Reprinted with permission from Proceedings, 25th International Conference on Lightning Protection, Rhodes, 2000

Significance:

Part 2 – Development of Standards – Reality checks

Part 4 – Propagation and coupling of surges

Comparison between two simplified modeling studies of the dispersion and a documented case of the complexity of

a direct flash to a residence.

Reservations on the justification of very high stress requirements for SPDs are expressed in a discussion, followed

by a proposal to encourage more information sharing on the subject.

Filename: Dispersion
25th International Conference on Lightning Protection 5.1

18-22 September 2000 

ON THE DISPERSION OF LIGHTNING CURRENT 

AFTER A DIRECT FLASH TO A BUILDING 

Francois Martzloff 

f.martzloff@ieee.org 

National Institute of Standards and Technology* 

U.S.A. 

Abstract: Simplifications often made when simulating 

the dispersion of lightning current can yield results 

that depart too much from the complex reality of a 

direct lightning flash to a building. The unpredictable 

occurrence of side-flashes increases even more the 

complexity. Such simulations, if taken at face value, 

might lead to unrealistic specifications for serviceentrance surge-protective devices (SPDs). A real-world 

anecdote illustrates both the complexity and a case 

where an SPD with only modest ratings, compared 

wiih some present proposak, pyovided satisfactory 

protection on the power-port apphances of a residence. 

Key Words: Lightning current dispersion, sideflashes, surge-protective devices 

1. INTRODUCTION 

Recent discussions among participants in the 

development of surge-protection standards have shown a 

lack of consensus on-the~possiblescenarios concerningthe 

dispersion of the lightning current when a direct flash to a 

building is involved. Skepticism has been expressed both 

on the simulation of available paths for the dispersion, and 

on the magnitudes and waveforms postulated for the 

resulting currents flowing in the conductive elements of the 

installation - especially the service entrance surgeprotective devices (SPDs). Note that the skepticism does 

not aim at the parameters of the lightning flash itself, which 

have been accepted now for many years [I], but at the 

simulation conclusions concerning requirements for 

service-entrance SPDs with very high current-handling 

capability. 

Another objection has been that the distinction 

between a building equipped with a lightning protection 

system (air terminals, down-conductors and earthing 

system), on the one hand, and a building without such a 

system, on the other hand, might be misleading. 

Every building that contains electrical circuits (pow

or communications), electrically-conducting mechanic

elements, metallic structures, etc., has a de facto lightni

'protection' system of intended or unintended air termina

and down-conductors - except that their connection to t

earthing system might have unpredictable and unwante

side effects. 

As an input toward developing consensus, this pap

reviews in a first part two examples of simulations that ha

been performed by others, and in a second part relates 

real-world anecdote of a corroborated case of a direct fla

to a residence. 

2. SIMULATING DISPERSION 

2.1 Examples of simulations 

A Joint Working Group of the International Electr

technical Commission (IEC) has recently developed 

Technical Repad on surge pmntp,ctian[2]. This &-year 

effort involved the participation of five ZEC Technic

Committees interested in the subject. The data ba

considered by the group included, among many source

two published papers, identified in the Bibliography of t

report, authored independently by members of the group

In both studies, a 10f350 ps waveform was postulate

and a time-invariant earthing resistance and inductan

were postulated. Currents in the available paths to ear

and voltages at selected points of the systems we

computed. For the purpose of this paper, three figures on

are reproduced here for a qualitative glimpse on the resul

Figure 1, simplified from Ref [2], shows the nature 

circuit components and configuration: two buildings and t

distribution transformer linked by a cable in a line

arrangement. The point of strike is Building 1. The detail

numerical values, which are given in the referenced pap

are not significant for this comparison of the two studie

* Electricity Division, Electronics and Electrical Engineering Laboratory, Technology Administration, U.S. Department of Commerc

Contributionsfrom the National Institute of Standards and Technology are not subject to U.S. Copyright. 

