IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 1, JANUARY 2004 151

Lingering Lead Length Legacies in Surge-Protective

Devices Applications

François D. Martzloff, Life Fellow, IEEE, and Kermit Phipps, Member, IEEE

Abstract—Two experiments are reported to show how some lingering inherited misconceptions about the applications of surgeprotective devices (SPDs) can lead to erroneous or cost-ineffective

attempts to address the issue of lead length. The first experiment

demonstrates the fallacy of the “four-terminal SPD” configuration

if taken at face value without additional precautions on lead dress.

The second experiment provides quantitative information on the

actual effect of lead length. With this information, designers and

installers can place the issue in a realistic perspective and avoid

unnecessary effort.

Index Terms—Electromagnetic coupling, length measurement,

surge protection, testing, voltage measurements.

I. INTRODUCTION

MANY references found (inherited) in the literature imply

that lead length is a significant factor to consider for

correct installation and characterization of surge-protective devices (SPDs). This perception has led to the design of “fourterminal” one-port SPDs where the incoming power must be

routed through the device terminals,1 rather than using an SPD

with simple shunt connection with a pair of leads of unspecified

length connected at some point of the system. However, both

perception and design miss the point that the problem is actually

one of mutual inductance as well as “lead length.” It is indeed

important to recognize that to achieve an optimum surge protection, connecting leads of SPDs should be as short as possible.

Yet not only long lead lengths, but also significant loop area

formed by the connecting leads, will add an inductive voltage to

the protective voltage of the SPDs, degrading their performance.

The perception was further complicated by concerns about the

“speed of response” issue. After a brief review of some old issues, this paper reports the results of two experiments aimed at

placing the lead length issue in the proper perspective.

II. HISTORICAL PERSPECTIVE

Concerns about the undesirable performance degradation

of improperly installed surge-protective devices are not new.

In the high-voltage arena, the concepts of “separation effects”

and “connecting lead wires” have been recognized for more

than a half-century (Witzke and Bliss, 1950 [1]); (IEEE Std.

Manuscript received August 19, 2002. Contributions from the National Institute of Standards and Technology are not subject to U.S. copyright.

F. Martzloff is with the National Institute of Standards and Technology,

Gaithersburg, MD 20899-8113 USA (e-mail: f.martzloff@ieee.org).

K. Phipps is with EPRI PEAC Corp., Knoxville, TN 37932 USA.

Digital Object Identifier 10.1109/TPWRD.2003.820212

1This “four-terminal SPD” is a one-port, shunt SPD, which should not be

confused with the two-port SPD. See definitions and notes in IEC 61 643-12

[3].

Fig. 1. Response of MOV to nanosecond pulse [4].

C62.2-19872 [2]), and the recent IEC 61 643-12 (2002) [3]

is a comprehensive guide for low-voltage applications.3 In

the low-voltage arena, the situation has been complicated by

misguided attention to the issue of “speed of response” and

concerns about “overshoot” in the application of SPDs, fueled

by debates about relative merits of emerging technologies such

as metal-oxide varistors (MOVs) and silicon avalanche diodes

(SADs). The debates on this issue were quite active soon after

introduction of MOVs and SADs in the seventies. At that time,

so many papers were published that any attempt to recite them

entails a severe risk of offending the authors who might be

overlooked in a list of references, so that we will not take that

risk here. The debates have now abated although lingering

perceptions or misperceptions remain.

For MOVs, a typical application manual published in the

seventies [4] addressed both the issues of “speed of response”

and “lead length” as illustrated by Figs. 1 and 2 (overleaf)

excerpted from this manual. Other documents, such as IEEE

Std. C62.33-1982 [5] attempted to place speed of response

and overshoot in perspective and de-emphasize the issues, but

were not entirely successful, to wit the claims for nanosecond

response that still appear on the wrapping of some commercial

SPD packages. Some justification for the emphasis on speed

of response can be found in historical context, when interest

was arising about ensuring protection against the nuclear electromagnetic pulse, and might still be valid for some military

applications. In more mundane modern surge protection for

today’s industrial, commercial, and residential ac power circuits, the perspective is different. Reality checks and economic

considerations suggest that these concerns might be an overkill

2In this historical perspective, unlike standards where the latest edition is explicitly specified, we quote the date of the original publication as available to

us. In the case of C62.2, we speculate that the issue of separation effects might

have appeared in earlier standards such as ANSI (not IEEE) C62.2-1981.

