MOV’S

Metal Oxide Varistors (MOV’s), the principal component(s) which divert incoming surge energy into EG conductors in virtually all Shunt Mode surge suppressors, exhibit a “fixed clamping voltage” characteristic, above which they rapidly change from virtual open circuits into low resistance conductors. For a transient surge duration of not more than a few milliseconds, the resulting power dissipation in MOV’s can be tolerated. In the event of a continuous overvoltage condition of any significant duration however, MOV’s rapidly heat up and then either permanently revert to their non-conductive state, or fail catastrophically with the attendant possibility of fire.

Irrespective of cost or manufacturer, the cumulative (sacrificial) effect of repeated surges over time will ultimately cause MOV’s to fail one way or the other. Recent MOV-based surge suppressor devices made to Underwriters Laboratories (UL) 1449–2 (2nd ed.) specifications incorporate a fuse element which disconnects the power in the event of catastrophic MOV failure. Older MOV-based devices do not have this feature, however, and non-catastrophic MOV failure leaves the attached equipment completely unprotected, usually without the knowledge of the owner! To ensure continuously safe operation, MOV-based surge protection devices should be tested on a regular basis.

SHUNT MODE SURGE SUPPRESSORS IN EQUIPMENT NETWORKS

It is not uncommon to encounter “Shunt Mode surge protected” equipment interconnected by network cables to other equipment elsewhere in a building which, for whatever reason are NOT connected to Shunt Mode surge suppressors. During a surge event, “unprotected” equipment will experience little if any elevation of its ground reference potential, whilst “protected” equipment will experience an abrupt and often substantial rise in its ground reference potential. The resulting surge currents flowing in network cable ground loops are thus considerably increased by the use of Shunt Mode surge suppressors at only one or some equipment locations•rather than ALL locations involved in the network. Installing identical Shunt Mode suppressors at all equipment locations may reduce the magnitude of this problem, but only to the extent that the impedances of each ground path into which noise energy is shunted are the same, a condition which is not likely to exist in all but the smallest of systems.

THE SERIES MODE ALTERNATIVE

SurgeX Series Mode surge suppressors act first as low pass filters which simply block the high-frequency (HF) components of powerline surges. The remaining low-frequency (LF) surge energy is diverted into a bank of capacitors where it is stored for the duration of the event and then slowly discharged back across the incoming hot and neutral conductors without involving any connection to Equipment Ground.

SurgeX Series Mode surge suppressors can thus be placed anywhere along a power circuit without the ground reference elevation disadvantage of Shunt Mode surge protection devices. SurgeX Series Mode surge suppressors incorporate “floating clamping voltage” circuitry which will withstand considerable overvoltage conditions of indefinite duration without damage or degradation of performance, and are UL certified to a Surge Endurance specification of A-1-1, the highest possible rating available [2]. Most importantly, SurgeX Series Mode surge suppressors do not incorporate sacrificial components of any kind, effectively guaranteeing an unlimited service life without the requirement for testing and/or periodic maintenance.

THE BOTTOM LINE

During a surge event, Shunt Mode surge suppressors located at the equipment load end of a branch circuit will cause an increase of local ground reference potential regardless of manufacturer and/or price. Without periodic testing there is no guarantee of long-term protection due to the sacrificial nature of key components used in these devices.

SurgeX Series Mode surge suppressors do not require periodic maintenance or testing, and do not cause an elevation of the local Equipment Ground reference potential during surge events regardless of where they are installed in an electrical power system. This is truly a quantum leap in real powerline SURGE PROTECTION!

References:
[1] N. A. Muncy, Noise Susceptibility in Analog and Digital Signal Processing Systems, J. Audio Eng.
Soc., Vol. 43, No. 6, 1995 June
[2] The UL A-1-1 Surge Endurance testing procedure involves the application of a minimum of 1000
surges of 6,000 Volts at 3,000 Amperes (the highest surge voltages and currents likely to be encountered
in a typical building), as specified in IEEE/ANSI C62.41-1991.