ICLP zooo 41 
Figure 1 - Circuit components and configuration used in the Hasse simulation (Ref [Z]) 

Figure 2 shows examples of the computed waveforms 

for currents at selected points of the Figure 1 circuit, from 

top to bottom : the postulated stroke current, the current 

exiting Building 1 via the power supply cable, the current 

in the earthing impedance of the building, and the current 

in the service-entrance SPDs of Building 2 resulting from 

the surge that is now, for Building 2, an impinging surge. 

The radial service drops also consist of a resistance 

an inductance, not drawn in the figure, but modeled in 

computation according to the 20-m length of each ra

drop. The point of strike of the flash is the earthing sys

of Building 1 (to which the neutral is bonded). 

Figure 2 - Current dispersion for Figure 1 

The numerical values are not significant, but the 

waveforms are. The current exiting the building (IMa!,.,J 

has the same waveform as that of the stroke. The earthing 

current (Iearthing) has an initial peak, due to the additional 

inductance of the power supply cable; in the long term, the 

inductive effect disappears, and the current division simply 

reflects relative values of the available earthing resistances. 

In contrast with Figure 1 where the buildings are strung 

along a power supply cable, Figure 3, from Ref [3], shows 

a radial configuration of three buildings, each supplied by 

its own service drop, with all three connected directly to the 

terminals of the common distribution transformer. 

Varistor-type service-entrance SPDs are provided for each 

building. The transformer and each building have their 

own earthing electrode connection, represented by a fixed 

resistance and an inductance. 

Figure 3 - Buildings configuration and resultin

currents, according to Mansoor (Ref [3]) 

The significance of citing these two indepen

studies, separated by an ocean, by two different langua

used by the authors, and by two different simula

programs, is that quite compatible conclusions w

reached after exchanging information, first across the t

during IEC working group meetings, then later on, 

intensive e-mail messages, as a working relation

blossomed in spite of logistics barriers. This impor

point will be elaborated further in Section 7 of this pap
With hindsight, it appears predictable that the initial 

current dispersion (the first ten microseconds) should be 

strongly influenced by the relative values of the postulated 

inductances, and the later dispersion by the relative values 

of the postulated (time-invariant) earthing resistances. 

2.2 Involvement of service-entrance SPDs 

The results of these simulations show that the stresses 

imposed on the service-entrance SPDs that become 

involved in dispersing the part of the lightning current 

toward remote earthing electrodes of the power distribution 

system will reflect the relative values of the earthing 

impedances. These stresses also vary with the postulated 

current waveform, ranging from the short 8/20 ps long-used 

for designing SPDs, to the more recent proposed 101350 ps 

and finally to the seldom-considered continuing current 

within a multiple-stroke flash. 

Performing these simulations was not a futile exercise 

but provided insight on the influence of significant 

parameters. However, among end-users, this complexity 

of postulates decreases the credibility of defining SPD 

requirements on the basis of simulations, giving a greater 

credibility to field experience of widely-used SPDs that 

have demonstrated satisfactory performance over many 

years. 

3. SIDE FLASH 

One event that contributes to the complexity and 

uncertainty of lightning current dispersion is the possible 

occurrence of a side-flash. A side-flash can establish 

unexpected paths to earth, with two consequences that 

extend beyond the consideration of service-entrance SPD 

stresses - the motivating concern for this paper. 

The side-flash itself can have hazardous consequences 

by acting as an igniter, as will be told in the anecdote 

of Section 4. 

The side-flash can cause currents to flow along 

conductive paths within the installation, thereby 

coupling transient overvoltages in the circuits of the 

installation, by common path or by induction. 

Of course, the latter has the same end-result as what 

the bonding applied to avoid the side flash will produce, 

except for its unpredictability. 

4. FROM SIMULATIONS TO REALITY 

4.1 Setting the stage 

To illustrate the credibility gap that separates reality 

from simplified representations, the following story should 

be narrated: 

This engineer had bought a house from the previous 

owner who had lived many happy years there without any 

problem, so that our engineer made the (unwarranted

assumption that the house and its electrical wiring were in 

good order. The house was surrounded by several tall

mature trees so he thought that the cone of protection from 

the trees would benefit the house. Alas ! All-knowing Zeu

recognized that this engineer needed to be taught a lesson 

on reality and thus sent a downward stepped leader toward 

the general area of the engineer's house ... 