3However, this standard needs 123 pages of English text; we are attempting

in this paper to ferret out only the items relevant to this lead length issue.

0885-8977/04$20.00 © 2004 IEEE
152 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 1, JANUARY 2004

Fig. 2. 1978-vintage demonstration of lead length effect with fast-rising surges for two different “lead lengths” (a) Minimal loop area. (b) Excessive loop area.

(c) Current rise of 8 s. (d) Current rise of 0.5 s.

in surge protection for circuits where the propagation of fast

surges is limited [6] and typical wiring practices do not allow

the sophistication of perfect connections in those applications.

Therefore, in this paper we will not go beyond a brief review

of the old issues of speed of response and overshoot, but will

concentrate on discussing the lead length that seems to be the

lingering and misunderstood issue.

A. Speed of Response

For instance, Fig. 1 shows an oscillogram recorded to document the response to fast-rising pulses by an MOV disc inserted in the coaxial test fixture necessary to observe this submicrosecond pulse without test connection artifacts [7]. Indeed,

the experiment confirmed the claim of fast speed of response of

the intrinsic MOV material, but practical devices are generally

not fitted in coaxial packages—just what the tutorial experiment

reported later in this paper did require.

B. Overshoot

In Fig. 1, one might consider that the “TRACE 2” indeed

display an overshoot that may be significant when concerned

with nanosecond response of an MOV. However, for this context

of surge mitigation in ac power circuits, very short picosecond

pulses such as that shown in Fig. 1, or the EFT pulses defined

in IEC 61 000-4-4 [8] and IEEE C62.41-1991 [9] have to travel

only a few meters away from their origin to have their rise time

and duration stretched into tens of nanoseconds or more [10].

Fig. 2 shows the test fixture arrangements and resulting performance for two current impulses with rise times, respectively,

8 and 0.5 [11]. These two rise times were not arbitrarily

selected—our readers will readily recognize what became the

IEEE Std. 587-1980 waveforms [12]. However, creating and injecting the 2.5-kA, 0.5- pulse into the test circuit required

great care, to avoid spurious signals, illustrating again that such

conditions rarely, if ever, do occur in real-world situations [13].

The original figure caption of the GE Transient Manual included

in Fig. 2 mentions both lead length and overshoot, a regrettable

mention—with hindsight—because it focuses attention on lead

length, which is not the direct cause of that “overshoot.”

The perceptive reader at that time might have noticed that the

test fixture sketches in the figure correctly emphasized the issue

of loop area, but the caption provided in the original 1978 figure

is perhaps responsible for launching lead length legacies by focusing on lead length. Small wonder then, that so many lengthy

debates and test specifications have been concerned with lead

length rather than the direct effect of electromagnetic coupling

between the two loops involved in an installation—the injected

surge current loop and the protected equipment loop. Nevertheless, there is some redeeming tutorial value in that figure, which

we will now briefly discuss.

C. Electromagnetic Coupling Between Loops

In Fig. 2, it should be noted that the traces were superimposed

by multiple exposures and are not synchronous, so no attempt

should be made to correlate exactly the timing of the voltage and

current traces. Nevertheless, the inductive coupling mechanism

is apparent in that the maximum voltage occurs at the beginning of the current pulse (maximum ). Observe the large

“overshoot” on the right-side oscillogram for the 22- area

loop and the more modest voltage for the 0.5- area loop. As

further evidence, the amount of “overshoot” for the two traces

disappears at the point of current peak ; at that point,

the voltage trace indicates the “true” level of the voltage limiting

action of the MOV disc, free from spurious inductive effects.

In principle, the coupling aspect is simple, as illustrated in

Fig. 3, which shows how the changing magnetic flux created by

the flow of surge current in the circuit at left (Loop “A”) induces

a voltage in the circuit at right (Loop “B”). Thus, the load that
MARTZLOFF AND PHIPPS: LINGERING LEAD LENGTH LEGACIES IN SURGE-PROTECTIVE DEVICES APPLICATIONS 153

Fig. 3. Coupling of magnetic flux into the load loop.

was expected to be protected at the limiting level of the SPD

actually sees that limiting voltage augmented by the induced

voltage, as shown by the waveforms drawn in Fig. 3.

IEC 61 643-12 [3] also addresses this effect in Annex K.

Figure K-6 of that annex, redrawn here as Fig. 4, is similar

to our Fig. 3, but is relegated to a distant annex. In contrast,

the Fig. 10 of the IEC document (redrawn here as Fig. 5), is

found in the main body under the heading of “Influence of

the connecting lead length” (italics ours) and, thus, appears

to support the four-terminal approach by designating it as

“preferred scheme”—but does not qualify it with a discussion

of the possible electromagnetic coupling.

