François D. Martzloff 

General Electric Company 

Schenectady NY 

f.martzloff@ieee.org

Reprinted, with permission, from IEEE Transactions on Power Apparatus and Systems, PAS-99, Jan 1980 

First presented at IEEE Summer Meeting, Vancouver, July 1979

Significance: 

Part 4 – Propagation and coupling of surges 

Part 8 – Coordination of cascaded SPDs 

This paper presents a summary of two earlier and detailed proprietary General Electric reports describing 

experiments conducted in Schenectady NY and in Pittsfield MA, respectively by Martzloff and Crouch. (These 

have now been declassified by General Electric and are included in this Anthology – see Coordination 1976

and Propagation 1978.) The prime purpose of that paper at the time was to report in a non-classified 

platform experimental results that could be useful for the development of IEEE Std 587 (later known as IEEE 

Std C62.41).

In the first experiment, a simple test circuit of two branch circuits originating at a typical service entrance pape

was subjected to relatively high-energy unidirectional impulses, with various combinations of surge-protective 

devices installed at the service panel and/or at the end of the branch circuits. That 1976 experiment was the 

beginning of recognition of the “cascade coordination” issue that became the subject of intense interest in the 

80’s and 90’s (see the listing of contribution by many authors in Part 1, Section 8). 

In the second experiment, the coupling and subsequent propagation of surges was investigated in a more 

complex circuit that included a distribution transformer, service drop, entrance panel, and several branch 

circuits. The surge was injected in the grounding system, not into the phase conductors. This 

experiment thus brought new evidence that ring waves can be stimulated by unidirectional surges. 

Nevertheless, the threat was considered at that time as a surge impinging onto the service entrance from the 

utility, not resulting from a direct flash to the building grounding system. On that latter subject, see Dispersion

and Role of SPDs. 

This paper received the 1982 Paper Award from the Surge-Protective Devices Committee. 

Filename: Coordination 1980
Reprinted by permission of the Institute of Electrical and Electronics Engineers from: 

IEEE Transactions on Power Apparatus and Systems, Vol. PAS-99. No. 1 Jan./Feb. 1980 

COORDINATION OF SURGE PROTECTORS IN LOW-VOLTAGE AC POWER CIRCUITS 

F.D. Martzioff, Member, IEEE 

General Electric Company 

Schenectady, NY 12345 

- Surge protectors can be installed in low-voltage ac power systems 

to limit overvoltages imposed on sensitive loads. Available devices offer a 

range of voltage-clamping levels and energy-handling capability, with the 

usual economic trade-off limitations. Coordination is poss~ble between lowclamping-voltage devices having limited energy capability and high-clampingvoltage devices having high energy capability. The paper gives two examples 

ofcoordination, as well asadditionalexperimental resuitson surge propagation. 

1. INTRODUCTION 

Surge voltages occurring in low-voltage ac power circuits have two origins: 

external surges, produced by power system switching operation or by lightning, 

and internal surges, produced by switching of loads within the local system. 

Typical voltage levels of these surges are sufficient to cause the failure of sensitive electronic appliances or devices, and high surges can cause the failure 

of rugged electromechanical devices (clocks, motors, and heaters) [I ,2]. 

For many years secondary surge arresters from a number of manufacturers 

have been available. These arresters are effective in protecting nonelectronic 

devices against the high-voltage surges associated with lightning or power system switching. However, the voltage allowed by an arrester is st111 too high for 

sensitive electronic devices. Furthermore, installation requires an electrician 

to connect thedevice on hot terminals. 

The advent of the metal oxide varistor packaged as a convenient plugin 

device or incorporated into the appliances makes possible a voltage clamping 

which is more effective than that of the conventional secondary arrester. However, ihe energyhandling capability of such packages is lower than that of an 

arrester, so that large currents associated with lightning strikes cannot be 

handled by these packages. 

The availability of these two different types of suppressors now makes it 

possible to obtain a coordinated protection of all the appliances in a home or 

all the equipment in an industrial environment. Improper coordination, however, could force the lower voltage device to assume all the current, leaving the 

high-energy protector uninvolved; this situation could then cause premature 

failure of the low-voltage suppressor. This paper discusses the elements of a 

coordinated protectivesystem based on experimentation. 

