The effect of repetitive surges on transient 

overcurrent and overvoltage protective devices 

François D. Martzloff 

General Electric Company 

Schenectady NY 

Reprinted, with permission, from Proceedings, EMC Zurich Symposium, 1985 

Significance 

Part 7 – Mitigation Techniques 

This paper is a condensed version, presented to an international audience, of the IEEE IAS 

Transactions, “Matching surge-protective devices to their environment” which is reproduced in 

Part 7 of the Anthology under the hyperllink “Matching environment”. 
THE EFFECT OF REPETITIVE SURGES ON TRANSIENT OVERCURRENT 

AND OVERVOLTAGE PROTECTIVE DEVICES 

Franqois D. Martzloff 

Corporate Research and Development 

General Electric Company 

Schenectady, NY 12345 

INTRODUCTION 

The occurrence of transient overvoltages in low-voltage 

power circuits has been recognized, and new standards have 

been published in recent years [l-41 that provide quantitative information on the voltage levels to be expected. Concurrently, the technology of metal oxide varistors has 

gained wide acceptance in the suppression of these transients [5-71. These varistors provide an effective method of 

diverting surges away from sensitive loads by offering a 

low-impedance path to the flow of current, maintaining a 

quasi-constant voltage across their terminals. This surge 

current diverted in the varistor produces within the bulk of 

the varistor material the deposition of energy, with the 

long-range effect of a progressive shift in the varistor 

characteristic. This phenomenon has been well documented 

[8,91, and the proper application of varistors can deal with 

the effect without adverse consequences. 

Manufacturers of metal oxide varistors publish ratings 

which include a family of curves, generally described as 

"Pulse Lifetime," that show the number of surges which a 

given varistor can absorb before some arbitrary limit of 

characteristic shift is reached. These curves show numbers 

of surges of equal amplitudes for a set of waveshapes; the 

actual occurrence of surges, however, is a full range of 

values, from the lowest to the highest, and also of different 

waveshapes. 

Attempts to simplify the description of surge 

occurrences have resulted in the statistical information of 

lEEE Std 587-1980, where a family of curves has been 

obtained from actual surge recordings; these curves show 

the frequency of occurrence of surges as a function of the 

voltage surge level, for various exposures' (Figure 1). 

Carroll fitst developed a method [lo] whereby the statistical 

information of IEEE 587 can be combined to predict the 

effect of the range of surges, as opposed to constant amplitude surges, on the varistor Pulse Lifetime. Korn has 

shown [Ill how a simple set of assumptions and computations based on Figure 1 and Pulse Lifetime curves can provide an estimate of the time required to reach the varistor 

rated Pulse Lifetime. 

This paper provides further guidance in applying this 

method, including the selection of environmental characteristics in the context of IEEE 587. Since the statistical 

nature of surges must be recognized, provision must be 

made for the rare cases where a properly applied varistor 

might still receive excessive energy, and age or fail prematurely. The common practice in dealing with this eventuality is to add a fuse in series with the varistor in order to 

eliminate the fault current that might flow in the failed 

varistor. Thus, the fuse will be subjected to the surges 

absorbed by the varistor, and should not blow under a single surge, nor should it be affected by the accumulation of 

surge currents at amplitudes slightly below the melting 

SURGE CREST LV 

*In some locatvxq rpvkover of clearances may llmlt 

the overvoltages 

Figure 1. Rate of surges occurrence vs. voltage le

(from IEEE Std 587-1980) 

level. Unfortunately, published time-current character

of fuses do not provide information on their performan

the short times and high peak currents involved i

operation of a surge diverter. To fill this void, a ser

tests was performed on various types of fuses; the 

results are presented in the second part of this paper. 

MATCHING THE VARISTOR CAPABILlTY 

TO THE ENVIRONMENT 

Two examples of environments will be used to ev

the effect on typical varistors that might be selecte

transient protection. In the first example, the poi

application is the service entrance to a building; i

sgcond, we postulate a varistor installed in an app

located somewhere in the building, with no protection 

vided at the service entrance. These two example

illustrate the approach, so that other types of applic

can be evaluated in a similar manner. 