Note also that this connection arrangement still falls under

the category of “one-port SPD” because there is no impedance

between the “input” and “output” terminals, as would be the

case for a “two-port SPD.”4 So, the idea of “lead length” as a

prime and perhaps sole factor lingers on into the 21st century.

This situation is what motivated us to conduct the experiments

reported in this paper.

To quantify the effect of electromagnetic coupling between

the two loops, we conducted a first experiment using a specially-constructed coaxial SPD to be inserted in a well-defined

configuration of the two loops—the incoming surge loop “A”

and load loop “B” as defined in the schematic circuit representation of Fig. 3.

4The IEC definitions read:

one-port SPD: SPD connected in shunt with the circuit to be protected. A

one-port device may have separate input and output terminals without a specified series impedance between these terminals.

two-port SPD: SPD with two sets of terminals, input and output. A specific

series impedance is inserted between these terminals.

"Note: The current I flows through the SPD, and the magnetic flux due to

this current enters the loop formed by the leads to the equipment terminals. This has the effect of adding an induced voltage to the SPD's

residual voltage. This combined voltage appears across the equipment

terminals."

SPD

Equipment I

Fig. 4. Redrawn figure K.6 and note from IEC 61 643-12.

Fig. 5. Redrawn Fig. 10 “preferred scheme” from IEC 61 643-12.

III. NEW EXPERIMENTS

The first experiment addresses the issue of the inductive coupling between adjacent loops, and the misleading perception

that a four-terminal arrangement, such as that shown in Fig. 5,

automatically circumvents the lead length issue.

The second experiment deals with the real issue of lead length

for shunt-connected (“one port”) SPDs, and provides some quantitative information on the magnitude of the effect as determined

by surge current parameters and, indeed, lead length.

A. Coupling Between Adjacent Loops

For this demonstration, a “coaxial MOV” unit was constructed

as shown on Fig. 6, allowing measurement of the “true” limiting

voltage of the MOV without any significant inductive coupling.

A 40-mm-diameter MOV disc was drilled at its center to allow

connecting the core conductor of a coaxial cable to the top electrode, with the shield of the cable connected to the bottom electrode. Fig. 6 is a cross-section view of the device, which has complete rotational symmetry. A cap (cross hatch) is soldered to the

top electrode and a sleeve (cross hatch) is soldered to the bottom

electrode. Connections could be made at any point of the cap and

of the sleeve; for the purpose of showing the device in a cross-section, terminal connections are represented on the left and on the

right, but are at the same potential. According to the principle of

the “four-terminal SPD,” the incoming power supply (presumed

to include a surge) would be connected at the left of the device,

and surge-free (or at least mitigated) power for the protected load

would be available at the right of the device. The “true” MOV

voltage resulting from a surge can then be observed at the end of

the coaxial cable.This structure wasonly aimedat thedemonstration, not as a practical low-voltage SPD, but was inspired by old

discussions on how to make a distribution arrester consisting of

three parallel-connected stacks of MOV discs arranged at 120

with the power take-off at the center of the triangle [14].

Using this special coaxial MOV, measurements were performed on several simplified configurations of lead geometry,

including the so-called “four-terminal SPD” suggested by
154 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 1, JANUARY 2004

Fig. 6. Coaxial arrangement of test MOV.

To DSA (2)

Surge

Generator

Coaxial

MOV

1 cm

To DSA (1)

To DSA

(1)

1 m

1 m "Span"

w

“A”

O

“B”

Fig. 7. Test circuit for quantifying inductive coupling.

some authors and offered in some commercial packages. Fig. 7

shows the test circuit and definition of the terms “span” and

“w” (width). The test circuit consists of two well-defined

rectangular loops of conductors with the dimensions shown,

mounted on a common sheet of insulating material. On the

left, a loop in which the applied surge current is driven into

the coaxial MOV; on the right, a loop representing the path

of the power supply toward the protected load—in this case,

the voltage input of a digital signal analyzer (DSA). The surge

current imposed on the MOV (maintained at the same level for

all the tests by keeping the same setting on the surge generator)

is monitored by a current-viewing transducer and fed to a

second channel of the DSA. Bonding the conductors of the

two loops at “A” and “B” allows obtaining a configuration

equivalent to that of a conventional two-terminal, one-port,

shunt-connected SPD.

