Significance 

Part 8 – Coordination of cascaded SPDs 

The early nineties were marked by the emergence of concerns about the coordination of cascaded SPD in the midst 

of “common wisdom” that voltage surges impinging upon the service entrance of a building would inherently become 

less severe as they propagate and divide among the branch circuit of the installation. That perception was reinforced 

by the publication in 1980 of an IEC Standard on insulation coordination that figured prominently a “staircase” of 

descending surge voltage levels. As a result of that perception, proposals were made to provide a service entrance 

SPD with a limiting voltage higher than the limiting voltage of the SPDs installed at the point-of-use receptacles. 

Numerical simulations and measurements on actual SPDs demonstrated the pitfalls of that perception. For an 

effective coordination to occur – service entrance SPD diverting the bulk of the surge current and point-of-use SPD 

mitigation as needed – the service entrance SPD cannot have a substantially higher limiting voltage than the point-ofuse SPD, lest the latter take on the bulk of the energy. The inductance of the wiring between the service entrance 

can add some voltage drop between the two devices, so that an acceptable degree of coordination can still be 

achieved if the two device have equal limiting voltages. 

The redeeming effect of the wiring inductance is of course dependent upon the waveform of the impinging current 

surge, as well as the length of the branch circuit. The relationships of these parameters are explored in the 

computations and experiments reported in the paper. 

Filename: Coordination 1991 
Cascading Surge

Protective Devices: Coordination versus the IEC 664 Staircase 

Montage en cascade de parafoudres: Coordination ou gradins IEC 664 ? 

Fran~ois D . Martzloff 

National Institute of Standards and Technology 

Gaithersburg, Maryianci 20899 

Jih-Sheng Lai 

Power Electronics Applications Center 

Knoxville, Tennessee 37932 

Abstract = cc;-cLAing wo or ,%ore siirgc-pi-o;efiiiic? 

devices located rpsp~cti~-ely rr.f the service e!!trrr!!ce c>f a 

building and near the sensitive equipment is intended to 

ensure that each device shares the surge stress in an 

manner commensurate with its rating, to achieve reliable 

protection of equipment against surges impinging fi-om 

the utility supply as well as internally generated surges. 

However, depending upon the relative clamping voltages 

of the two devices, their separation distance, and the 

waveform of the impinging surge, coordination may or 

may not be effective. Ihe paper reports computations 

confirmed by measurements of the energy deposited in 

the devices for combinations of these three parameters. 

Introduction 

Recent progress in the availability of surge-protective 

devices, combined with increased awareness of tine need 

tc ,W,t~,f PP"'.;t-.rC. on... ---4 -:--4 ------- yaws- ovuirarlve c.yu;jjulurr iiga~uar aulgoa, hi~ 

prompted the app!ication of 2 millti-ct~n ...-... ---r racraAm ----- 

protection scheme. In this scheme, a high-energy surgeprotective device is installed at the service entrance of a 

building to divert the major part of the surge energy. 

Then, surge-protective devices with lower energyhandling capability and lower clamping voltage than that 

of the service entrance, are installed downstream near.or 

Somiiiaire - ie morrircge ell cascade de piusieu

. , ,~grgJ~~2drcs, ~ez~~giye::;e;;[ & !'o;.F;ysc &Iii sefie*';. 2: c

voisinage du martriel ri prortger est envisqt dms IP h

d'rrrsurer que chaque dispositifprenne une part de 

contrainte totale associte au transitoire qui correspond

bien ci la valeur norninale de chacun. Cette dispositio

permet d'assurer la3abiliti de la protection contre l

transitoires d'origine exttrieure aussi bien que ceu

produits par le rnattriel adjacent. Cette communicatio

donne les risultats de calculs, con)rmts par d

mesures, pour un ensemble de niveaux d'icri?ta

relatifs, de distances stparant les dispositfs, et de 

forme d'ottde postulte pour le transitoire. 