11. SECONDARY ARRESTERS AND LOW-VOLTAGE 

SUPPRESSORS 

Typical secondary arresters for 120 V service consist of an air gap in series 

with a varistor made of silicon carbide. The device is generally packaged with 

two arresters in the same housing; the physical arrangement is designed for installation on the outside of a distribution panel, through a knockout bole of 

the panel enclosure or at the entrance to the building. 

Limitations on the gap design imposed for the purpose of reliable operation and clearing after a high current discharge (10 kA, 8 x 20) do not allow the 

sparkover of the gap to be less than about 2OOO V. This sparkover and the 

time required to achieve it allow injection of a potentially damaging surge into 

the "protected" power system downstream from the arrester: While this 

2000 V level provides better protection than the protective characteristics indicated in ANSI standards [3], lower voltage clamping is desirable for the 

protection of sensitive electronics. 

*In this paper the high-energy suppressor, typically installed at the service 

entrance, will be called arrester. The low-energy, low-voltage suppressor, 

typically installed at an ourlet or incorporated into an applianceor connected 

load, will be called suppressor. 

F 79 635-4 A paper recamended and approved by the 

IEEE Surye Protective Devices Cornnittee of the IEEE 

Power Engineering Society for presentation at the IEEE 

PES S-r Meeting, Vancouver, British Coldia, 

Metal oxide varistors suitable for I20 V line applications can clamp surge 

voltages at less than I000 V, typically at 500 to 600 V for surge currents of less 

than 1000 A. These varistors provide excellent protection for electronic systems. The economics of device size, however, limits the wlde use of large varistors, especially since smaller varistors can do an acceptable job if they are not 

exposed to excessive currents. Proper coordination among the devices used 

is required to obtain a reliable protect~on system. 

111. PROTECTION COORDINATION 

While the installation of surge protective devices functions effectively for 

high-voltage utility systems coordinated by centralized engineering, tbecurrent 

trend toward regulatory installation in low-voltage systems, because they are 

seldom centrally engineered and coordinated, can result in damaged equipment and system failure. The successful application of protective devices to a 

low-voltage system demands a perspective of the total system, as well as a 

knowledge of individual device characteristics. Where such knowledge and 

coordination are lacking, a low-voltage suppressor installed in conjunction 

with an arrester can prevent the voltage at the terminals of an arrerter from 

reaching its sparkover level. As a result, all of the surge current may be forced 

into the suppressor, wh~ch may not have been intended to withstand extreme 

conditions. 

Proper coordination in an arrester/suppressor system requires some impedance between the two devices. This impedance is generally provided by the 

wiring: at the beginning of the surge, the rapidly changing current produces 

an inductive voltage drop in this wiring, in addition to the drop caused by the 

resistanceof the wiring. Thus, thevoltageat theterminalsof thearrester during 

the current rise of the surge is equal to the clamping voltage of the suppressor, 

plus the voltage drop in the line (tests reported below indicate that this voltage 

drop is indeed appreciable). This voltage addition can then raise the terminal 

voltage of the arrester sufficiently to reach sparkover. In this way the arrester 

will divert most of the surge current at the entrance, rather than permitting it 

to flow in the suppressor. 

The application of a suppressor alone is likely to occur because electronic 

appliance manufacturers increasingly provide suppressors incorporated into 

their products. With no arrester at the service entrance, the wiring clearances 

can become a voltage-limiting device, thus establishing a clearance/suppressor 

system. The suppressor would again tend to assume all of the surge current 

flow. The voltage drop in the line, in a manner similar to that of the arrester/ 

suppressor system, would raise the voltage at upstream points to levels that 

may spark over the clearances of wiring devices, providing unplanned rehef 

for the suppressor. When sparkover of the clearances occurs. there are three 

possible results: 

a. A power-follow current occurs, with destructive effects on the 

components. 

b. A power-follow current occurs, but overcurrent protection (breaker 

or fuse) limits the damage. The system can be restored to operation 

after a mere nuisance interruption. 

c. No power-follow current takes place; the overvoltage protective 

function of the system can be considered as accomplished. 