Figs. 8 and 9 (overleaf) show the results obtained with two

different standard surge waveforms—the Ring Wave and the

Combination Wave of C62.41-1991 [9] for fixed dimensions

(1 m) of the surge loop (left square in Fig. 7), and a constant

width but decreasing span of the measurement loop

(right square in Fig. 7). Maximum decrease of the span would

of course be accomplished by twisting the leads that go to the

DSA, immediately from the point of attachment to the MOV.

And the ultimate minimum span is the coaxial cable output from

the MOV.

The oscillograms of Fig. 8 (for the relatively high of a

Ring Wave) show, from left to right, how the inductive voltage

can be reduced by decreasing the “span” of the loop that feeds

power (and the mitigated surge) to the load. For the first of the

oscillograms (at left), the two loops have a portion of the circuit

in common by bonding the two corners of the squares above

(“A”) and below (“B”) the MOV, clearly the worst possible case,

with a relatively large span representing a very poor lead arrangement.

The next oscillogram toward the right shows the case of the

“improved” four-terminal SPD configuration: the resulting protective voltage is only reduced from 624 to 618 V (the three-digit

values being read from the numerical display of the DSA, not

from the oscillograms). That is hardly an improvement, and it

is perhaps below the variability of the repeated surges and digitizing noise.5 This negligible difference between the two configurations demonstrates the fallacy of the four-terminal configuration if not accompanied by attention to the lead dress and

resultant electromagnetic coupling, as can be seen in the oscillograms following these first two. Going on toward the right,

the span is progressively decreased with corresponding decrease

(improvement) of the protective voltage, until the ultimate (but

impractical in the field) idealized configuration of the coaxial

MOV with voltage read from the coaxial cable connection (zero

span and zero loop width, ).

The oscillograms of Fig. 9 show, for a Combination Wave,

and from left to right, the worst case of a large inductive coupling (made equivalent to the common lead configuration by

bonding the corners “A” and “B” of the square loops), the fourterminal coaxial MOV arrangement with a span of 1 m, and the

measurement taken at the output of the coaxial cable.

With that gentler rate of rise (a fifth of that of the Ring Wave

for the current levels injected in this experiment), the effect of

inductive coupling is negligible. (The waveforms are quite similar, only the DSA-generated peak values overwritten in the oscillograms show a difference). Of course, if the amplitude of

the surge current were higher, the effect of the inductive coupling would be higher. Because this inductive effect is linear, in

comparison with the nonlinear voltage-limiting response of the

MOV, it will become increasingly noticeable for higher surge

currents. However, there is a limit to the rate of change

that can be imposed at the sending end of a branch circuit, because the voltage necessary at the sending end for driving such

a steep current toward an SPD at the far end would cause a

flashover of the wiring devices in the service panel [15]).

B. Shunt-Connected SPD Installations

The second experiment demonstrates the effect of installing

a separate shunt-type SPD with long connections to a service

panel. For practical situations, it is often postulated that the connecting leads can be represented by an inductance in the order of

1 , while the resistance of these leads can be neglected.

A connection involving 30 cm of leads, a typical length for a

5The measurements were conducted with calibrated instruments but some

variability occurs in successive shots. The differences observed for the different

span values exceed uncertainties, so that any uncertainties will not affect the

conclusions.
MARTZLOFF AND PHIPPS: LINGERING LEAD LENGTH LEGACIES IN SURGE-PROTECTIVE DEVICES APPLICATIONS 155

Fig. 8. Induced voltage with injected Ring Wave.

Fig. 9. Induced voltage with injected Combination Wave.

careful installation of a shunt-connected SPD,6 could add several hundred volts to the limiting voltage achieved by the SPD

itself in cases of high rates of current changes in the incoming

surge.

SPDs packaged as power strips or plug-in inherently provide

a two-port configuration on which the user has no control, but

hopefully include internal wiring configuration that minimizes

the lead effect. Furthermore, SPDs designed for integrated installation, such as a meter-base SPD or a panel plug-in SPD,

offer a minimum of lead length, if the grounding lead is kept

as short as possible (twisting leads to reduce the loop area or

cancel the coupling is not a possible option in this case). On the

other hand, in the case of separate SPDs permanently connected

in shunt but located some distance from the point of connection,

the length of that connection becomes quite significant, as our

second experiment will show (nothing new about that), but also

quantify.