This scenario was initially based on the technology 

secondary surge arresters prevailing In the 1970s an

early 1980s, as well as on the consensus concerning t

waveform and current levels of representative lightni

surges impinging on a building service entrance. Wi

the emergence of new types of arresters for servi

entrance duty and the recognition of waveforms wi

greater duration than the classic 8/20 FS impulse, a ne

situation arises that may invalidate the expectations o

the cascade coordination scenario. 

at the euui~ment and com~lete the ~rotection. Service entrance arresters were generally based on th

. . To make the distinction between these two devices, we 

will call the service entrance device 'arrester' and the 

downstream device 'suppressor'. Such a scheme is 

described as 'coordinated' if, indeed, the device with 

high energy handling capability receives the largest part 

of the total energy involved in the surge event. 

combination of a gap with a nonlinear varistor elemen

the classic surge arrester design before the advent 

metal-oxide varistors (MOV) that made gapless arreste

possible. With a gap plus varistor element, the servi

entrance arrester could easily be designed with a 175-

Maximum Continuous Operating Voltage (MCOV) in 

120-V (rms) system. The downstream uppressers we
selected with a low level, driven by the perception that 

sensitive equipment requires a low protective level 

[I]. The scheme can work if there is a series 

impedance (mostly inductance) between the arrester and 

the suppressor, because the inductive drop in the series 

impedance, added to the clamping voltage of the 

suppressor, becomes high enough to sparkover the 

arrester gap. Thereafter, the lower discharge voltage of 

ihe arrester (made possibie by the gap) ensures that the 

,,.,, ,,A ,F rL,. -..--- ..a& "I ILL= ~UI~E: F;IK;L~Y is diverted by the 

arrester, relieving the suppressor from the heavy duty 

121. 

This concept was in complete harmony with the 

'Installation Category' concept of IEC Pub 664-1980 

[3] which featured a descending staircase of voltages, 

starting with the 'uncontrolled situation' at the building 

service entrance, with several lower levels within the 

building (Figure 1). The lower levels would be 

achieved, according to IEC 664, by means of the natural 

attenuation caused by the multiple branch circuits, or by 

a deliberate interface - a surge-protective device. 

Figure 1 

Installation Categories according to 

!EC Pik 664-1 983 [31 

On the other hand, the ANSIIIEEE C62.41-1980 Guide [4] 

(updated as a Recommended Practice in 1991) defined a 

set of 'Location Categories' within a building. 

According to that concept, constant voltage levels are 

maintained downstream of the service entrance, but the 

current levels decrease. That concept was based on 

recognition that the wiring inductance would decrease 

the available surge current at locations deeper into the 

building - for the 8/20 ps current waveform then 

universally postulated to be representative. Thus, the 

stage was set for a mind-set of decreasing surge energy 

as the wiring progresses through the building, away 

from the service entrance. 

The new situation 

With the emergence of MOV-based, gapless arresters, 

a new situation has been created. The Maximum 

Continuous Operating Voltage of the arrester will 

deternine its r.!aqir?g !eve!. SO= nti!ities wish !G 

ensure survival of the arrester under the condition of a 

lost neutral, that is, twice the normal voltage for a 

single-phase, three-wire service connection. For threephase systems in which devices are connected between 

phases and ground (protective earth), the usual practice 

is to rate these devices for the line-to-line voltage in 

order to provide for the case of one comer of the delta 

being at ground, or the case of undefined voltage 

between neutral and ground. 

This survival wish is a motivation for selecting an 

arrester clamping voltage corresponding to 1.7 to 2 

times the single-phase voltage. Meanwhile, if singlephase equipment, typical of home electronic systems 

('domotique' in French) are perceived to be sensitive, 

there will be a tendency to protect them with the lowest 

possible clamping voltage. 

This sibatim sets the stage hi 'p:-L lIgLI-LuW T -.-.

combination where the arrester c!amping vr?!tage is 

higher than that of the suppressor [51. During the 

ascending portion of a relatively steep surge such as the 

8/20 ps, the inductive drop may still be sufficient to 

develop enough voltage across the terminals of the 

arrester and force it to absorb much of the impinging 

energy. However, during the tail of the surge, the 

situation is reversed; the inductive drop is now negative 

and thus the suppressor with lower voltage, not the 

arrester, will divert the current. 