By now, dear readers, you have guessed that ou

mythical engineer is none but the author of this paper .

who will now offer this true story for your edificution

First, the "where" : Figure 4 shows a simplified (here w

go again ...) topology of the house, a two-story woodji-am

with basement and attic. Utilities (power, telephone, and 

cable TV), all entered, via overhead service drops, at th

rear of the house, while water and sewer underground 

pipes were at the front of the house. The telephone system 

was not involved in the incident and therefore is not show

in the figure. The power installation included the usua

revenue-meter (outside) and service panel (inside) wit

circuit breakers controlling a multitude of branch circuits

Only three are shown in the figure: lightingfixture in th

attic, TV on the secondfloor, and a counter-top receptacl

(via ground-fault interrupter) for the kettle (@in Figure 4

sitting on the enamelled cast-iron kitchen sink. (Th

significance of this detail will sulface shortly.) 

-Firm bonds - Dubious bonds 

.... Once upon a time, in a far-away land (Upstate New 

York, U.S.A.) there lived an engineer who was recording 

surges, writing papers and presenting tutorials on surge 

protection, including the need for good bonding practices. Figure 4 - Simplified configuration of anecdotal stor

ICLPLOOO 43
Water service and induorpiping were all copper, with 

a bond between the ground bus of the service panel and the 

nearest cold-water pipe. There was no visible grounding 

conductor to a (mn-existent) rnade-electrode, but the 

perception existed that, given the vintage of the house 

(circa l92O), the water piping was su.cient, in addition to 

the multiple-grounded neutral of the power company. 

Upon moving in the house, I had installed in the 

service panel a surge arrester (circa 1965 vzntagej 

consisting of a silicon-carbide disk in series with a 

stamped-metalair gap. The cable TV service, as origlnalJylnalJy 

installed by the utility, only had a 50-cm long picket 

allegedly serving as "ground". Having been exposed to 

the concept of bonding, I had installed a bond between the 

picket and the nearby outdoor waterfaucet. A very passive 

- bur soon to become active -part of the installation was 

the typical sewer system made of lead-bonded cast-iron 

pipe extending a to vent through the roof and connected to 

the street sewer, still with cast-iron pipes and thus offering 

the topology ofa well-grounded air terminal, albeit below 

the peak of the roo$ But I am getting ahead of myselj as 

I had never considered this vent as a lightning air terminal, 

since the house was surrounded by taller trees and thus 

"obviously" within their cone of protection. 

Now for the "When " and "How" : On the day when 

the tale unfolded, my wife (the corroborating eye-witness) 

and I were standing in the kitchen, listening to the 

approaching thunder and watching the big drops of rain 

just beginning to splash on the window. Then, a bright 

flash outside, with an immediate, deafening thunderclap, 

and also we both saw a small flash under the kettle. "That 

was a close one" we both said, whereupon Iproceeded to 

check all appliances in the house. Several were 

inoperative, but a check of their branch circuit breakers 

revealed that they had tripped, and resetting them restored 

order. The only one that did not work was the old TV set, 

although there was no evidence of severe damage or 

burned smell, and we considered ourselves lucky - until 

a smellfrom the attic attracted my attention: the ceiling of 

the attic (which was covered by cellulose-base panels) was 

smoldering ! 

Fortunately - and not by accident - a handy fire 

extinguisher allowed me to quench the smoldering, while 

my wife called the fire department. To their credit, they 

were infront of the house within minutes. I told them that 

I believed that the $re extinguisher had done the job; 

neverrheless, one fireman proceeded to climb on a ladder 

to the am'c window and hacked it away to let the smoke 

out, while another entered the house, pushing me aside. 

with a high power water hose in tow - which fortunately 

he did not turn on. Afrer ripping several of the ceiling 

panels to verify that the fire indeed was out, the firemen 

IeP, with our emotional- thanks and the applause of the 

neighbours gathered in front of the house. 