Again, IEC 61 643-12 provides useful information on this

subject, but its Fig. 10-c (redrawn here as Fig. 10) only states

that twisting leads is an acceptable alternative when the preferred four-terminal configuration (Fig. 5) is not possible. In

our second experiment that we are about to describe, the connection of the SPD was made with the closely-spaced but not

twisted pair of conductors encased in their plastic jacket. We did

6Several IEEE and UL standards now being developed include a stipulation

that the measurement of the limiting voltage shall be performed with a specified

lead length. However, some of these measurements are specified for relatively

low values of the surge current, making it more difficult to detect the significance

of the linear increase for high surge currents.

not attempt to twist the leads, being unaware of a potential significant reduction of inductance by twisting the closely-spaced

pair (unlike sensitivity to external electromagnetic fields which,

indeed, can be decreased by twisting leads). Instead, we went

to another possibly greater reduction of inductance by using a

coaxial cable connection, as we will describe later.

The experiment was conducted with a circuit as shown in

Fig. 11, using a 20-m-long line of typical residential cable

( conductors, plastic jacket, 2.5 or #12 AWG).

The coaxial varistor was connected at the far end (right),

and a Ring Wave was applied at the near end (left). With a

constant generator setting and an unchanged line length, the

surge current could be maintained at a constant amplitude and

waveform, thus allowing direct comparison of the measured

voltages. These voltages were measured for several distances

“d” between the varistor and the point of connection of the

probes. In an actual installation, this point of connection would

be the service panel, and the cable length “d” between that

point and the varistor would be the infamous “lead length”

associated with a real-world installation. Fig. 12 (overleaf)

shows the voltage measured for an ideal (but impractical)

coaxial MOV, serving as baseline reference of the “true” limiting

voltage, and the voltages measured for increasing values of

the lead length.

Fig. 12 shows, from left to right, the voltages at the point of

connection of the MOV (Vp) for increasing distances between

this point of connection and the shunt-connected SPD, the idealized coaxial MOV in our experiment (upper trace). The lower

traces document the constant value of the peak of the impinging
156 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 1, JANUARY 2004

SPD

Fig. 10. Acceptable connection arrangement when four-terminal arrangement

is not possible, per IEC 61 643-12.

Surge

Generator

To DSA (1)

To DSA (2)

20 m

Coax

SPD

“d”

Fig. 11. Test circuit for assessing the effect of lead length.

surge current injected into the circuit. From left to right, compared to the baseline for a measurement made at the

coaxial cable output of the MOV, the Vp caption shows the increase in the effective limiting voltage (decreased performance)

that will be seen by the “protected” load. That increase is already 240 V for just 1 m of connecting leads and that type of

impinging surge.

Some proposals have been made to decrease this adverse effect by using a coaxial cable to make the connection of the SPD

package to the service panel. For the last oscillogram to the right

of Fig. 12, a readily available 3-m length of an RG8 coaxial

cable replaced the last 3 m of the plastic-jacket cable. Interpolating the readings on plain cable for and

yields 1150 V (for a 3-m length of plastic jacketed cable), compared to the 960 V obtained for the coaxial cable connection.7

While this might be seen as a significant improvement, it might

not be large enough to justify the costs or the complication of a

coaxial cable lead that would have to be installed by an electrician unfamiliar with methods of connecting such coaxial cables

within conventional wiring.

The experiments reported here were conducted using real

wiring but contrived configurations to illustrate the points being

made. The applied surges were delivered by a generator producing “textbook” C62.41 waveshapes. Being injected in an inductive circuit, the actual surge current had a rise time of about

0.8 rather than the C62.41 value of 0.5 . Close examination of the original laboratory (larger) current traces of Fig. 12

revealed an actual maximum rate of rise of about 290 for a

peak value of 220 A (about half the 500 A peak value of the Cat7In case our readers would wonder why we used a 3-m length of cable rather

than 2 or 4 m, that would allow a direct comparison with the plastic-jacket

cable (or a conduit-enclosed set of single wires as used in commercial installations), this last experiment with the coaxial cable connection was an unplanned

last-minute addition to the test and was improvised by using an available cable

borrowed from other equipment, for which the careful terminations could not

be tampered with; hence, the nonnegotiable 3-m length—a further illustration

of the inconvenience of making coaxial cable connections in the field.

egory B of C62.41). Such a rate of rise, applied to a connection

of 1 m, and rule of thumb of 1 for the cable inductance,

should produce a voltage drop of about 290 V. The difference

in the observed voltages in Fig. 12 for and

is 240 V, not quite the 290 V computed with the rule of thumb

inductance value. Given the wide range of real-world rates of

rise, this difference between the experimental observations and

the rule-of-thumb computation does not affect the conclusions

on the order of magnitude of the effect.