A table can be developed based on the informati

Figure 1 and combined with the Pulse Lifetime data 

lished by the manufacturers, to estimate the time req

for a given varistor size to reach its rated life in a 

environment. One should recognize that these calcul

are based on graphical data which do not allow three

accuracy, even if the numbers shown on the table ar

ried to three digits for the sake of checking the arith

Furthermore, reaching the "rated life" does not mea

the device has reached the end of its service life. The 

lished Pulse Lifetime ratings are based on the arb

definition of "rated life" as the point at which the no

voltage of the varistor has decreased by 10%. This c

of voltage is indeed indicative of some physical chan
the varistor structure, but it does not affect the ability of 

the varistor to clamp surges in the high-current region. For 

properly applied varistors, a change of 20% in the nominal 

voltage would not be objectionable, so that this "rated life" 

is a very conservative limit. 

The first task of this development is to convert the voltage surge density probability of IEEE 587 (Figure 1) into a 

histogram of surge occurrences at the different levels of 

voltage. From Figure 1, selecting a given exposure, one 

can obtain the level of voltage surges occurring at different 

frequencies, or the number of occurrences between two 

voltage levels defining a cell of the histogram. 

Referring to Figure 2, the Medium Exposure line of 

Figure 1 has been redrawn, and voltage cells of approximate equal width (on the logarithmic scale) have been 

drawn, with the center values as shown in the figure, on 

the left side : 13000, 10000, 8000, etc. From the Medium 

Exposure line, the corresponding frequencies of occurrence 

are read, as shown in the first column of numbers to the 

right side : 0.03, 0.07, 0.18, etc. These numbers are the 

number of occurrences exceeding the level, so that the 

number in the the cell itself is the number for the level, 

minus the number for the level to the right. For instance, 

the number of occurrences in the cell of level 10 000 V is 

0.07 - 0.03 = 0.04 occurrences, and so forth for the other 

cells. 

Surge recordings, such as reported in IEEE 587, have 

shown that switching transients are not likely to exceed 

3000 V; therefore, we can attribute all the occurrences 

above 3000 V to lightning, and assume an 8/20 ps 

waveform for the resulting current in a varistor connected 

at the first interface. Conversely, the occurrences below 

3000 V can be considered as an undefined combination of 

switching transients and lightning transients. It seems reasonable and conservative to consider that half of these may 

be lightning, with the corresponding high energy of the 

8/20 ps wave shape, while the other half may be switching 

surges with the corresponding 0.5 ps - 100 kHz which has 

negligible energy content, compared with the 8/20 ps. 

Therefore, the numbers for the cells below 3000 V shown 

in the last column of Figure 2 are one half of the number 

of occurrences computed for each cell. 

The first example of application will be a 32 mm varistor, rated 250 V, which is assumed to be connected at the 

entrance of a building, and thus would be subjected to the 

Category B (IEEE 587) surges. As shown in Figure 3, 

these surges are defined as 6 kV open-circuit voltage and 

3 kA short-circuit current. The ratio of voltage and current 

can be considered as the source impedance of the surge, 

2 in this example. 

Referring to Table 1, the first column shows the voltage 

level of each cell; the number of occurrences for that level, 

as derived in Figure 2, is shown in the second column. 

From the varistor V-I characteristic (Figure 4), an expected 

Voltage Level of Cell Number Due to Llghtn~ng 

loo~~i~xj~~lng Level Number 11 Cd; 1 

1 780 390 

500 

1700 

Medium 

2400 

0.01 500 - 1000 2000 5000 10.000 20,000 

volts 

Figure 2. Derivation of the cell histogram 

clamping voltage can be derived by iteration for the rang

of resulting current expected at that voltage level, as show

in the third column. The voltage of the cell, minus th

expected clamping voltage, is the driving voltage shown i

the fourth column. With the 2 R source impedance derive

above, this driving voltage, divided by 2, yields the result

ing current shown in the fifth column. Turning to th

Pulse Lifetime curves of Figure 5, the rated number o

pulses for each current level are shown on the sixt

column. Finally, the last column shows the percentage o

rating consumed for the number of pulses at any level; fo

instance, at the 3200 V level. with 4 occurrences at 

current of 1220 A, hence a rating of 500 pulses, me per

centage consumed is 4 : 500 = 0.80%. The sum of th

percentages of all levels, then, is the percentage of ratin

consumed in one year, which yields the number of year

required to reach the rated value, as shown at the bottom

Surge Voltages and Currents Deemed to Represent the Indoor Environment 

and Recommended for Use in Designing Protective Systems 

Energy Uoules) 

