Surge Testing: 

Don’t Kid Yourself, Don’t Kill Yourself

François Martzloff

National Institute of Standards and Technology

Gaithersburg MD 20899

Reprinted from EMC Technology, July/August 1988 

Significance:

Part 5 – Monitoring instruments, laboratory measurements, and test methods

Progress report to the EMC community on the development of what became IEEE Std C62.45 from the

point of view of a trade magazine. 

Explains the need for careful planning of a test program, differences between testing for immunity versus

vulnerability, the need to consider powered testing, and appropriate methods for coupling the surge into

the test circuit. Lists other practical aspects of surge testing, last but not least the mandatory safety

review of the tests procedures.
Surge Testing: Don't Kid 

Yourself, Don't Kill Yourself 

by Fran~ois D. Martzloff 

National Bureau of Standards 

Gaithersburg, MD 20899 

ncreasing awareness of the sensitivity of electronics to surge 

effects has led to a proliferation of surge suppressors on 

the market. Confronted with a difficult choice, some users 

are evaluating the performance of these devices by surge testing. 

However, the techniques involved in these tests are different from 

typical EMC testing because of the single-shot nature of the event 

and because of the potential personnel hazards involved in surge 

testing. This article presents a brief overview of surge testing, focusing on the unique techniques involved in performing valid tests 

under safe conditions. 

In the old days of electromechanical devices, surge testing was 

an alternative to hi-pot testing, aimed at demonstrating the dielectric strength of equipment. Today, the emphasis is on 

demonstrating the immunity of electronic systems against upset 

or damage by surges occurring on power or data line interfaces, 

or evaluating the effectiveness of surge suppressors. The traditional 

tests were performed in high-voltage laboratories by specialists, 

but the new tests can be performed by anyone with a benchtop 

commercial surge generator and suitable oscilloscope. This welcome 

simplification, however, is not without dangers: the danger of 

overlooking technical subtleties (don't kid yourself) and real 

hazards (don't kill yourself). 

The Surge Protective Devices Committee of the IEEE has completed a new document, "Guide on Surge Testing for Equipment 

Connected to Low-Voltage AC Power Circuits," ANWIEEE 

C62.45-1987, which addresses many of these concerns.* The major concepts can only be summarized here; practitioners and planners of surge testing are urged to consult the IEEE guide. These 

major concepts (10 commandments?) are the following: 

1. Plan ahead! 

2. Differentiate between testing for susceptibility and testing for 

vulnerability. 

3. Consider the need for applying the surge superimposed on the 

ac power. 

4. Provide for realistic combined, not separate, voltage and current tests. 

5. Provide adequate coupling of the surge into the test power line. 

6. Isolate the room power supply from the surge with a 

back-filter. 

7. Consider the polarity and phase relationship of surge timing. 

8. Consider the implications of repetitive application of single 

surges. 

*The figures are reprinted from ANSVIEEE C62.45-1987, Copyright 1987 

by the Institute of Electrical and Electronics Engineers, Inc., by permission of the IEEE Standards Department. The concepts outlined in this article 

reflect that document. The contributions of the IEEE working group 

members to the development of the "Guide," and thus this article, are 

gratefully acknowledged. 

9. Monitor the surge with suitable instrumentation. 

10. Last in the list, but first when operating, be safe. 

1. Plan Ahead. 

There is more to surge testing than connecting the test article 

to the output terminals of a zapper and watching for smoke. Every 

aspect of testing must be considered and coordinated. Figure 1 provides a graphic illustration of the interactions between goals, outcomes, equipment and procedures. 

2. Differentiate between testing for vulnerability and testing for 

susceptibility. 

Surge protective devices are often applied only for avoiding 

damage; however, they can also serve to prevent upset in the operation of the equipment. Therefore, the subject of surge testing must 

recognize both outcomes of a surge: upset (susceptibility) and 

damage (vulnerability). This differentiation must be defined before 

PURPOSE - Pare Fall - Whd Happened" 

+ outcomes 

POWERED 

rr UNPOWERED Powad w 

Unmwereo Pavered 

PROCEDURES 

TYPICAL 

RELEVANT 

REFERENCES 

TEST 

SCHEDULE 

Fig 1 

Guiding Considerations for Surge Testins 

Figure 1-Considerations Involved in Planning a Surge Test 

JULY-AUGUST 1988 35 
the tests are conducted so that the parties 

involved can agree on appropriate pasdfail 

criteria. 