The concept of protecting solid insulation by allowing clearances to spark 

over first is actively promoted by the Low Voltage Insulation Coordination 

Subcommittee of the International Electrotechnical Commission [4]. 

Further discussion of it is outside the scope of the present paper; nevertheless, 

the concept is worth attention because cost reductions and system reliability 

could be obtained through its proper application. 

Two examples of protection coordination will now be discussed in detail. 

These examples represent two scenarios on surge injection; they are based on 

experiments involving an arrester and suppressors in simulated lightning surge 

conditions. In the first scenario the surge is assumed to be ~njected between 

one of the phase wires and the center conductor (ground) of the service entrance. In a second scenario the surge current is assumed to be injected directly 

into the ground system of a service entrance only. Both experiments show the 

benefits and importance of proper coordination. In both tests the arrester was 

a gap-silicon carbide combination (Fig. I) and the suppressor, a metal oxide 

varistor in a plugin package (Fig. 2). 

IV. SURGE APPLIED BETWEEN PHASE AND GROUND 

Test Circuits 

The test circuit (Fig. 3) consisted of a terminal board from which two lines, 

one 7.5 m (25 ft )long and the other 30 m (100 ft) long were strung in the test 

area. A short, 3 m (10 ft), line simulated the service drop. All of these lines 

Canada, July 15-20, 1979.~~~~~~~i~t submitted February 6, were made of three-conductor, nonmetallic. #I2 AWC sheath wire. The new 

1979; made available for printing April 3, 1979. tral and ground wires of the three lines were connected together at the terminal 

board and from there to the reference ground of the test circuit. 

0018-9510/80/0100-0129$000075@ I980 IEEE 
(a) (b) 

Fig. 4. Open-circuit voltage and short-circuit current (without any protecto

Fig. 1. Typical arrester for service entrance installation. 

Fig. 2. Typical suppressor for plugin installation. 

GR~EN 

IGROUNDl 

Fig. 3. Test circuit. 

All surge currents were applied between the line conductor (black) at the 

end of the service drop and the reference ground (green and white). These 

impulses were obtained from a 5 pF capacitor charged at a suitable voltage 

and discharged into the wiring system by an ignitron switch. The resultant 

open-circuit voltage waveform, a unidirectional wave of 1 ps rise time x 50 ps 

to one/half value time, corresponds to the standard test wave in utility systems. 

Fig. 4 shows typical open-circuit voltage and short-circuit current waveforms. 

Voltages were recorded by a storage oscilloscope through an attenuator probe 

(1000:l); currents, through a current probe and a current transformer. Thus, 

the calibrations displayed on the oscillogram are to be multiplied by 1000 for 

the voltage. The current traces show the 50 mV setting corresponding to the 

rated output of the current probe, with the amperes per division shown in 

parentheses corresponding to the current transformer ratio and current probe 

input setting for a direct reading. The sweep rate is also shown on the oscillograms, at IOps/div. for all the tests. 

Test Results 

Fig. 5a shows the voltage across the arrester when subjected to the surge defined by Figs. 4a and 4b. Note that the sparkover voltage reaches 2200 V, with 

several oscillations, before the voltage settles down to the impulse discharge 

voltage at about 2000 V at its start. 

Figs. 5b and 5c show, respectively, the voltage and current across the varistor in the suppressor. Note that the maximum voltage is 600 V for a 550 A 

current on the varistor. (The current in the suppressor is lower than the ava

able short-circuit current as a result of the reduced driving voltage, becau

the varistor holds off 600 V. 

Fig. 6 shows several osc~llograms indicating how the surge propagates 

the wiring in the absence of any wppressor. Fig. 6a shows the open-circu

voltage at the service box. At the open-ended 7.5 m (25 ft) line, the voltage 

substantially the same as at the box (Fig. 6b). However, at the end of the 30 

(100 ft) line with a 50 Q termination, a significant decrease of the slope is n

ticeable, while the crest remains practically unchanged (Fig. 6c). 