For the new waveforms proposed in C62.41-199 1 [6], 

this situation occurs for the 10/1000 ps where the tail 

contains most of the energy, and the relief provided by 

the arrester might not last past the front part of the 

surge. An alternate means has been proposed - 

'hw-Eigh' where the arrester c!mpi~g ve!tage is !aver 

than that of the suppressor [7],[8!. Th_us, a 

disagreement has emerged among the recommendations 

for coordinated cascade schemes: the 1970-1980 

perception and Ref [5] suggesting a 'High-Low' and the 

new 'Low-High' suggestion of Refs [7] and [8]. 

This paper reports the results of modeling the situation 

created by the emergence of gapless arresters and longer 

waveforms, with the necessary experimental validation

These results cover a range of parameters to define the 

limits of a valid cascade coordination, and will serve as 

input to the surge protective device application guides 

now under development by providing a reconciliation of 

the apparent disagreement, which is actually rooted in 

different premises on the coordination parameters. 
MOV Circuit Modeling 

The current-voltage (I-V) characteristic of a MOV has 

long been represented by a power law, i. e., I = k VOL 

[9]. This equation is only applicable in a certain 

ve!kgp (ccrre2t) rwxg:: in wbdCh the I-V charac&i;ls:ic 

presents a linear relationship in a !og-!ng p!nt. Fnr !he 

high-current region of the characteristic, the current 

increment rate starts dropping. This change appears on 

the I-V plot as a voltage upturn in the high-current 

region. A modified I-V characteristic is proposed here 

as expressed in (1). 

1 = , - (V - Vo) [A - !: (V - V0)l (1) 

The coefficients in (1) can be obtained from a curve 

fitting technique by minimum-error-norm [lo] using 

a MOV data book [9] or experimental results. The 

parameter k and exponent a can be obtained from fitting 

the data in the linear log-log region. The exponential 

term is added to cover the voltages higher than a 

threshold voltage Vo where the upturn begins and can be 

obtained hm f tting the I-V chz~?.~teT;Istics i:: !he higher 

current (voltage) region. Using (1): the MOV circuit 

model can then be simply represented by a voltagedependent current source. 

Model parameters in (1) can be obtained from the MOV 

data book and verified by experiments. The exponent a 

in this model is a function of the MOV voltage rating. 

The threshold voltage Vo and coefficients X and ( are 

.functions of the voltage rating and the size. Table 1 lists 

the curve fitting data for the equivalent circuit 

parameters of three MOVs typical of what might be 

considered for a 120-V power system: 130 V for 'low', 

150 V for 'medium', and 250 V for 'high'. For 

European systems with a 220-V single-phase voltage, 

similar ratings would be 250 V for a 'low', 320 V for a 

'medium', and 420 V for a 'high'. Note that the 

numerical values of the parameters are unitdependent, 

and are given in Table 1 for units in volts and amperes. 

Table 1 

Curve fitting results for three 20-mm dia MOVs 

Rating k a A I < IVOCV) 

130V (4.0*10-~~( 30 10.05118*10-~1 320 

In Figure 2, the marked points are the data directly read 

from curves in the MOV data book, while the three linesare a plot of the computed I-V characteristic &cording 

to (I), using the parameters listed in Table 1. Note the 

remarkable fit achieved by this model over the range of 

interest. 

Peak Currenl (A) 

Figure 2 

MOV characteristics obtained from modeling 

results 

There is a tolerance of +_ 10% on the actual value

within a given varistor rating. Figure 2 shows th

maximum clamping voltage levels; a device at the lo

end of the tolerance band would have a characterist

20% lower than the data book characteristics. In fac

the two closely rated cascaded devices (130 V and 15

V) could in some extreme cases become inverted in th

sequence, 'Low-High' becoming in reality 'High-Low

as 130 x 1.1 = 143 and 150 x 0.9 = 135. 

Furthermore, results (presented below) show that for th

250-150 combination, the difference is so large that 

low-end 250 (225 V) combined with a high-end 150 (16

V) would not make an appreciable difference in th

energy sharing. Thus, the simulation computations wer

performed for all three devices at their nominal value

with appropriate modification of the parameters in th

model equation. 