3. Consider the need for applying the 

surge superimposed to the ac power. 

Test surges can be applied to the equipment under test (EUT) in two ways: (1) 

with normal operating power disconnected 

from the EUT (unpowered testing), and (2) 

with normal operating power applied to the 

EUT (powered testing). The intended purpose of the test determines whether one approach is sufficient or whether both are 

required. 

Un~owered testing mav aoDear sufficient 

in situations for which the test outcome 

does not depend on evaluation of EUT 

performance during the surge. For instance, clearance flashover of an electromechanical device might be the failure 

criterion; in that case, there usually should 

be no need to power the EUT. However, 

unpowered testing does not represent actual service conditions. 

Powered testing is necessary under two 

circumstances: (1) when the test outcome 

depends on evaluation of EUT functional 

performance during the surge, and (2) when 

determination of EUT vulnerability can involve power-follow (which may also devend in Dart on the vhase anele at which 

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the surge is applied with respect to the line 

voltage wave). Thus, a test for susceptibility 

implies normal equipment functioning 

prior to the surge; therefore, it can only be 

checked in the powered mode. From the 

standpoint of good practice, it is best to 

perform laboratory tests in a manner that 

most closely simulates the actual service 

environment. 

4. Provide for realistic combined, not 

separate, voltage and current tests. 

The nature of the EUT will affect its 

response to an applied test surge. A highimpedance EUT, such as a winding, a 

clearance or a semiconductor in the blocking mode, will be stressed by a voltage 

surge. In these cases, the energy associated 

with the surge is not significant. A lowimpedance EUT, such as a circuit containing filter capacitors or surge-diverting protective devices, will be stressed by a current 

surge; the energy deposited in the components becomes a significant factor in this 

type of surge occurrence. 

Therefore, the wave shapes for both 

voltage and current tests therefore must be 

considered in specifying a test procedure. 

Thus, the generator should be capable of 

a dual role: (1) For an expected voltage test, 

a sudden impedance drop must be accompanied by a specified surge current 

(amplitude and wave form) to ensure both 

marking the defect and initiating powerfollow current. (2) For an expected current 

test, the voltages involved must be held between a low and a high limit to initiate current by a sparkover-type device while not 

exceeding an appropriate upper limit. 

While the need for providing these two conditions may not always be apparent, ignoring them can lead to meaningless testing. 

An example is if a generator of high internal impedance or low stored energy is applied for performing a voltage test on an 

EUT which has relatively low input 

impedance. 

5. Provide adequate coupling of the surge 

into the EUT power supply. 

Coupling the surge to an unpowered 

EUT is a simple matter: just connect the 

EUT to the terminals of the surge 

gcrlclarul. IU LIIC ~rlb~ UL a ~UWCICU LCSL, 

however, the coupling becomes a complex 

matter. This complexity is the result of the 

need to apply the surge to the Line supplying the EUT, maintaining the specified 

waveform while transferring the necessary 

energy to the EUT. Simple two-terminal 

devices can be subjected to the surge in a 

simple configuration; multi-terminal 

devices require careful attention to specifying which terminals are surged with 

36 EMC TECHNOLOGY 
respect to which others. This concern is 

often described as testing for common 

mode or testing for normal mode. Because 

a detailed discussion would take a whole 

article by itself, this concern is only mentioned here. 

6. Isolate the room power supply from 

the surge with a back-filter. 

A further complication introduced by 

powered testing is the need to isolate the 

room power supply from the test circuit 

with a back-filter. There are two good 

reasons to do this: (1) The purpose of the 

test is to subject the EUT, not the whole 

laboratory, to the test surge. (2) The 

relatively low impedance of the room 

power supply would load down the surge 

generator and prevent it from delivering the 

desired amplitude for the test surge. The 

design of this back-filter, however, is not 

trivial because the filter must allow enough 

line current to supply the normal load current to the EUT but cause a minimum of 

interaction with the pulse-shaping network 

of the surge generator. 

7. Consider the polarity and phase relationship of surge timing. 

Depending on the nature of the EUT, the 

polarity of the test surge may have an effect on the EUT response. A more subtle 

effect may involve the timing of the test 

surge with respect to the power-frequency 

sine wave: the effect of a surge on a power 

semiconductor may be different if the 

device is in reverse bias or is conducting at 

the time the surge is applied. If the behavior 

of the EUT involves a sparkoverintentional or accidental-the timing of the 

surge affects the power-frequency current 

initiated by the sparkover. 

