EngineerIT Inbox July 2014

July 16th, 2014, Published in Articles: EngineerIT


Readers engage in a spirited debate on the pros and cons of surge arrestors.

Winning letter to the editor

No protection from used-up arresters

Dear Editor

In the news item entitled “No protection from used-up arresters” on page 35 of the June 2014 issue of EngineerIT magazine, Jonathan Palmer of Powerman makes the statement about surge arrestors being worthless in order to promote his own surge protection product – the so called AIM product – which he says has additional functionality to a conventional surge arrestor.

I contest his statement that a surge arrestor functions like a sponge, which when it is full does not function. This is a load of crap. A surge arrestor does not absorb any energy – it is merely manufactured of material that has the ability to conduct current to earth at high speed, thus causing a diversion path for the current to flow to earth, and preventing it from passing through the device that is being protected. This is achieved in various ways with different technologies.

I request that the statement made about surge arrestors working as sponges be corrected. When a surge arrestor functions under normal circumstances it acts as a high speed switch that causes diversion as mentioned above.

A surge arrestor may have a limited life after switching high currents, due to the degrading properties of, for example, the material in a MOV. This may cause the surge arresting device to fail and the arrester would then need to be replaced. However, the arrester cannot be regarded as having the properties of a water-logged sponge.

The product item by Powerman leads one to believe that a surge arrestor has no function as a protective device in the industry, and I have a problem with this.

Could we please get clarity on what makes Mr. Palmer’s product so much better than a conventional surge protection device, and also the IEC tests and results to which the AIM product has been subjected to support the claim that it is superior to conventional surge protection devices.

Chris Coetzee, SmithsPower


Response from Jonathan Palmer, Powerman

Dear Editor

I thank Mr. Coetzee for his input. Most people have little understanding of the technicalities of surge protection, so when writing a one paragraph news item I tried to clarify the concept of the life of surge protection devices through an analogy. Becoming highly technical is not possible in one paragraph, and for those who are technical and require more information, contact details are provided.

We most certainly are not knocking surge protectors – we are just saying that our AIM product offers additional protection and functionality by disconnecting the load if and when the surge arresters fail or no longer function. In other words, a secondary stage of protection is provided.

Surge protectors have a huge role in South Africa and will continue to do so, but how often does one get to notice that the fault indicator on a surge protection device (SPD) is displayed? This would mean that the SPD is no longer providing protection, yet the power remains connected. So what is the point of that?

Most end-users buying a surge protector think that it will last forever, and they are genuinely unaware that these units may fail after excessive surges, or after diverting too many surges. Often the companies that sell them do not explain this fact. But if you look at the specifications of MOVs it tells you exactly how much energy can be absorbed, before the end of their life.

My sponge analogy (a sponge absorbing water rather than energy) tried to help users realise that surge protectors have a limited energy absorbtion capability, after which they need to be replaced. To quote from Circuits Today ( with regard to MOVs (

“The only problem with this component is that they cannot withstand the transient voltage more than the exceeded rating. They tend to deteriorate after a certain level. If so, they will have to be replaced at times. When they absorb the transient voltage they tend to dissipate it as heat. When this process continues repetitively for some time, the device begins to wear out due to the excessive heat.”
Of course this is also a simplified explanation, but for those out there that are more technical we will gladly assist.

Jonathan Palmer, Powerman

Note by investigative editor, Chris Yelland CEng:

I was asked to investigate the complaints by Chris Coetzee about an article in EngineerIT as detailed above.

Firstly, the article in question was a one-paragraph product news item and not a technical article. Secondly, Mr. Palmer did not say that traditional surge protection devices were “worthless”, but that they provided “limited” protection. Thirdly, it is not correct for Mr. Coetzee to say that “a surge arrestor does not absorb any energy”. On the contrary MOV (and other) surge arresters do absorb energy in the process of diverting surge currents to earth, and indeed have a finite and cumulative energy absorbtion capability, after which their characteristics (such as leakage current under normal operating conditions) change, leading to thermal runaway and failure.

While disconnecting my mother-in-law’s heart/lung machine when the associated surge protection device fails, may not be considered the right approach, other less critical surge protection applications (like my home PC and router) may certainly benefit by being disconnected when the associated surge protection device reaches end-of-life, and thus alerting me to the fact.

In conclusion, I do think the complaint is somewhat of a storm in a teacup, probably having more to do with competitive and commercial interests than anything else.

We invite responses to the letters page and comment on any industry issues. Email

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