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#10327 06/06/02 08:02 AM
Joined: Jul 2001
Posts: 311
Beyond voltage, frequency etc. how are surge arresters sized? The surge arrester will be connected to the service conductors. For this example, would the same size surge arrester be used for a 120/240V, single phase, 100 amp service or for a 120/240V, single phase, 400 amp service?


#10328 06/06/02 07:39 PM
Joined: Oct 2000
Posts: 5,392
just speculation here, but i would venture that arrestors be sized in accordance to problems external...
It should be given some thought, for the sake of $400 +- of AFCI's in a panel here.

#10329 06/06/02 08:23 PM
Joined: Mar 2002
Posts: 582
Ron Offline
Many Things to keep in mind.
Voltage ratings
Type of protection (Catagory A = low, B = Medium, C = high exposure to intense surges)
Breif explanation:
Good examples and info:

Generally the device does not have an ampere rating because they are conencted in parallel to the protected conductors/equipment.

[This message has been edited by Ron (edited 06-06-2002).]

#10330 06/06/02 10:42 PM
Joined: Apr 2002
Posts: 2,527
One aspect that seems to get glossed over is the critical minimization of inductive reactance in conductors between the ‘magic black box’ and bus taps. A three-foot run of #4s severely limits the arrestor’s capability to clamp voltage AT THE 400A BUS. Basic laws of physics are often ignored.

#10331 06/07/02 07:08 AM
Joined: Jul 2001
Posts: 311
Thank you for replies. I'm not up on surge arrester technology. I'll need to study more. Good links. Over the last week or so we've had quite a few storms in Western Pennsysvania.

I had a discussion with my Supervisor concerning the possibility of installing surge arrerstors on line side of service disconnect and T.V.S.S. (Transient Voltage Surge Suppressors) on the load side of the service disconnect in several of our buildings.

#10332 06/07/02 11:47 AM
Joined: Apr 2002
Posts: 2,527
There are arrestor packages "listed for use as service equipment," but I'd be sure that the utility will buy into your plan before you show up at a customer’s site with heavy cardboard box in hand. Taps should ideally be installed downstream of the metering but before the servce disconnect. [That may involve breaking a seal, so keep the utility in the loop. It’s a bit embarrassing to have a customer without a day’s worth of power while a dispute is going on.]

It’s crucial to keep the tap conductors as short as possible. The arrestor guys may promise the world, but understand that those numbers can be made instantly worthless because they are based on tests at the arrestor terminals, and surge ratings will always be lower/slower at the other end of the tap.

This text and links are intended ONLY as an example. GE just seems to explain the problem fairly well. They differentiate the connection as “Tee-” versus “Series-connected.”
GE hawks a true Kelvin-connected series, but they’re limited to a 100-ampere-continuous circuit rating.

The only time these comments would not apply is where a equipment company insisted on some blind installation of a ‘showpiece’ arrester to fulfill some mealymouthed insurance or warrantee clause, with no real concern that it had to work properly. That’s where the little blobs with a locknut and three-foot leads prove useful. (Too many arrestor salesguys proudly list Durro-Test in their resumes.)

Regional variations and local customs will determine how this applies to you.

#10333 06/07/02 01:41 PM
Joined: Jul 2001
Posts: 311
Good advice which I will keep in mind.

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