4.3 The homeowner's epilogue 

One obsolescent TV receiver, which was not repa

but catalysed the purchase of a new and upgrade

(missing the opportunity to do an extensive p

mortem as in the "Case of the Cozy Cabin" [4]). 

Several hundred dollars expended to repair the win

destroyed by the firemen, install a splice on one 

r&r weakened by charring, and- replacing the ri

panels. 

After raovering- fhmthe shock, a- realization of 

lucky to have been in tbe house at th~ time o

incident, and glad for the foresight of having a 

extinguisher on every floor of the house ! 

4.4 The engineer's epilogue 

Such a traumatic experience called for an investig

of the incident. The first observation was that the prev

owner had installed insulation between the attic raf

stapling the aluminum foil of the bats to the rafters, bu

overlapping them across the edges of the rafters. 

arrangement, concealed by the panels, created several 

along the 5-m distance separating the sewer vent pipe 

the light fixture at the apex of the attic, but reducin

total gap to a few centimetres - an easy side-

scenario, resulting in the ignition of the dust and su

fizz ofthe rough-fiom-sawmill~rafters. 

The second observation, a few days after the inci

was to notice a small rust spot on the kitchen sink wher

kettle usually sat: there was a small hole in the other

good-condition glaze, exposing the underlying cast 

The flash seen under the kettle (0) was the cause o

enamel puncture; several kilovolts must have been requ

to break down the series-connected insulation of the he

element inside the kettle, and the porcelain glaze o

sink. The electronic ground-fault circuit breaker contro

the receptacle had to be reset, but it was not damaged

subsequent use of the kettle did not cause it to trip, s

concluded that the brief breakdown of the insulation o

heating element was not a massive event. 

The immediate action was to install a bond betwee

sewer vent pipe and all extraneous metal in the attic. 

long-term effect on the engineer was a consciousn

raising on the issue of surge protection of multiple-

appliances, even though a bond had been provided betw

the incoming cable TV service and the power system [5

that time, the concept of the surge-reference equalize

had not yet surfaced, and no commercial device 

available to provide that function. In fact, the prolifera

of plug-in surge-protective devices launched by 

introduction of metal-oxide varistors had not yet occu

A casual inspection of the fist-sized surge arrest

the service panel showed no distress, an indicatio

adequate design for the rare scenario of a direct strike 

building [7]. 
This arrester used only a 30-mm diameter silicon 

carbide disk as varistor, which most likely would be 

destroyed by the high-energy lightning surges presently 

considered or recommended by some IEC committees. 

(Sorry, the house has changed owners and an exhaustive 

test on that particular surge arrester, desirable as it would 

be in retrospective, is not possible.) 

The attic side-flash (@ in Figure 4) clearly indicated 

that the sewer vent pipe was the point of strike (a), raising 

the question- of why the tall trees failed in their expected 

mission of establishing an effective cone of protection. 

Perhaps one explanation might be that during the initial part 

of the rainfall, the still-dry trees could not emit a successful 

competing upward streamer, compared to the wellgrounded cast-iron pipe. Comments from lightning physics 

experts on this speculation would be welcome. 

Thus, our engineer had learned his lesson, and lived 

happily without further incident for fifteen more years in 

the far-away land. However one cannot say 'lived happily 

ever after' : After moving to a new home further South, 

one night a nearby lightning flash triggered a burglar alarm 

(which had to be pried open to silence the horn turned on 

by a failed semiconductor, at 02:OO am no less) and 

damaged a remote-control garage door opener: Zeus had 

still kept track of the battle-hardened surge-protection 

engineer, but that is another story ... 

5. FROM REALITY TO SIMULATION 

Among several investigations based on rockettriggered lightning, the ongoing effort at Camp Blanding in 

Florida, U.S.A. is aimed at injecting a lightning current at 

specific points of the replica of a residential power system. 