Imphe Type Deposited in a Suppressor* 

Comparable to of Specimen with Clamping Voltale of 

Location 1EC No 664 Medium Exposure or had 500V 1 OOOV 

Categor~ Category Waveform Amplitude Circuit (120 V System) (240 V System) 

A Long branch 

Clmuits and 11 6 kV 0.5 11s-100 kHz 200 A Hi& impedance? - outlets Low impedance?. 5 0.8 

B Major feedern. 1.2 X 50ga 6 kV High impedenee? - - short braneh I11 8 X 20gs 3 kA Low impedance* 40 

- 80 

cireuitr.and 0.5 w-100 kHz 6 kV High impedance? - 

load center 500 A Low impednnceT.5 2 4 

'Other ruppresrolr having different elamping voitaecs would receive different energy levels. 

?PO* high-impedance test specimens or load circuits, the voltage shown represents the surze voltage. In making simulation tests. use 

that "due for the opencircuit voltage of the test generator. or IowimPcdance test specimens or load circuit% the current shown represents the discharge current of the surge (not the shortcircuit carrent of the power system). In malune simulation teats use that current for the ahorti.ircuit e-ent of the test genexator. 

P~he mnxlmum UnPlrtude (200 or 500 A) is specified. but th; exact waveform will be influenced by the load ehnrsetaristien. 

Figure 3. Voltages and currents in IEEE 587, Categories A and B 
Table 1 

Time to Reach Rating for a 32 mm, 250 V Varistor 

in Medium Exposure, Category B Location 

Voltage Number Expected Available Resulting Rated Percent 

level of 8/20 clamping driving current number of ratlng 

of cells occurrences voltage voltage at 2 fl of pulses consumed 

1000 12 000 6000 8 

920 9080 4540 15 

840 7160 3580 25 

810 5 190 2595 60 

780 3720 1860 200 

760 2440 1220 500 

740 1660 830 1500 

720 980 490 4000 

700 500 250 20000 

680 120 60 1 o6 

Total Percent of Rating Consumed in One Year 

Years Required to Consume 100% of Rating 

Figure 4. V-I characteristics for 14, 20, 

IYWLM DURATION - u IMPULSE DURATION - + 

Mm 

5003 

LWO 

3003 

: 2003 

d rm 

8 'Z 

? so0 3 - 

NOTE: End of Itfellme 15 defmed as a degradarlon fmlure whxch 

occurs when the dev~cc exh~btts alhift ~n the vanstor voltage at 

one( I) rnilltarnpereexceed~ng + 10%. + IV of the lnltlal value 

This lype of tallure 1s normally a result ofa dccreaslng V value. 

hut does not prevent the dev~ce from conl>nu~ng lo functnon 

However. the varlslor wtll no longer meel the orlgmal spectf~ca 

I,""< 

300 

1 W 

Figure 5. Pulse lifetime ratings for 14, 20, and 32 mm varistors rated 250 V RMS 

5 5 51~ 510' 51~ 510. 51~ 

PEAK AUPERES 

and 32 rnm varistors rated 250 V RMS 

- VlYlUElYl 

Vt30HE15C 

I 
For the selected example of a 32 mm varistor, rated 

250 V and connected in a Category B location at Medium 

Exposure, it would take 23 years to reach the rated pulse 

life of the device under the conservative assumptions made 

in this example. Once again, reaching "rated life" does not 

mean reaching a device failure level. 