In the previously cited paper [15], the “gentle toe” concept

was brought up: the theoretical waveforms, such as those used

in numerical computations, can produce unrealistic values for

the maximum rate of rise at the instant of the surge initiation. In

the real world, surge currents do not have their maximum rate of

rise at , but only some brief time after. Another difference

between theory and reality is that most practical Combination

Wave surge generators have an “undershoot”—a reversal of polarity in the surge current—after the theoretical unidirectional

impulse. This polarity reversal is further enhanced by the inductance of practical circuits, as opposed to the dead short postulated in the definition of the short-circuit current of the Combination Wave. Consequently, for modeling purposes, many researchers use a damped sine wave instead of the standard unidirectional wave (Hasse et al. [16]). However, this damped sine

wave has its maximum at (the derivative of the sine

is a cosine); hence, the “gentle toe” idea to reconcile theory and

reality.

For instance, Table I, first compiled in the cited paper [15],

shows the maximum values of for three different nominal

rise times of a damped sine wave with a 5 kA peak. It is noteworthy that the relationships are not linear, and that the maximum is greater than the value that one would obtain by

simply dividing the rise time into the peak value, a fact that

is sometimes overlooked in oversimplified discussions. These

more realistic values of can then be combined with the

empirical 1- value of the connecting leads to estimate the

degradation resulting from an excessive lead length.

IV. CONCLUSION

These experiments have clearly demonstrated that focusing

exclusively on the “lead length” for SPD installations can lead to

misconceptions or unwarranted expectations, such as the “fourterminal SPD” configuration. On the other hand, a quantitative

assessment of the effect of long connections of a shunt-type device will provide useful guidance on installation practices.

1) While there is merit in the concept of a four-terminal

shunt SPD, the benefits can be greatly degraded if proper

attention is not given to the lead configuration. Just using

a four-terminal device will not ensure optimum performance.

2) Improper installation of a separate shunt-type SPD via a

“long” connecting cable to the service panel will degrade

the performance in case of high rates of current changes

in the impinging surge (in particular those implied for

some commercial packages that propose ratings of tens

of thousands of amperes). In the case of more moderate

reasonable rates of change, this effect might have been

somewhat overemphasized in the literature.
MARTZLOFF AND PHIPPS: LINGERING LEAD LENGTH LEGACIES IN SURGE-PROTECTIVE DEVICES APPLICATIONS 157

Fig. 12. Effect of SPD connection length on the protective level of downstream loads.

TABLE I

RELATIONSHIP BETWEEN NOMINAL RISE TIME AND MAXIMUM RATE OF

CURRENT RISE FOR A 5000-A PEAK SURGE CURRENT

Nominal rise time, μs 5 10 20

Maximum di/dt, A/μs 1250 850 630

3) Attention should be given to the lead configuration as well

as to lead length. For instance:

• For a separately-mounted one-port SPD, twisting

the leads or using a coaxial cable between their

point of connection to the protected circuit and the

SPD package will reduce the inductive coupling but

not greatly reduce the inductance of the connection.

Lead length remains a significant factor.

• For one-port SPD packages that are mounted inside

or on the side of a panel, an arrangement that provides a minimum of lead length, twisting leads (if

possible) will help reduce inductive coupling.

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François D. Martzloff (M’56–LF’94) is with the

National Institute of Standards and Technology

(NIST), Gaithersburg, MD, where he has continued

his pursuit of transients. He had 32 years of

experience in the private sector [Southern States

Equipment (Hampton, GA) and General Electric],

before joining NIST in 1985.

As technical contributor, editor, and working

group chair, he contributed to several IEEE, IEC, and

UIE standards and guides, and has published many

research and tutorial papers (such as the present one)

on the application of surge-protective devices and power quality.

Kermit Phipps (M’95) is with EPRI PEAC,

Knoxville, TN, where he is involved in electromagnetic-compatibility (EMC) test programs in

accordance with standards of the IEEE, IEC, U.S.

Military, and UL, as well as with the EPRI System

Compatibility Protocols. He served in the U.S. Air

Force before joining EPRI PEAC.

He has authored several papers on surge protection

and SPD applications, and has conducted a number

of power quality training sessions and field investigations.

Mr. Phipps is Chair of the P1560 Filter Measurement Standard and Secretary

of the IEEE EMC TC-4 Working Group.