Simulation of Cascaded Devices 

in a Low-Voltage System 

Figure 3 shows a typical two-stage cascade surg

protection. The arrester and the varistor are separate

by a distance d determined by the specific installation

I I 

/ I i /I 

J 112 wires 

- Location Location 

Categoly B Category A 

Figure 3 

Configuration of a two-stage cascade 
Four different d values, 5 m, 10 m, 20 m, and 40 m 

were used in the simulation, with a #12 AWG (1.83-rnm 

dia.) wire, representative of U.S. practice for 20 A 

branch circuits. At the frequencies involved in the 

surges considered, inductance is the dominant parameter 

and the wire diameter plays only a minor role [ll]; 

so that the resistance of the wire could be neglected. 

However, given the flexibility of the model, it was 

inciuded. 

The complete simulation model, shown in Figure 4, 

consists of a surge source IG, two voltage-dependent 

current sources IA and IS, and a line impedance between 

the two current sources. For three device voltage levels, 

there is a total of nine possible cascade combinations as 

shown in Table 2. 

Simulation and Experimental Results - 8/20 Wave 

As one example of the combinations that were 

simulated, consider a cascade with 250 V and 130 V 

devices separated by 10 m. The simulation results of 

the currents flowing in the two devices are shown in 

Figure 5, where it is the iotai current injected into the 

cacade bj the surge souice of the il is the 

arrester current, I2 is the SE~~TPUSSC: c~r:ent

Figure 6 shows the corresponding device clamping 

voltages, V1 and V2 across the arrester and suppressor 

respectively. Figure 7 shows instantaneous powers PI 

and P2, respectively for the arrester and the suppressor. 

By integrating the instantaneous power, the energy 

deposited in the arrester and the suppressor were 

calculated as 29.7 J and 8.6 J respectively. 

Table 2 

Nine cascade combinations for three devices 

Suppressor 

250 V 150 V 

I( 130 V 

250 V 

II 

ll 

150 V 

1 

150 V 

11 

130 V 

130 V 

Two standard waves from Ref [6] were chosen: the 

1.2150 ps - 8/20 ps Combination Wave, and the 10/1000 

ps Impulse Wave. For four distances, two waveforms, 

and nine cascade combinations, a total of 72 cases are 

reported here. The case of the 100 kHz Ring Wave was 

also simulated and tested 1121, but is not reported 

here because the low energy stress involved in that 

waveform will not deposit substantial energy in the 

rippressor or the arrester. 

Figure 5 

Simulated current responses for 250 V - 130 V 

cascade, 10 m separation, 8/20 ps applied surge 

1200 

BW 

- 403 

- > 

> 0 

433 

-0w 0 10 20 30 40 M 80 70 80 W 100 

t (us) 

Figure 6 

Simulated voltage responses for 250 V - 130 V 

cascade, 10 m separation, 8/20 ps applied surge 

2500 

2M-m 

-1m 

- 5 

loo0 

500 

0 I I I I I I 1 0 10 20 3(3 40 M 60 70 80 90 100 

t (us) 

Figure 7 

Simulated dissi~ated Dower for 250 V - 130 V 

cascade, i 0.m sedaration, 8/20 /IS surge 
Table 3 lists the computed results for the 8/20 Wave 

simulation, as energy deposition in the arrester (A) and 

suppressor (S) for all the combinations of different High 

(250 V), Medium (150 V), and Low (150 V) devices as 

arrester and suppressor. 

Table 3 

Energy deposition in the cascaded devices 

with a 3-kA 8120 Wave as the surge source. 

Energy deposited in each device (joules) as a 11 Rating of I function of separating distance (meters) 

Figure 8 shows in graphic form the results of Table 3, 

where the lines represent the energy deposited in the 

suppressor as percentage of the total surge energy, as a 

function of relative clamping voltages and separation 

distance. With the scale used in the figure (geometric 

distance), the curves are approximately straight lines 

over the range. For the High-Low condition, the energy 

deposition in the suppressor decreases rapidly when the 

separation distance increases. This result explains how 

the High-Low configuration can achieve a good 

coordination with the 8/20 Wave, provided that there be 

sufficient distance between the two devices, as stated in 

Ref [S]. 