Initial results (1997) were inconclusive because of 

instrumentation problems, but as these are progressively 

overcome, more definitive information becomes available. 

Actually, the most recent report [8] provides so many raw 

measurement results that an effort of synthesis will be 

necessary to gain a better understanding of the issues. 

The major advantage of such systematic projects over 

a random recitation of anecdotes could be the possibility of 

goirrg frum a real-world cdguratio~~ to a sufficiently 

detailed numerical representation of the circuit parameters. 

A cross-validation of the measurement results and of the 

simulation results would then significantly increase the 

credibility of both, and lead to realistic designs and ratings 

for SPDs. 

The challenge, of course, will be to represent enough 

of the many, many parameters involved in the real world 

but not so many as to make the simulation model 

unmanageable. For instance, the real-world situation of 

the anecdote already simplified in Figure 4 - with the 

ill-defined bonds and side-flashes - would be difficult to 

turn into a manageable and credible simulation. 

6. DISCUSSION 

The simplified assumptions on lightning cur

dispersion illusPated in Section 2 have met with so

skepticism among the North-American surge-protec

community and perhaps others. Part of this skepticism 

also based on the relatively rare occurrence of mas

failures for secondary arresters (distribution transfor

secondary terminals and residential service entran

designed to withstand the "classical" 8/20 ps or 4/10 

surges, at crest levels of a few to a few tens of kiloampe

Furthermore, the two simulations cited in Section 2 w

based on the assumption that earthing electrodes hav

constant resistance during the flow of the lightning curr

an assumption that is questioned on the basis of prelimin

results of measurements made in Florida in connection w

triggered lightning experiments [8]. 

In contrast with these simplified scenarios, the r

word anecdote would be a challenge for any numer

modelling but demonstrates evidence of substan

overvoltages developed in the* installation (insula

puncture at the kettle) during the flow of this undetermi

lightning current dispersion among the complex availa

paths to earth. The anecdote also offers an example 

surge arrester with modest current-handling capabi

surviving the scenario of a direct strike to a building. 

A symptom of the incomplete consensus is 

noticeable lack of a discussion of risk analysis in the rep

developed by the IEC Joint Working Group [2]. This to

was initially included in the document outline, rais

high expectations, but, confronted with incompat

proposals, the group gave up on that initiative. T

proposed methodologies ranged from elaborate and deta

mathematical formulae - which turned out to be us

somewhat arbitrary postulates - to common-sense, alm

intuitive considerations. 

7. A PROPOSAL FOR THE DISPERSION 

OF LIGHTNING INFORMATION 

In a 1963 freedom-seeking speech that still resona

today, the mantra "l'hve a dream" was coined. On a m

more modest scale, the author has a dream of unfette

information-sharing on lightning. Having cited 

preceding examples of developing, but still incompl

consensus on the dispersion of lightning current, here is 

proposal (or is it a challenge ?): Hopefully helpful tim

participation, on a world-wide basis via electronic m

could supplement - not compete with - the establis

routes for information sharing, at a much accelerated pa

We are still mostly in a mode of developing standards 

a notoriously slow process - by volunteers or deleg

often hampered by travel budgets, or of publishing pe

reviewed papers - unquestionably a wise process, 

entailing long delays between generation and ultim

publication of the information. 
This process of information dispersion might take one 

of the many forms by which the Internet has revolutionised 

information sharing. Should this paper be accepted for oral 

presentation at the Conference, the author would propose 

to make only a very brief summary of the paper itself - available to all in print - and make use of the scheduled 

presentation time for a cross-pollination of ideas among the 

attendees (much superior to the one-on-one poster process) 

on how to implement the proposal, bringing reality to the 

dream. Pessimists will point out hurdles such as the 

requirement of ''previously unpublished information" for 

later acceptance of an archival paper reporting research on 

the subject, or the understandable modesty of researchers 

who want to be sure that the work is complete before 

publishing even preliminary results, and so forth. Optimists 

will find ways to by-pass these hurdles and broaden an 

early consensus. 

