No-nonsense Computer Surge Protection: 
Wrong Choices Can Cause Failures 
 
Wendell H. Laidley, President 
Zero Surge Inc. 
Bernardsville, New Jersey 

 
Introduction Modern desktop computers use complex, sophisticated, 
and very delicate, microprocessor circuits hardly dreamed of only a 
decade ago.  The explosive proliferation of extremely fast "plug-in" 
computers with powerful user-friendly software has brought huge 
computing capability to virtually every office in America today, and 
to many homes. 
 
The combination of faster computers at lower prices has spawned huge 
growth in sophisticated and critical applications, with users 
becoming increasingly, some say even dangerously, dependent on their 
computers. 
 
Despite its incredibly low cost, today's plug-in computer is a 
highly sophisticated instrument, and its faster speeds and more 
densely packed circuits have made it more vulnerable than its 
predecessors to powerline surges.  In response, computer owners have 
accepted the notion that they need surge protectors, whether or not 
they understand how such protectors work.  As LAN Magazine says 
(December 1990), "Surge protectors are widely used, but poorly 
understood".  The lack of understanding by most consumers combined 
with the absence of objective and relevant comparison criteria, have 
inspired an active, energetic industry of surge suppressor 
manufacturers, with products of widely varying effectiveness. 
 
What Are Surges? 

Surges are packets of unusable energy, like shock waves, propagating 
through the powerline.  Their high voltage potential, up to 6000 
volts in 110 volt power systems, makes them dangerous to delicate 
electronic components in their way as they search for paths to 
ground.  Although they contain little total energy, their intensity 
can seriously damage and disrupt electronics, while being generally 
harmless to ordinary electric power equipment like heaters, motors 
and refrigerators.  Surges are picked up by the powerline from 
magnetic fields such as lightning, and from events on the powerline
such as power factor correction, load shedding, and faults.  They 
propagate like shock waves or tidal waves, not harming the powerline 
itself, but posing serious dangers to electronic loads in which they 
expend their energy as they flow to ground. 
 
How Do Surge Protectors Work? 

Ordinary surge protectors simply divert surges from the hot line 
(the only source of external surges, since the neutral and ground 
circuits are grounded at every service entrance) to the neutral and 
ground wires, where they are assumed to flow harmlessly to earth, 
the ultimate surge sink.  These surge suppressors use metal oxide 
varistors (MOVs) and/or other similar shunt components which sense 
the high voltage of a surge, and quickly change state from an open 
(non-conducting) circuit, to a very low impedance short circuit for 
the duration of the surge.  When the surge voltage disappears, the
MOV returns to an open circuit, much like a pressure relief valve 
closes.  In this way, the protector diverts mainly the surge energy 
and not significant amounts of powerline energy, because of the 
short duration of the surge, unless the MOV has degraded in its 
normal wearout process to the point where it "clamps" on the 
powerline.  When that happens, the MOV explodes and fails, leaving 
the surge protector unable to provide any protection. 
 
An explanation of this performance vs. service life trade-off with 
MOVs, and an appeal to the industry to minimize the risk of 
premature failures, was presented by Martzloff and Leedy in their 
paper "Selecting Varistor Clamping Voltage: Lower Is Not Better!"  
In it, the authors urge protector makers to avoid the race to 
provide "better" protection, at the expense of protector service 
life, since MOVs degrade in service and have caught fire.  Vernon L. 
Chi, Director of the Microelectronic Systems Laboratory at the 
University of North Carolina at Chapel Hill says "The singular 
virtue of the shunt type protection device is that it's 
inexpensive."  The process of diverting unwanted surge energy to 
ground in a conventional surge protector is shown schematically in 
Figure 1. 
 
Cost of Computer Failure 

As users become more dependent upon their computers, the cost of 
failure often means lost productivity, lost data, and disaster 
recovery, and generally far exceeds the simple cost of hardware 
repair.  The New York Times reported in September 1989 that the 
average Fortune 1000 company incurred losses of $3.48 million from 
Local Area Network failures, which occurred an average of 23.6 times 
per year, for an average of 4.9 hours duration.  Of this total 
costof computer failure, hardware repair was only a minor component. 
Those who doubt the cost and disruption caused by computer failure 
need only ask someone who has experienced one. 
 
Networks and Modems Bring New Problems 

Computers interconnected by datalines present a whole new problem 
because network (and modem) datalines use the powerline ground 
circuit for signal voltage reference.  When a conventional surge 
protector diverts a surge to ground, the surge directly enters the 
datalines through the ground reference. As Martzloff explained in 
"Protecting computer systems against power transients"(IEEE 
SPECTRUM, April 1990), this causes high surge voltages to appear 
across datalines between computers, and dangerous surge currents to 
flow in these datalines.  Data Communications reported in December 
1990 that "Most experts now agree that TVSSs [Transient Voltage 
Surge Suppressors] based on conventional diversion designs should 
not be used for networked equipment." LAN TIMES commented in May 
1990 "Surge protectors may contribute to LAN crashes by diverting 
surge pulses to ground thereby contaminating the 
reference used by data cabling."  
 
This problem was first discovered by a team of National Institute of 
Standards and Technology (NIST) researchers led by Martzloff in 
1988.  After they had performed some surge experiments on the 
powerlines in an industrial building, office workers reported damage 
to the data ports of their printers.  On reflection, Martzloff 
concluded that the computer's shunt suppression circuitry had 
diverted the powerline surge to ground and created a surge current 
in the printer dataline, which damaged the printer data ports.  
 