Another example of estimation will be useful to illustrate the process and the type of reasonable assumptions 

that can be made. Consider a varistor installed on an appliance connected at some point distant from the service 

entrance, still in Category B, Medium Exposure. Table 2 

shows the corresponding pairs of numbers of occurrences 

and levels, from which the same computations can be 

derived as before. We will add some impedance to the 2 

value used in the preceding example, say 2 0 for an 

8/20 ps surge propagating in a few meters of wiring [121. 

For this example, we will compare a 20 mm varistor to a 

14 mm varistor, both rated 250 V; the same value of 

expected clamping voltage will be used for both devices 

(Figure 4), and the resulting surge current will be computed, as shown in the fifth column of Table 2. Referring 

to the respective Pulse Lifetime rating curves for the 20 

and 14 mm devices (Figure 51, we obtain the number of 

pulses allowed to reach the rating, shown in the ne5t two 

columns, and compute the yearly consumption for each 

device at each level. Again, the total is shown, with the 

resulting number of years required to reach the rating: 

20 years for the 14 mm device, and 50 years for the 20 mm 

device, in the environment of this example. 

Thus, we have a method for estimating the effect of the 

environment, as defined in lEEE 587, on the ability of the 

varistor to function reliably in that environment. Indeed, 

the evaluation is only as good as the assumption made on 

the actual environment, compared to the generalized 

description given in IEEE 587; nevertheless, it represents a 

reasonable and reasonably conservative approach to selecting device ratings for reliable operation and make comparisons between different device sizes. Carroll has shown, by 

computer-aided analysis [141, that the estimation tends to 

yield increased years as the width of cells is made smaller, 

reaching an asymptote over one hundred cells. In the 

examples shown here with fewer cells, aimed at a rapid estimation, the log-log coordinates tend to weigh the results 

toward a pessimistic estimate when the cell numerical 

center is taken at the geometric center. 

FUSING OPTIONS 

It is well recognized that extreme values can be found 

which will exceed the predictions of limited-base statistics, 

so that one must always take into consideration the case 

where excess energy might be deposited in the varistor. 

Like any other electronic component abused in this 

manner, it will fail, generally in a short-circuit mode. 

Table 2 

Depending on the available short-circuit current at t

point of the system, the current flowing in the failed va

tor can produce melting of soldered connections or shat

ing of the device. Since these ultimate failure modes 

not generally desirable, common practice would be to p

vide an overcurrent protection in series with the varistor

order to clear the fault from the circuit. 

Two approaches to fusing a varistor can be consider

as shown in Figure 6. In Figure 6a, providing the fuse 

series with the load ensures that in case of varistor failu

the power is removed from the load, so that it will not 

exposed unprotected from further surges. In Figure 6b, 

varistor fuse inserted in shunt with the varistor ensures 

the power supply to the load will not be interrupted b

spurious varistor failure, but only at the price of leaving 

load unprotected against further surges. As pointed ou

industry standards [91, each of these scenarios may be 

preferred one to some users, so that the "fail safe" desc

tion would be misleading to the opposite view. 

instance, an application can dictate that maximum ser

continuity be ensured, so that Figure 6b would be lab

"fail safe" by those requiring this mode of failure. O

users, anxious to protect their hardware even at the pric

losing the function, would label Figure 6a as "fail safe." 