CONCLUSIONS 

While there is no disagreement, or at least very little 

skepticism, on the specific parameters of the lightning 

discharge, consensus on the implications of lightning 

current dispersion for the rating of surge-protective 

devices has not yet been reached. 

Anecdotal information offered in many countries on 

their experience with service entrance surge-protective 

devices having moderate handling capability suggests 

that the proposed ratings for very high duty levels 

might be unnecessary and not cost-effective, unless a 

convincing risk analysis demonstrates otherwise. 

Information dispersion on these issues could be greatly 

enhanced by establishing an informal and timesensitive world-wide site (in parallel, not in conflict 

with more formal procedures), which the author is 

prepared to undertake if encouraged and supported by 

colleagues in the lightning-protection community. 

REFERENCES 

9.1 General 

Many publishing organizations, in their instructions for 

the peer-review process, raise the question "Are references 

adequate to show knowledge of work by others?" or words 

to that effect. While undoubtedly a valid question, the 

result is sometimes a lengthy recitation of up to several 

hundred citations, which seems an overkill. 

Standard-writing organizations have evolved the 

concept of differentiating between, on the one hand 

"References" - a listing of documents that are made an 

integral part of the standard by a ritual introductory 

statement, and, on the other hand, citatio~~ - in the form 

of a "Bibliography" with or without annotations. 

For this paper, "References" are limited to the s

minimum necessary to support a particular point be

made. To illustrate where extensive listing of "referenc

might lead, a likrature search was conducted w

"lightning" as a leading key word, and next with 

additional word. The results are listed below, showing 

number of "hits" found for the period of just 1969-199

the accessible on-line data base did not include Benja

Franklin's seminal letters to the Royal Society on lightn

protection of houses and the Purfleet munitions storage 

Lightning 15 791 

Lightning + surge 2348 

Lightning + current 3306 

Lightning + damage 1130 

Lightning + protection 6349 

Lightning + arrester 1816 

Lightning + earth + electrode 139 

These numbers show that it would be unrealistic f

single researcher to examine in detail the contents of fift

thousand papers. Injecting the concerted filtering 

sharing action of today's active researchers into a rea

accessible data base - the author's dream - would b

great improvement. 

9.2 Specific references 

[I] Anderson, R.B. and Eriksson, A.J.. "Lightning paramet

for engineering applications." ELECTRA, No.69, Marc

1980. 

[2] IEC 62066: 2000, General basic information regardin

surge overvoltages and surge protection in low-voltage 

ax. power circuits. 

131 Mansoor, A. and Martzloff, ED., 'The Effect of Neutra

Earthing Practices on Lightning Current Dispersion in 

Low-Voltage Installation," IEEE Transactions PWRD

July 1998. 

[4] Key, T.S., Nastasi, D., Phipps, K.O., and Martzloff, F.D

"Some enlightening case histories on lightning damage

Submitted for presentation at ICLP 2000. September 2

[5] Key, T.S., and Martzloff. F.D., "Surging the Upside-Do

House: Looking into Upsetting Reference Voltages," 

Proceedings, PQA '94 Conference, Amsterdam, Octobe

1995. 

[a] IEEE Std I 100-1999 ("Emerald Book") IEEE 

Recommended Practice for Powering and Grounding 

Electronic Equipment. IEEE, 1999. 

[71 IEEE PC62.41.1-2000 - Drafi IEEE Guide on the Surg

Environment in Low-Voltage (I000 Vand less) AC Pow

Circuits. 

[8] EPRI "Investig?tion of lightning entry into a secondar

service using rocket-triggered lightning," EPRI Report 

TR-110418, April 1998. 

[9] Cavendish. Watson. Franklin and Robertson, "A report 

of the Committee appointed by the Royal Society 

to consider a Method jor securing the Powder 

Magazines at Purjleet," Philosophical Transactio

of the Royal Society, London, 1772.