A question I get quite frequently is: "How much is a distribution arrester worth?"  I always consider this a good question because the answer is not very obvious.  Arresters are silent sentinels of the equipment to which they are attached,  they make no record of saving their subject, they have no outward evidence that they have saved the system from an outage like a fuse or breaker, and they stand ready for decades.  Because of their inconspicuous nature, they are completely taken for granted during their service and their value is assumed to be equal to their cost, which is entirely incorrect.   

To better understand this concept, read     ArresterFacts 038 on Calculating the Value of a Distribution Arrester 

or just run the Calculator and check the Value of Distribution Arresters in your region.

In May of this year, the Eaton Corporation board of directors and the Cooper Industries board of directors agreed that Eaton would acquire Cooper in its entirety.  This acquisition is still under way and is expected to be finalized this quarter when shareholders of both companies approve it as well as the US SEC.  Share holder meetings to vote on the transaction are being held on October 26th by both Eaton and Cooper.  When the acquisition is completed, Eaton will be an off shore company, as was Cooper Industries, with incorporation in Ireland.  The combined company will have about 18B USD in sales with electrical products being about 50% of that. For comparison, Cooper was $6B in sales, Siemens is an $85B company, ABB is a $40B company, Hubbell is $3B and MacLean Power Systems is an $800M dollar company.   The New Eaton is expected to be called Eaton Global Corporation PLC with headquarters likely remaining in Cleveland Ohio and Alexander (Sandy) Cutler will remain the CEO and major driver of the business.   Both Eaton and Cooper have roots that are well over a hundred years old.   

The products and markets of Eaton and Cooper are very complementary to each other and it is expected that synergies will enhance both the new Eaton as well as the markets they serve.  Of course the product of interest to this writer is surge protection.  Both Eaton and Cooper manufacturer and sell low voltage type SPD devices. Eaton has a wider verity of SPDs from the very high end to the breaker panel end.  Eaton has kept the Cutler Hammer brand in production and is sold through retail and industrial channels.  The Cutler Hammer products compete head to head with the Cooper Bussmann products.  The Cooper Bussmann SPD and TVSS devices are almost all breaker panel mounted devices and these are very similar to the Cutler Hammer brand.  Additionally, Eaton also has low voltage whole house protectors similar to Cooper's Stormtrapper HE series.  However in the medium voltage markets, Eaton has no arrester products so the Cooper MV and HV arrester line will be a nice expansion to the "New Eaton" surge protection product lines.

A good product offering is very important, but how the sales forces' combine to sell these products is just as important and cannot be underestimated.  It is going to be very interesting to see how this all settles out.

A question came in recently to ArresterWorks regarding ArresterFacts 033.

The basic question was:

The test procedures indicate that one or more surges of square wave or � sin waves with 2-4 ms in duration can be used to raise the arrester temperature during the Operating Duty Test to its maximum stable limit.  However the formulae offered in the ArresterFacts 033 to calculate the energy requirement from a systems perspective assumes a single switching surge. 

Is it acceptable to compare a multi-surge thermal energy rating to a single surge requirement? 

After considering the question my response was:

Indeed, the thermal energy test can be a one or more surge test and the thermal rating is the sum of the thermal energy of all the surges it took to raise the temperature of the arrester to its point of instability.

Also as you point out, the quick formula for calculating the thermal energy requirement on a system is a single surge analysis.

It is the generally accepted understanding that the number of surges it takes to raise the temperature of an arrester to its thermal limit is not relevant to the test, therefore multiple impulses are allowed.     When running a system analysis either by transient software or the simple formulae in 60099-5 it is the total energy requirement and could be from either one or multiple surges. 

As a result of this question I have revised 

ArresterFACTS 033.  Additionally it reflects the recent modifications to include  sub classes of station and distribution arresters. Improved  protective level definitions were also added.

Read ArresterFacts 033  Understanding the New IEC Energy Tests