, click here to get it from IEEE.

I did find an older copy  from 1999 online, someone had posted, it’s very interesting, you can find that one here.