When the distance between twn devices Is E~IICPL!, !he 

energy deposition tends to increase in the suppressor and 

decrease in the arrester. This decrease occurs because 

the line inductance does not provide enough voltage drop 

(L di/dt), and the low clamping voltage of the suppressor 

reduces the voltage across the arrester, and thus reduces 

the energy deposition level. The total energy deposition 

in the two devices also varies with the distance for the 

High-Low configuration. In Table 3, the total energy 

deposition for the 250-250 combination is near constant 

at 103 J for different distances. However, for 250-150 

and 250-130 combinations, the total energy deposition 

decreases when the distance is reduced, because the 

suppressor tends to lower the voltage across the arrester. 

This situation can be explained by the fact that the 

impinging surge is defined as a current source, so that 

offering it diversion through a device with higher 

clamping voltage results in higher energy deposition. 

H-M 

H-L \ 

"-"\ \ 

M-M \\ \\ 

L-L,\ \ 

M-H 

LH I I I 

5 10 20 40 

DISTANCE BETWEEN ARRESTER 

AND SUPPRESSOR (m) 

Figure 8 

Relative energy deposited by an 8/20 ps Wave 

in the suppressor for arrester-suppressor 

combinations of 250 V (HI, 150 V (M), or 130 V 

(L! ratings, as a functiny! ~f separation distance 

For Low-High configurations such as 150-250 an

130-250 cases, the higher voltage suppressor receive

a:mosi zeio energy. Tine use of the suppressor is nea

redundant in this case, except for its application t

mitigate internally generated surges. With closely rate

devices (130-150), the 150-V voltage suppressor als

receives much less energy than the 130-V arrester. 

Now turning to measurements, the same cascad

configuration, 250 V - 130 V with 10-m separatio

(Figure 3), was injected with a surge produced by 

Combination Wave generator. The surge generato

delivers an approximation of the standard waveform

consequently, the waveforms obtained from th

experiment are not exactly the same as the simulate

waveforms. However, the power distribution betwee

the two devices shows good agreement between th

simulation and the experiment. 

Figure 9 shows the experimental results obtained with 

cascade of two devices, 250 V and 130 V, with 10 m o

separation. Oscillograrns were recorded for the curren

voltage and power in the two devices, where th

subscript 1 corresponds to the arrester and the subscrip

2 to the suppressor. The goal was to produce a 3 kA 

impinging surge (I1 + IZ), but a slightly higher curren

(3.3 kA instead of 3 kA in the simulation) wa

produced, typical of the sensitivity of nonlinear circuit

to minute changes in the applied voltage. The energ

deposited in each device was computed by integration o

the power (performed by the oscilloscope): 33.8 J in th

arrester and 11.1 J in the suppressor: To compar

simulation and measurement, prorating the simulatio

results (from Figure 7) to 3.3 kA would yield 32.7 J an

9.5 j rcspeciiveiy, a satisfactory agreement. 
1, + 12: 1000 Aldiv 

Il : 1000 Aldiv 

It + 12: 1000 Aldiv 

12: 1000 Aldiv 

(a) Arrester 

(b) Suppressor 

Figure 9 

Experimental results for the 250 V-130 V, 10-m 

apart cascade condition. 

Compared to the 8/20 Wave, the 1011000 Wave has a 

slower and longer drooping tail that contains most of the 

surge energy. During the long tail period, the inductive 

voltage drop between the arrester and the suppressor is 

low, and the voltage appearing across the arrester is 

reduced by the effect of the suppressor even with long 

distances between the two devices. Thus, the High-Low 

configuration cannot be coordinated as the high-voltage 

arrester will not absorb any impinging energy, but the 

suppressor does. Figures 10, 11 and 12 show the 

computed current, voltage, and power for the arrester 

and for the suppressor under a High-Low (250-130) 

simu!ation hi a 2%-A p~k surge ciiiieiii. 

The high-voltage arrester clamps the voltage during the 

impulse rising period and draws a small amount of the 

current pulse, 11, which is almost invisible in the 

computer-generated plot of Figure 10. The power 

dissipated in the arrester, PI, is also a small pulse that 

appears at the rising period as shown in Figure 12. The 

low-voltage suppressor absorbs all the impinging energy 

in this High-Low configuration, defeating the intended 

coordination. 