(a) open-circuir volrage-ai box 

(b) open-clrcult vollage-7.5m (25 ill (cl open-clrcuil voltage - 30m (IW fl) 

Fig. 6. Propagation of surge. 

With voltage limitmg at the box provided by the installation of a suppre

sor, even at a remote outlet, an arrester connected at the service box would n

reach its sparkover voltage until rubstantial surge currents were involved. 

larger current was requ~red for a short distance between the service box an

the suppressor than for a greater distance. The value of the current requir

to reach sparkover as a funaion of the distance is therefore of interest. 

For a distance of 7.5 m (25 ft) the threshold condition for sparkover of t

arrester is shown in Fig. 7. In Figs. 7a and 7b the open-circuit voltage an

short-circuit current are shown for this threshold setting of the generator. I

spection of the oscillograms shows an open-circuit voltage of 8.1 kV, with 

calculated equivalent source impedance of 4.2 R. This low value of the sour
impedance, compared to proposed values 151, provides a conservative evaluation of the system performance. For the same setting as Figs. 7a and 7b, the 

oscillograms of Figs. 7c and 7d show the case in which the arrester has sparked 

over, as indicated by its voltage (7c) and current (7d) traces. In Figs. 7e and 7f, 

the traces show the voltage (7e) and current (70 in the suppressor for a case in 

which the arrester did not spark over (as a result of the scatter of sparkover or 

a slight difference in the output of the surge generator). This case represents 

the most severe duty to which the suppressor would be exposed, for a distance 

of 7.5 m (25 ft) 

(a) opncircult voltagc (b) short-circuit current 

(c) voltageat arrester when arrester dm sparkover - suppressor at 7.5 rn (25 It) 

Id) rurrcnl marrcsIcr allcr ,prrk~,rr - 

wpprrsrur at 7 I m (25 It) 

(e) voltageal suppressor when arrestor does not sparkover - suppressor at 7.5 rn (25 It) 

(0 current in suppressor when arrester docs not sparkover - suppressorat 7.5 m (25 ft) 

Fig. 7. Transfer of surge conduction 

From these tests it is apparent that the I200 A flowing in the line to the 

suppressor (70 and establishing 1000 V at the varistor terminals (7e) causes an 

additional 1OOO V drop in the line. The resulting 2000 V appearing at the arrester terminals may cause sparkover of the arrester (7c). 

For a case in which there is no arrester installed at the box but only the 

suppressor installed at an outlet, the voltage rise in the wiring and the meter 

coils will most likely result in a flashover of the system, which would then divert the excessive energy away from the suppressor, just as the arrester did in 

the test. Of course, this diversion may be destructive, a result that the arrester, 

when ~nstalled, is prec~sely designed to prevent. 

For greater distances between the suppressor and the arrester, the transfer 

of the surge wtll occur at lower currents. For instance, w~th the suppressor 

installed at the end of the 30 m (100 ft) line, only 700 A were required in the 

suppressor to reach sparkover of the arrester. 

Discussion 

The tests on simulated high-energy surges indicate that a transfer occurs 

from the suppressor to the arrester at a current level which depends on the distance between the two devices. Even for a short length of wire, the suppressor 

is relieved from the surge by sparkover of the arrester before excessive energy 

can be deposited in the varistor of the suppressor. At lower current levels, 

where the voltage in the system is clamped by the suppressor and thus prevents 

sparkover of the arrester, the suppressor absorbs all of the surge energy. 

In all instances, the voltage level at the suppressor is held low enough to 

protect all electronic appliances having a reasonable tolerance level (MX) V in 

most cases, IOOO V in some cases). Furthermore, the installation of only one 

suppressor in the house provides substantial protection for other outlets, 

although optimum protection requires the use of a suppressor at the most sensitive appliance, with additional suppressors for other sensitive appliances. 