For the Figure 6b configuration, the only requirem

for the fuse is to ensure fast removal of a failed vari

and yet not blow under the surges presumed to flow f

time to time in the varistor. Hence, the selection of 

fuse should reflect the expected surge currents. Un

tunately, data currently made available by fuse manufac

ers do not extend the i2t ratings into the microsec

a) Protectton mainta~ned, function interrupted - 

b) Functlon mamtalned, protection lost 

Figure 6. Fusing options for varistors 

Time to Reach Rating for 20 and 14 mm, 250 V Varistors 

in Medium Exposure, Category B Location 

Voltage Number Expected Available Resulting 

of 8/20 level clamping driving current 

occurrences of cell voltage voltage at 4 

8 000 0.18' 800 7 200 1 800 

6 000 0.32 760 5 240 1310 

4 500 1 730 3 770 942 

3 200 4 710 2 490 622 

2 400 6 700 1700 425 

1700 22 690 1010 252 

1200 80 680 520 130 

800 390 670 130 32 

14 mm 20 mm 

Rated Percent Rated Percent 

number of rating number of rating 

of pulses consumed of pulses consumed 

12 1.5 80 0.20 

40 0.80 110 0.30 

100 1 200 0.50 

600 0.67 1000 0.40 

1100 0.55 2 000 0.30 

6 000 0 37 10 000 0.22 

50 000 0.16 90 000 0.09 

2.10~ 0.02 > lo7 - 

Total Percent of Rating Consumed in One Year 5.07% 2.01% 

Years Reauired to Consume 1009/0 of Rating 20 SO 

' Surges above BOO0 V are not likely to propagate in low-voltage wiring w~thout causing operation of a 

protective device, or flashover of a clearance upstream [131, so that the varistor installed downstream in 

the Category B location will not be subjected to the energy associated with levels above 8000 V. 
range, nor do they provide guidance on my necessary 

derating of the fuse in order to account for the poss~ble 

effect of repetitive surges at levels slightly below the nielting level. The second part of this paper therefore :lints at 

providing some information on this selection process. This 

information is based on a limited test program conducted 

on various types of low-voltage fuses that might be considered for fusing a shunt-connected varistor 

It should be noted, of course, that while the operatior: 

of the fuse in the series connection (Figure 6b) has generally an obvious effect on the system operation - ahut 

down - operation of the fuse in the shunt brdnch is ri:it 

immediately apparent. Depending upon the applica~ion anc! 

the economics of the situation. ~t may be desirable Ic pr(w 

vide some indication that the varistor is np longer protect. 

ing the circuitry. 

An experimental program was ctindurt~~,i on viir:o~is 

fuses in order to determine the rnininiurr :lmpere rating 

required for the fuw not to biow under :ht: iurr cuyrer:i 

that may be diverted by he varistor ar its expt.;:ed poi,-!! nt 

installation. Th~s niminiuni !imir not ~~nly in\-olxcs :I c>lrren: 

level for one single surge, hut also a currcni ievel, presilr, 

ably lower. for many puise~. Tlli; rl:~:iIrty is p21~lici to +b,. 

situation discussed :or the ~,iii,i.?!s, ~h-rs tltc Pulse L:te 

time is a function of three p.irami:ei\ currcr i *-aeak 

current duration. and nurnbc: or palwi Vnfoctu?:;,. i: 

fuse manufacturers have no' o: ,':I\ ,ii1, ,~"trli*;irci .,I > 

mformation on microsecond-iut~g ,arrrv! pu14e'i, lit 1h.1: 

users resort to empirical der.~ting ;.IL;~~S:. I;, atlrii,pn.i. 'iseffect, resembling fatrgde. of mu:tip.i- :;ilizc\ 

Results of tests made on two i~pes of ~:urrei~t-!im~t~ilg 

fuses are presented here tu illustrate the e'ects of repet!. 

tive surges and to motixatr .i discbsswi! o! ts.c iv.~;.'.: 2nd 3 

sharing of information. 

The fuses weic both reied l'ilr 2511 \ circugi voliagi:. 

with an interruptrng c;ip,rcity of It) k J. !ci.re<en:n!i, .- ,'f 

what might be used in an epplicat~:)rr w!ri: moderate 'nnii 

currents. The construction I,! fuse5 rated for higher ;pir,, 

pective fault currents, such .%i 100 kA. 13 dirf's:er?t primaii!: 

in the current-limiting chaacterisrics: ive xc c:ln 

cerned with the elernenl-melting ch,iraircr~stts~ 4 n1oi.t: 

comprehensive program will ha\< ill eitend the invesrig: 

tion to the behavior of fuses with high lntzrrupting cap*:.- 

ity, as well as circuit voltapes ui~ lo 600 \ 0r1~ fuse w.4~ 

the so-called "fast fuse." with a ratici of 13.1 between ;!.ie 

melting currents at 1000 and a1 3.01 s ihe orher fuse 

type, the so-called "rime delay." had d rntio pi 37:l Burti 

were rated 3 A: Figure 7a shows an X-ray photograph i!f 

the 3 A fast fuse and Figure 7b si:ow the 3 4 timi: delay 

fuse. 

