How "Two staging" Minimizes Surges

Q. Why utilize "two staging?"

A. Due to the nature of physics, lead wire lengths, impedance’s, etc... a small but still potentially destructive component of the leading edge of a fast high energy transient will pass by the service entrance Meter-Treater^® device. This happens even as the Meter-Treater® MOVs are beginning to clamp on it.  

This fast edge must be dealt with by a high quality second stage device. This should be located at the point of use, plugged into a grounded outlet, and the sensitive equipment "load" then plugged into it.

Q. What is "overvoltage protection coordination," and how is a high energy lab test conducted?

A. About overvoltage protection coordination and lab testing.

History:
The proper coordination of surge protection has long been practiced by the Power Companies. Usually starting with transmission lines through distribution and finally secondary to the transformer. The same concept has long been advocated in both commercial and residential power protection designs. In the residential or light commercial application this would take the form of building entrance protection, preferably starting at the electric meter and then a local application at the equipment to be protected. Past selection of clamping devices has been a matter of failure experience due to lack of investigations into good residential anti-surge coordination.

Drawbacks:
Until recently, surge generators large enough to actually drive substantial surge through a house were quite rare. Small 10,000 amp table top generators used to bench test equipment were incapable of driving a large enough surge through the household wiring. Also, prior to four channel DSO oscilloscopes, the current diversion as well as the clamping voltage result was very hard to capture.

About The Test:
Meter-Treater’s large custom surge generator was used to drive up to 60,000 amps into a “house” wiring configuration starting at the meter can. This is six times the ANSI requirement and provides the home owner with lots of protection headroom. At the meter can, a building entrance surge protector was put into place. Two different brands of outlet protectors were placed into an outlet 50 feet down stream at the end of the romex wire.

The total surge current for the “lightning strike” was measured at the ground return with a Pearson Pulse CT as well as at the outlet with an additional CT. The clamping voltage was measured at the outlet with HV probes. All data collection for each shot was accomplished with a Gould 4 channel Digital Scope.

Q. Will Meter-Treater®’s also protect against TOVs?

A. Even though Meter-Treater^®’s have been documented by some utilities in the past to have helped prevent damage to systems from some utility TOVs (Temporary Over Voltages), the units are not specifically designed for that purpose. Rather, they are designed for electrical transients, such as are associated with lightning, electrical grid switching, motors starting and stopping, furnace igniters, etc. Faced with a TOV, Meter-Treater^®’s will act just as if a large transient is occurring and clamp on it (diverting it to ground), but at a certain point the coordinated safety fusing will take effect, and the Meter-Treater^® will take itself out of the loop.

(An independent testing laboratory has subjected the device to over-voltages similar to those generated if a neutral connection is broken or corroded. A series of tests were performed applying step increases in ac voltage. The units could withstand up to 200V indefinitely without going into a thermal runaway condition. At 210V, the device went into a runaway condition and disconnected the load within one second. Another measurement of disconnect speed was of the device extinguishing a 2,800 A rms fault in one cycle, due to the benefit of the device’s arc quenching design, in coordination with its custom internal fusing).

Let Through Voltage Results Table

The voltage rise at the outlet is all that is left of the initial surge coming in.