V. SURGE INJECTED INTO GROUND SYSTEM 

Assumptions 

For this experimenl it was postulated that a lightning stroke attaching ta 

the primary side of an overhead distribution system would produce a branching of the current flow into the ground after sparkover of the pole-mounted 

utility's surge arrester (which was presumed connected at the pole-mounted 

distribution transformer). Fig. 8 shows the assumed circuit and the division 

of current flow. 

'k,- " :"'" 

Fig. 8. Division of current assumed for a 100 kA stroke. 

In their study of lightning environments, Cianos and Pierce [61 indi

that only 5% of all ground strokes exceed a peak current of 100 kA. The 

quency of the strokes is dependent upon the geographic location (isokerau

levels) (71, as well as upon local configurations. The probable mcurre

of a stroke involving the utility pole near a house with no adjacent tall tree

buildings is I per 400 years for most of the U.S. For a 5% probabi

the likelihood can be reduced 20 times; in areas of high lightning activity, 

likelihood can be reduced 10 times. A stroke exceeding 100 kA at one l

tion, therefore, can be expected to occur only once in 10,000 years (but t

are millions of poles in the U.S.). 

From these assessments, the maximum current to be injected for the ho

model under discussion was selected to be 30 kA. From this maximum 

30 kA injected into the ground wire of the houseservice drop, two more va

were used during the test series: 10 kA, corresponding to the requirement 

the ANSl high-current, shortduration test; and 1.5 kA, corresponding to 

requirement for the ANSl duty-cycle rest -both specified by ANSl Stan

C 62.1 for secondary valve arresters (31. All had wavethapes of 8 x 20 ps. 

Another reason for selecting this low level (1.5 kA) was that no spark

occurs in the wiring at this level. For the 10 and 30 kA levels, multiple fl

overs occur at variable times and locations, making exact duplication of 

impossible. By limiting current to below sparkover levels, repeatability of 

results was ensured, allowing comparisons among several alternate cir

configurations. 

The generation of transient voltages in the house is attributed to elec

magnetic coupling. The lightning current in the messenger establishes a 

that couples into the loop formed by the two phase wires encircling the m

senger. In addition, there is some capacitive coupling between the w

(Fig. 9). 

Fig. 9. voltages induced in the house wiring system. 

Test Circuit 

The test circuit consisted of a high-current impulse generator, a distr

tion transformer with a service drop, a simulated simplified house wiring 

tem, and the necessary shielded instrumentation. 

The service drop connection between the distribution transformer and 

meter socket was made with three 13 in: (45 ft-) long AWC #6 wires, twi

at a pitch of about 5 turns/m (1.5 turns/ft). This service drop was folded 

loose '5" shape at about 0.5 m (1.5 ft) above the ground plane serving as 

return path for the lightning current, in order to reduce the loop inducta

seen by the generator. This configuration does not influence the coupling 

tween the messenger and the wires wrapped around it, coupling which has b

identified as the voltage-inducing mechanism. 
The simulated house wiring started at the meter socket and continued to a 

load center over a distance of 3 rn (10 ft). From this load center four "branch 

circuits" connected to the load center breakers were established, each terminating at a wall receptacle. Individual lengths of the branch circults were 6, 

12.24. and 48 m (20.40. 80, and 160 ft). 

Test Results 

Many tests were performed to investigate the effects of various combinations. A selection was made from ceveral hundred recorded oscillograms to illustrate these effects. The results are presented in the form of oscillograms 

with corresponding commentary, generally providing a comparison of voltages 

and currents with or without protectors installed. 

The first striking result noted was that the injection of a unidirectional impulse into the ground system produces oscillatory voltages between the phase 

and ground wires. Inspection of the no-load oscillogram (Fig. IOa) reveals 

two interesting phenomena. First, the frequency of the major voltage oscillation is constant for all branch circuit lengths (period = 2 ps). Thus, we can 

conclude that this frequency is not affected by the line length and that other 

circuit parameters, rather, are responsible for inducing this 500 kHz oscillation 

from a 8 x 20 ps current wave. Second, the minor oscillations v~sible during 

the first loop in each oscillogram are spaced apart at a distance that increases 

with line length. One can conjecture that these may be caused by reflections. 