The current waveform se!ecied f,:r tbz rest wa.; [tie standard 8/20 FS impulse used for characterizing varistors and 

other surge protective devices. Figr;rc a shows such an 

impulse, for whickt the I)! intefrai car, be cvmputed. For an 

impulse of 1000 A crest, the 1'1 value of an 8/20 ps 

impulse is 19.5 A 's. 

Fast Fuse Tests 

The 3 A fast fuse used in the test has a melting current 

of 46 A rms at 0.01 s, which corresponds to an 1'1 c;f 

21 A2s. By subjecting each of 10 fuses to a single-shot 

impulse in the range of 1100 to 1000 A crest, the nominal 

melting current crest of 1050 A, 8/20 rs, was established. 

This current impulse has an r2i content of 21.5 A'S, which 

shows a remarkable correspondence to the i2t a1 0.01 s with 

sine wave current. We will designate this single-impulse 

melting i2r as 12T. 

RCnet~ti\c irvpuise-., :! 3 rr~W sufliclently low to avoid 

:!ccurntii,i~ion r)! h-s; '17 :he fuse. were applied to several 

g?i~t.:ir of Fuiss Thc his1 group was subjected to impulses 

:;! 9OC!1 rbf rh. melt!. g .:urrent. :he second at 60°/i:. and the 

.bird d: 30''. ... corre\pondinr respectively to i't contents of 

81. 36. 'ind Y% if the melting :'T In the 8IUh i2r group 

i~f I0 fuses. .ill eventudly imelteti as the repetitive impulses 

wcrf applied. The first wen1 ;it :he third shot, the last at the 

ixivttiirti shot. In ths 36"h I- r group of 10 fuses, four 

lusei melted a1 ',hot niambers ranging From 5 to 208. No 

rr~i-!h~r impllses wre dpplied past 200 shots Each of the 

wri,iving ruses was '!?.en hubjected to a single impulse of 

higher value 10 determine the one-shot nielling current in 

this "aged" iondition That vnlue was fourid to be 1050 A 

Lrest. unchai~ged from the new conditrun. The 9% I'T 

gro1.p. cunt;iining 20 !'use.; received 800 impulses; none 

meited. Ten of lhese were subjected to a s~ngle impulse at 

1050 .4 ( 100°~! 1'7). 6 +wt :he li) melted at that current, 

the four others survived. 

From rhcse results, 11 seems that a reasonably safe i'i to 

en>?sre no nrlting of the fuse when exposed to repetitive 

current in?pulses is in the order of 2S?h of the single 

impulse melting 1'7' The value of 12T to be used for taking the 25'41 limit can be obtained from the published melting current at 0.01 s However, even at 10% of the single 

impulse melting i'T. a slight aging of the fuse is detectable, leadrng to a decreased current capacity. At 36% i2T, 

some early mortality is observed, but the survivors do not 

appear to have aged more than the 10% 12T group 

'1 ime Delay Fuse Te5ts 

As an alternative to substantial derating of a "fast" 

fuse, the so-called "Lime delay" offers the possibtlity of 

being able to survive larger impulse currents. The larger 

ratio of 37:l between 1000 and 0.01 s currents allows 
maintenance of a comparable overcurrent protecti capability in the medium range, where a varistor failur might 

require the fuse to melt in relatively short time. 

The 3 A fuse tested in this program has a 0.01 s -nelting 

current of 130 A rms, or an i2t of 169 A~S. By the same 

bracketing procedure applied to the fast fuse, the 12T under 

impulse of this fuse was determined to be 190 ~~t (somewhat higher than the i2t at 0.01 s), corresponding to a crest 

current of 3.2 kA at 8/20 ps. 

Preparing for repetitive impulses, it was found that at 

81% 12T, the fuses would not survive the second shot; at 

64% IZT, the fuses would melt at the second or third shot. 