8. Consider the implications of repetitive 

application of single surges. 

The test surges are single events, but they 

will be applied many times to the EUT for 

a number of reasons: (1) Prudent practice 

is to start a test with a low-severity test and 

increase the severity level in steps to determine the threshold of interference or 

damage. One important aspect of this procedure is the risk of overlooking blind spots 

in the performance of the EUT if the test 

surge were applied only at the maximum 

severity level. (2) The need for bipolar 

testing and exploring the effects of phase 

relationship of the surge timing quickly 

multiplies the number of shots required to 

cover all the possible conditions. (3) Worse 

yet, should the EUT response involve timing of the surge with the internal clock and 

transitions of the EUT logic, then we may 

be considering thousands of single pulse applications! Thus, the cumulative effects of 

all these surges on the EUT (such as 

temperature rise at fast repetition rate, 

long-term degradation even at slow repetition rate) must be considered. Some 

average power limitation must be defined, 

as well as a waiting time between surge 

applications. 

9. Monitor the surge with suitable 

instrumentation. 

The need to monitor the input surge is 

axiomatic for verifying the characteristics 

of the applied surge, both open-circuit and 

as modified by the load. For simple failure 

modes of isolated components, such as insulation breakdown or permanent semiconductor damage, monitoring the applied 

surge reveals a failure as the applied voltage 

wave is chopped. Checking a complex EUT 

for susceptibility requires more extensive 

instrumentation to detect a misoperation. 

(That instrumentation itself must be immune to the disturbances created in the area 

by the test surge.) 

Monitoring within the EUT may also be 

required to understand the failure 

mechanism under the surge, or to control 

one or more critical voltages within the 

EUT. It may also be required to check the 

amount of surge remnant or surge letcontinued on page 38 

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Circle No. 201 on Reader Retrieval Service 
Surge Testing 

continued from page 37 

through reaching specific critical components. 

10. Be safe! 

There are two major considerations in the quest for safety during the test procedure. The first, fairly obvious, is that the voltage 

and energy levels applied to the EUT are generally hazardous and, 

therefore, deserve respect. That respect is best enforced by providing a barrier around the test circuit, including all of the EUT 

and leads that are not disconnected during the test (see Fig. 2). 

The second, less obvious consideration is that under fault conditions (which are not always predictable) high voltages can appear 

at unexpected points during a flashover or between points considered to be "ground potential." In surge testing, there is seldom 

anything that can be considered "ground" within the EUT. All 

of the monitoring measurements must be accomplished by differential connection of the probes (see Fig. 3). This type of connection 

enables use of a safely grounded oscilloscope with high-voltage 

probes that have no ground leads attached to the EUT, while the 

chassis of the oscilloscope is safely grounded by the grounding conductor of its ac power cord. Note that the grounding pigtails of 

the probes are not connected to the "ground" of the EUT. The 

practice of a floating scope should be studiously avoided in surge 

testing. This requirement, however, introduces concern about the 

common-mode rejection ratio of the instrumentation, a source of 

errors if not properly addressed. This last concern provides a good 

example of the duality of surge testing implied in the title of this 

article: safety must not be compromised, even if mandatory safety procedures could lead to more difficult measurements. Using 

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EMC TECHNOLOGY 

an unsafe test method in the belief that it is the only one yielding - 

valid results is not acceptable. The perceptive, prudent and proficient operator will keep both imperatives in mind and emerge alive 

from the tests, with reliable results. 111 

I1 I I I I 

. Surge AC Interface 

Surge Other Pemts. . Surge Component Termlnam 

Unknown EUT lmpedanoc 

Hlgh EUT Impedance LOW EUT Impedance 

. EUT with Impsdance mat 

Chanoer Durlnp the Test 

v 

Tw ol Svge Gsnetntw 

I I I I I Monltonng Ihs EUT I [ Surge Coupler I 

Figure 2-EUT Being Surge Tested, Showing Required Interfaces, Filters, and Reterminations 

Figure 3-Monitoring within Surged Equipnlent with Voltage 

Probes in Differential Connection 

Note: contributions by the NBS are not subject to U.S. copyright; this article may be reproduced without restriction. 

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