Loading the line termination with a 130 Q resistor (Fig. lob) eliminates the 

later oscillations and reduces the first peak to about 60% of the value without 

load. From this reduction. a Thevenin's calculation of circuit oarameters. if 

applicable in an oversimplified form, would show that 130 51 is 60% of the 

total loop impedance, while the source impedance* is 40% of the total loop 

impedance. Hence. one can conclude that the equivalent source impedance 1s 

in the order of four-sixthsof 130, or about 85 R, in this scenario. 

Fig. 12 shows the recordings made during a 30 kA current injection. This 

extreme condition is capable of producing a 3500 A current In an arrester installed at the service entrance (Fig. 12a). If now we postulate a pessimistic 

situation where there is no arrester at the service entrance, but only a suppressor at an outlet, there are two possible outcomes. When no wiring sparkover 

occurs, as discussed in Section Ill, all the surge is indeed forced upon the suppressor (Fig. 12b). This current may be excessive for some suppressors, but 

this example is certainly a limited case. The more likely scenario is illustrated 

in Fig. 12c, where sparkover of the wiring upstream of the suppressor limits 

the current in the suppressor. In this last scenario, protection is obtained 

downstream from the suppressor. It is important to note that no additional 

hazard is created by installing the suppressor: the undesirable sparkover 

would occur even without the suppressor; in fact, without the suppressor, 

sparkover would be even more likely to occur. 

VOLTAGE WITH 1300 

COhNFCTFn ATOUTI FT 

INDICATED 

Sweep lpr dn 

h, VO tascat outkt 

mdrated SW V dn 

Fig. 10. Open-circuit voltages and effect of terminal impedance. 

Injected current: 1.5 kA. 

With no protectors at the load center nor at any outletc, the wiring flashes 

over at I0 kA injected current, but not before crests in the range of 8 kV have 

been reached (Fig. I la). With an arrester installed at the load center, voltages 

are limited to 2.2 kV, with about I kA current discharge in the arrester 

(Fig. Ilb). While eliminating the hazard of a wiring flashover or the failure 

of a typical electromechanical device, this 2.2 kV protective level may still be 

excessive for sensitive electronics. 

VOLTAGE AND CURRENT WITH 

ARRESTER ON LOAD 

CENTER 

Sweep: 2 rddiv 

Current In arrescer 

400 A/dw 

Voltage Across Bur 

5W V/d~v 

(c) Wiring Flashover 

Fig. 12. Duty imposed on stngle suppressor with 30 kA injection 

VI. CONCLUSIONS 

Coordination of surge protectors is feasible with existing devices, even if 

device characteristics vary. The experiments reported in the paper show three 

facts from which conclusions can be drawn: 

Fact I. Where a unidirectional current is injected into the ground system 

only, the responseof the system is an oscillaringvoltage, at 500 kHz 

for the system described. 

Fact 2. The equivalent source impedance, as determined by loading the 

system, is in the range of 50 to 100 R for the particular system 

investigated. 

Fact 3. Without substantial connected loads in the system, the open-circuit 

surges appearing at the service entrance propagate along the branch 

circuits with very little attenuation. 

Concl. 4. Coordination of surge suppressors requires a finite impedance to 

seoarate the two devices. enabline the lower voltaee device to oerConcl. 5. 

Concl. 6. 

fokm its voltaee-clamoine func~i~n while the hieher voltage debice . - performs the energydiverting function. 

The concept that surge voltages decrease from the service entrance 

to the outlets is misleadmg for a lightly loaded system. Rather, the 

protection scheme must be based on the propagation of unattenuated voltages. 

Indiscriminate application of surge protector? may, at best, fail to 

provide the intended protection and, at worst, cause disrupt~v

operation of the suppressors. What is needed ir a coordinated approach based on the recognition of the e%ential factors governing 

devices and surge propagation. 

Fig. 11. Protection provided by arrester at service entrance. VII. ACKNOWLEDGMENT 

Injected current: I0 kA. 

The contribution of K. E. Crouch in obtaining the current injeclion lest 

'Not to be confused with the surge impedance (L/C)'/' of the line. results i5 gratefully acknowledged.