What Protection Do Computers Need? 

Because of secondary problems created by surges after they have been 
diverted, conventional unfiltered shunt surge suppression is 
unsatisfactory for plug-in computers.  The laws of conservation of 
energy must prevail, and until this energy reaches earth, it poses a 
danger to electronic loads in its path.  Adequate point-of-use 
protection for increasingly complex computer configurations requires 
that the surge energy be captured and released safely at a 
controlled rate, rather than simply be diverted to wreak its havoc 
elsewhere.  A reliable surge suppressor would provide the following 
protection: 

         - keep let-through voltage under 250 volts 
         - preserve the integrity of the ground circuit as a clean 
             reference  for datalines 
         - provide noise filtering and attenuate the fast rise times 
             of all surges, to prevent stray surge coupling into 
             computer circuitry 
         - intercept all surge frequencies, including high frequency 
             surges generated inside buildings, due to current 
             interruption on branch circuits 
         - not use components that degrade in service. 
 
The Ideal Surge Protector 

The ideal computer surge protector would interrupt the power for the 
short duration, e.g. 50 microseconds, of the surge, then reconnect 
the circuit, as shown in Figure 2.  Unfortunately, no switch exists 
today that can respond this fast, so this effect must be simulated 
by a circuit. 
 
A Practical Solution 

A circuit solution which provides a high impedance to the surge 
while presenting a low impedance to the power wave is embodied in 
the patented new Surge Eliminator from Zero Surge.  This unique 
protector employs a floating surge clamp which rides on the peak of 
the AC powerline wave and immediately captures any surge which 
exceeds the AC power wave envelope.  Noise filtering within the 
dynamic range of the AC power wave (+ 180 volts) slows the surge 
slew rate enough to enable the floating clamp to intercept the surge 
within 20 volts of the powerline peak, and successive stages of 
energy storage capacitance are brought into the circuit by sensing 
circuits measuring slew rate and surge amplitude.  The stored energy 
is then released slowly to the neutral circuit, without disturbing 
the critical reference ground.  The action of this dynamic clamp is 
shown in Figure 3 and the resultant surge energy paths in Figure 4. 
 
This comprehensive energy storage circuit, which uses no wear parts, 
meets all the requirements for effective, non-degrading protection 
for modern plug-in computers.  The circuit acts like a tennis net or 
a bucket with a hole in it, capturing the sudden rush of surge 
energy then slowly releasing it harmlessly to the neutral conductor. 
The circuit clears itself quickly enough to suppress repeated 6000 
volt surges of unlimited current at the known 30-50 millisecond 
interval between multiple lightning strikes and so cannot be 
overloaded by the most severe natural phenomena. 
 
Conclusion 

Dependable surge protection is an important factor in computer 
reliability.  Buyers of commercial surge protectors need to be 
informed of the technology employed in the various surge protectors 
they are considering.  Particularly they need to know if the 
proposed surge protection technology is compatible and not in 
conflict with their application, as most surge suppressors are in 
conflict with modems and networks.  The growing use of plug-in 
computers in critical applications, and the importance of effective, 
reliable surge protection to keep them operating, demands that 
consumers be honestly informed of the real characteristics of their 
surge protector, through industry standard performance tests like 
those for other products. 

Underwriters Laboratories deserves credit for the first objective 
performance test in their 1449 standard, but UL should not be 
responsible to establish and maintain useful performance standards 
in the fast-changing and controversial world of plug-in computers.  
Hopefully this NIST Forum will lead to some appropriate consumer 
guidelines, but until reliable standards and specifications are in 
place, consumers will be left to "buyer beware" in the jungle of 
computer power protection suppliers promoting various devices 
of varying effectiveness. 

 
References 

1.  "Super Powers - How to Protect your LAN from Electricity's 
      Ills", LAN Magazine, December 1990, p.75. 

2.  Andy Baird, "Surge 'protectors' - worse than useless?", 
      Princeton Macintosh Users' Group Newsletter, June 1990. 

3.  "Surge Suppression for Networks: Problems, Myths, & Solutions", 
      ISPNews, March/April 1991, p.36. Figure 1 (exploded MOV). 

4.  Francois D. Martzloff and T.F. Leedy, "Selecting Varistor 
      Clamping Voltage:Lower Is Not Better!"  Proceedings of the 
      Zurich International EMC Symposium,April 1989. 

5.  "SAFE-ALERT" Report of Fire Incident with MOV Surge Protector, 
      Government-Industry Data Exchange Program, September 20, 1988. 

6.  Vernon L. Chi, "Zero Surge Model ZS1800 Surge Eliminator - 
      Product Review and Report,"Department of Computer Science, 
      University of North Carolina, Chapel Hill, July 31, 1990. 

7.  "Beware Those Network Failures", The New York Times, Peter H. 
      Lewis, September 17, 1989, p.F 11.                

8.  Francois D. Martzloff, "Protecting Computer Systems Against 
      Power Transients", IEEE SPECTRUM, April 1990, p. 37. 

9.  "Reconsidering Power Protection", Data Communications,December 
      1990, p.72. 10. "Surge Protection Revisited", LAN Times, May 
      1990, p.89. 

11. Francois D. Martzloff, "Coupling, Propagation, and Side Effects 
      of Surges in an Industrial Building Wiring System" Conference 
      Record of the IEEE-IAS 1988 Annual Meeting,  pp.1467-75.
 