The i2t had to be lowered to 50% 12T to allow passing 10 

shots. The 36% 12T group received 100 impulses without 

having one fuse melt; this is to be compared to 3 fuses out 

of 10 melted by the twentieth shot in the fast fuse series. 

These fuses conditioned by the 100 shots were then subjected to one single pulse each to determine the melting 

level, which was bracketed at 160 A2s, or a crest of 2.9 kA 

at 8/20 ps The third group of fuses in this series was 

exposed to 800 impulses at 9% 12T; no melting occurred in 

20 samples. Subjecting these successful survivors to one 

single impulse each bracketed the melting i2t at 90% of the 

un-aged I2 T (95% of the current), a small shift downward. 

These tests on the "time delay" type fuses also show 

some degradation or aging in the fuse, but somewhat 

different from the aging of the fast fuse type. The conclusion will still be that a derating on the order of 25 % of the 

12T (50% of the current) is required to provide reliable 

continuity of service under repetitive surge conditions. 

CONCLUSIONS 

1. Varistors can be selected to provide predictable performance under assumed surge conditions by combining 

the published Pulse Lifetime curves with environment 

characteristics. 

2. Guides on the surge environment in ac power circuits, 

such as IEEE 587-1980, can be used to generate a 

reasonable definition of the duty imposed on varistors. 

3. Current-limiting fuses that might be used in series with 

a varistor exhibit aging characteristics when subjected 

to repeated pulses, as they will in actual application. 

Pending availability of detailed information from 

manufacturers, a derating factor needs to be applied to 

the i2t ratings computed from the shortest time 

(0.01 S) of the time-current characteristics. 

Readers of this paper and users of fuses in impulse applications are invited to share information with the author in 

order to generate an irpproved evaluation of the problem. 

REFERENCES 

111 IEEE Std 587-1980, Guide for Surge Voltages 

Low- Voltage AC Power Circuits. 

[2] IEC Reports 664 and 664A-1980, Insulation Coord

nation Within Low- Voltage Systems, Including Clea

ances and Creepage Distances for Equipment. 

[31 R. Hasler and R. Lagadec, "Digital Measurements 

Fast Transients on Power Supply Lines," Proc. 3

Symposium and Technical Exhibition on Electroma

netic Compatibility, Rotterdam, 1979, pp. 445-448. 

[41 F.D. Martzloff, "Transient Overvoltage Protectio

The Implications of New Techniques," Proc. 4

Symposium and Technical Exhibition on Electroma

netic Compatibility, Zurich, 1981, pp. 505-510. 

[51 M. Matsuoka, T. Masoyama, and Y. Ida, "Suppl

mentary Journal," Japanese Sociefy of Applied Phys

39, 1970, pp. 94-101. 

[61 J.D. Harnden, F.D. Martzloff. W.G. Morris, a

F.B. Golden, "Metal-Oxide Varistor: A New Way 

Suppress Transients," Electronics, October 1972. 

171 H.R. Philipp and L.M. Levinson, "Zinc Oxide 

Transient Suppression," IEEE Trans. PH

December 1977. 

[81 Transient Voltage Suppression, Electronic D

Library, General Electric Company, Auburn, N

1982. 

[91 IEEE Std C62.33-1982, "Test Specifications 

Varistor Surge Protective Devices." 

[lo] E. Carroll, "Transient Attenuation with Metal Ox

Varistors for AC Mains Powered Equipment

COMEL Conference, Twente, Holland, 1980. 

[Ill S. Korn, "Transients and Transient Suppressors 

Power Conversion Equipment," INTELEC Conf

ence, Washington, D.C., 1982. 

[I21 F.D. Martzloff, "The Propagation and Attenuat

of Surge Voltages and Surge Currents 

Low-Voltage AC ,Circuits," Paper 82SM453-9, IE

Power Summer Meeting, 1982. 

[I31 F.D. Martzloff, "Coordination of Surge Protector

Low-Voltage AC Power Circuits," IEEE PAS-99 

Jan-Feb 1980, pp. 129-133. 

[I41 E. Carroll, private communication.