0 0.2 0.4 0.6 0.8 1 12 1.4 1.0 1.8 2 

t (m) 

Figure 10 

Sirnuiated current responses for 250 v - 130 v 

cascade, ? 0 m separation, ?0/? 000 i;s sijigs 

0 0.2 0.4 0.6 0.8 1 12 1.4 1.8 1.8 2 

t (m) 

Figure 11 

Simulated voltage responses for 250 V - 130 V 

cascade, 10 m separation, 1011 000 ps surge 

0 0.2 0.4 0.6 0.8 I 12 1.4 1.6 1.8 2 

t (a) 

Figure 12 

Simulated dissipated power for 250 V - 130 V 

cascade, ! C! .rl? separatlen, ! 0/! 000 ;.s surge 
Table 4 lists the simulated energy deposition in the 

cascaded devices for different High-Low and Low-High 

combinations and for different distances. Figure 13 

presents in graphic form the results of Table 4, with 

lines showing the energy deposited in the suppressor as 

percentage of the total surge energy, as a function of 

relative clamping voltages and separation distance. 

iabie 4 

Energ.; deposi$on in :f;e eascadeS devices 

a 220-A, 10/1000 Wave as the surge source. 

Energy deposited in each device (joules) as a 11 Rating I function of seoaratina distance (meters) 11 

H-L 

H-M 

L-M 

M-H I I I I L-H 

5 10 20 40 

DISTANCE BETWEEN ARRESTER 

AND SUPPRESSOR (m) 

Figure 13 

Relative energy deposited by a 1011 000 ps Wave 

in the suppressor for arrester-suppressor 

combinations of 250 V (H), 150 V (MI, or 130 V 

(L) iaiiiigs, as a tinction of separation distance 

It can be seen from Table 4 that the lowvoltage devic

always absorbs higher energy than the high-voltag

device. This situation exists because the voltage acros

the high-voltage device is clamped to the same level a

that of the low-voltage device, and thus the energy i

diverted to the device having the lower clamping voltage 

of the pair. 

Unlike the case of the 8/20 Wave, coordination for th

10/1000 Wave can only be achieved by Low-High

Medium-High, or Low-Medium. Equally rated device

(250-250, 150-150, and 130-130) result in 50 % of th

surge energy being deposited in the suppressor, not a 

very good coordination. Note that with two devices o

equal nominal value, but random tolerance levels, it i

possible that the relative tolerances might in fact produc

a situation which would not achieve good coordination

for instance, an effective 150-130 combination can resul

from tolerance shifts in an intended 150-150 or 130-13

pair. This shift would impose a 70-J duty to th

suppressor and only 7 J to the arrester, in the case o

5-m separation. 

?l?e experiment.! respesse ts a !O!!W Wave, fx 

Low-Medium configuration is shown in Figure 14 wher

I, and I? are the currents flowing in the 130-V arreste

aid the-150-V suppressor respectively. This figur

shows an example of good coordination by 

Low-Medium, where most of the surge energy i

absorbed by the low-voltage arrester, and little surg

current propagates into the building - one of the goals o

the two-step coordinated approach. The arrester voltag

V1 is almost the same as the suppressor voltage V2 wit

a slight difference at the beginning of the surge. 

Figure 14 

Experimental results for a 130 V - 150 V, 10-m 

apart cascaded cmditien with ! 0!! 000 Wave. 
Discussion 

The benefit from a coordinated approach is to allow a 

single device at the service entrance to perform the 

high-energy duty, while several smaller devices within 

the premises can perform local suppression. This 

arrangement avoids !he flow nf !xge surge currmh k 

the branch circuits of the installation, a situation known 

to produce undesirable side effects [13]. 

On the other hand, the situation exists where millions of 

small suppressors have been installed within equipment 

or as plug-in devices, with only sporadic and anecdotal 

reports of problems. Thus, it is evidently possible to 

obtain protection with suppressors alone, while a 

coordinated scheme would provide additional benefits 

and eliminate side-effects. 

Some utilities wish to provide a service-entrance arrester 

capable of withstanding the 240-V overvoltage that can 

occur on the 120-V branches when the neutral is lost. 

This desire will force the coordination scheme into a 

High-Low situation because of the uncontrolled 

installation of low clamping voltage suppressors by the 

occupr;?: of :he preinises. resiiiu of the simuiation 

and wperimenb! mearurezents shew that the ~bjective 

of coordination could still be achieved with a 250-130 

combination, as long as some distance is provided 

between the two devices, and as long as long waves such 

as the 1011OOO pi are not occumng with high peak 

values. This proviso provides an incentive for obtaining 

better statistics on the occurrence of long waves. 

ANSIIIEEE C62.41-199 1 141 recommends considering 

these long waves as an additional, not a standard 

waveform. Thus, the determination of a successful 

coordination depends for the moment on the perception 

of what the prevailing highenergy waveforms can be for 

specific environments. 

Conclusions 

1. Coordination of cascaded devices can be achieved 

under various combinations of parameters, but some 

combinations will result in having a suppressor with low 

energy-handling capability called upon to divert the 

largest part of the surge energy. This uncoordinated 

situation can create adverse side effects when high 

current surges occur. 

2. Significant parameters in achieving successful 

coordination involve three factors, over which the 

occupant of the premises has no control: the relative 

clamping voltages of the two devices, their separation 

distance, and the prevailing waveforms for impinging 

surges. This uncontrolled situation presents a challenge 

and obligation for standards-writing groups to address 

the problem and develop consensus on a trade-off of 

advantages and disadvantages of High-Low versus 

Low-High. 

3. Coordinated schemes can be proposed by utilities to 

their customers, including a service entrance arrester and 

one or more plug-in devices to be installed for the 

dedicated protection of sensitive appliances. However

even such an engineered, coordinated arrangement could 

be defeated by the addition of a suppressor with a very 

low clamping voltage, not an insignificant likelihood in 

view of the present competition for lower clamping 

voibges. 

REFERENCES 

Martzloff, F. D. and Leedy, T. F., Selecting 

Varistor Clamping Voltage: Lower Is Not Better

Proceedings, 1989 Ziirich EMC Symposium. 

Martzloff, F. D., Coordination of Surge Protectors 

in Low-Voltage AC Power Circuits, IEEE 

Transactions PAS-99, JanuaryIFebruary 1980, pp 

129-133. 

IEC Publication 664-1980 Insulation coordination 

within !ow-vo!hge systp~s, inc!nding c!earmces 

and creepage distances for equipment. 

IEEE C62.41-1980, IEEE Guide nn Ssrge Vo!t.nes b 

in Low-Voltage AC Power Circuits. 

Stringfellow, M. F. and Stonely, B. T., 

Coordination of Surge Suppressors in Low-Voltage 

AC Power Circuits, Proceedings, Open Forum on 

Surge Protection Application, June 199 1. 

IEEE C62.41-1991, IEEE Recommended Practice 

on Surge Voltages in Low-Voltage AC Power 

Circuits (To be published September 1991). 

IEC 64lWG3 138A, Explanation of interfaces for 

overvoltage categories - Supplement to Appendix B 

of Report 664, November 1990. 

Standler, R. B., Coordination of Surge Arresters 

and Suppressors for Use on Low-Voltage Mains

Prncedings, 1991 Ziirich EMC Syfipsium. 

T~,,.,~;~..+ II,I+~ .- - -.-- n--.:--- .-.a.v... . vlwgr. SL~~-~JD;VII UGVILG~, Earrib 

Carpi 1991. 

[lOILuenberger, D. G., Linear and Nonlinea

Programming, Addison-Wesley Pub. Co., Reading

Massachusetts, 1984. 

[ll] Martzloff, F.D., On the Propagation of Old and 

New Surges. Proceedings, Open Forum on Surge 

Protection Application, 1991, pp 19-28. 

[12] Lai, J.S. and Martzloff, F.D., Coordinating 

Cascaded Surge-Protective Devices, Proceedings

IEEEIIAS Annual Meeting, October 1991. 

[13] Martzloff, F. D., Coupling, Propagation, and Sid

Effects of Surges in an Industrial Building Wiring 

System, IEEE Transactions IA-26, MarchlApri

i nnn rryv, pp. 193-203.