Part 4 – Propagation and coupling — Numerical simulations 

Most simulations performed to investigate the sharing (dispersion) of lightning current for the case of a direct flash to 

a building have focused on the role and stress of surge-protective devices (SPDs) installed at the service entrance of 

a building and their involvement in that part of the lightning current that exits the building via the power supply 

connection to the energy supply. 

The numerical simulations performed for this paper, based on a postulated waveform and amplitude suggested by 

current standards, include downstream SPDs, either incorporated in equipment or provided by the building occupant. 

The results show that a significant part of the exiting lightning current can involve those downstream SPDs with some 

likelihood that their surge withstand capability might be exceeded. Such a possibility then raises questions on the 

validity of the postulated amplitude in the face of the relatively rare occurrence of reported failures. 

Filename: Role of SPDs
THE ROLE AND STRESS OF SURGE-PROTECTIVE DEVICES 

IN SHARING LIGHTNING CURRENT

François D. Martzloff 

National Institute of Standards and Technology 1

Gaithersburg MD 20877 USA 

f.martzloff@ieee.org

Arshad Mansoor 

EPRI PEAC Corp. 

942 Corridor Park Blvd 

Knoxville TN 37932 USA 

 

1 Contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.

Abstract – This paper examines the sharing of lightning current associated with a direct flash to a 

building. This sharing involves not just those surgeprotective devices (SPDs) that might be installed at the 

service entrance, but also all SPDs involved in the exit 

path of the lightning current. Such sharing might 

involve built-in SPDs of some equipment located close to the service entrance, but heretofore not included in 

numerical simulations performed by many researchers. From the numerical simulations reported in this paper, 

conclusions are offered that may influence the design 

and EMC testing of equipment, as well as the risk 

analysis associated with lightning protection. 

I. BACKGROUND AND RATIONALE 

This paper offers additional information to the body of 

knowledge accumulated on how the lightning current of a direct flash, injected into the earthing system of a building, is shared among the many available paths 

towards intended or opportunistic earthing electrodes. 

Recent developments in the International Electrotechnical Commission (IEC) and the Surge-Protective 

Devices (SPD) Committee of the Institute of Electronics 

and Electrical Engineers (IEEE) have focused on the role of SPDs connected at the service entrance of a 

building in the case of a direct lightning flash to the 

building. This scenario is described in IEC 61312-3 

(2000) [9], IEEE PC62.41.1 [12] and PC62.41.2 [13]. 

Prior to this new focus, most of the considerations on 

SPD applications were based on the scenario of surges 

impinging upon the service entrance of a building as 

they come from sources external to the building. The new (additional) focus addresses the scenario of the 

earth-seeking lightning current as it is shared among the 

many possible paths to earth, including the deliberate 

and opportunistic exit paths of the building earthing 

system, services other than the power system 

connection and, mostly, the power supply connection. 

Quite independently from these lightning protection 

considerations, the IEC Subcommittee SC77B had 

developed a series of documents on the electromagnetic 

compatibility of equipment, IEC 61000-4-5, Surge 

withstand capability [8] in particular. These documents 

were primarily concerned with immunity against typical 

disturbances, the rare case of a direct lightning flash to a 

building containing electronic equipment not included. 

Increasing recognition of the need to include the 

scenario of a direct flash to a building – rare as it might 

be – has motivated the formation of an IEC Joint Task 

Force TC81/SC77B for the purpose of considering 

surge stresses on equipment higher than those currently 

described in the IEC document 61000-4-5 on immunity 

testing [8]. 

The purpose of the paper is to examine in detail the 

sharing of lightning current, not just by the SPDs at the 

service entrance, but also by all SPDs that might be 

involved in the exit path of the lightning current. Such 

sharing might well involve SPDs incorporated in the 

equipment located close to the service entrance, but not 

always included in the numerical simulations that have 

been performed by many researchers (Altmaier et al., 

1992) [1]; (Standler, 1992) [23]; (Rakotomalala, 1994) 

[20]; (Birkl et al., 1996) [3]; (Mansoor and Martzloff, 

1998) [15]; (Mata et al., 2002) [19]. In its recent 

development of a Guide and a Recommended Practice 

on surges in low-voltage ac power circuits [13] the 

IEEE has refrained from identifying SPDs as being 

those that may be connected at the service entrance. 

Instead, it refers to "SPDs involved in the exit path" 

without reference to their point of installation. 

Given the tendency of equipment manufacturers to 

include an SPD at the equipment power input port, the 

issue of "cascade coordination" arises. Several previous 

papers (Martzloff, 1980) [17]; (Goedde et al., 1990) 

[5]; (Lai and Martzloff, 1991) [14]; (Standler, 1991) 

[22]; (Hostfet et al., 1992) [7]; (Hasse et al., 1994) [6] 

have explored the concept of cascade coordination 

involving two or more SPDs connected on the same 

power supply but at some distance from each other. 

The legitimate wish of the energy service providers to 

specify robust SPDs at the service entrance results in 

SPDs having a relatively high Maximum Continuous 

Operating Voltage (MCOV). On the other hand, some 

equipment manufacturers tend to select SPDs with a 

low MCOV under the misconception that lower is better 

(Martzloff and Leedy, 1989) [18]. This dichotomy can 

result in a situation where the low-MCOV SPDs 

included in equipment might well become involved in 

the "exit path" and thus become overstressed in the case 

of a direct flash to the building. This situation is made 

more complicated by the fact that commercial SPDs 

packages are assembled from typical distributors' supplies that can have an allowable tolerance band of 

±10% on the voltage-limiting rating. 

To explore the possibility and implications of a 

questionable coordination, numerical simulations were 

performed on a simplified model of a building featuring 

SPDs installed at the service entrance and SPDs that 

may be incorporated in equipment connected inside the building near the service entrance. 
II. NUMERICAL SIMULATIONS 

II.1 Basic circuit 

Figure 1 shows a simplified building power system that 

includes the key elements of this scenario: the building 

earthing system and all earthing electrodes, with the 

corresponding exit paths via the service-entrance SPDs 

and a built-in SPD provided at the power port of a 

typical item of electronic equipment. In this example, 

these SPDs are metal-oxide varistors (MOVs) with 

typical voltage ratings (150 V at the service entrance 

and 130 V in the equipment) selected for a 120/240 V 

residential power system. (The conclusions obtained 

for this type of power system will also be applicable to 

240/400 V systems.) 

Numerical analysis of the circuit behavior by EMTP [4] 

allows inclusion of the SPD characteristics as well as 

the significant R and L elements of the wiring, with 

injection of a stroke current of 100 kA 10/350 μs at any 

selected point – the earthing system in this case. The 

selection of a 100 kA peak is consistent with the 

postulate made in many published simulations, but 

might be questioned on the basis of field experience and 

lightning detection statistics, as will be discussed later 

in this paper. 

In Figure 1, the neutral is defined as part of a "multiplegrounded neutral" system (TN-C-S), with distributed R 

and L elements between its earthing electrode 

connections. The R and L values for the cables used in 

the numerical simulation, but not shown in the figure to 

avoid clutter, were selected to emulate the typical wire 

diameters used in low-voltage power distribution 

systems and building installations. 

Previous studies (Birkl et al., 1996) [3]; (Mansoor and 

Martzloff, 1998) [15] have validated the intuitive 

expectation that the tail of the 10/350 μs waveform 

often postulated for simulations will be shared among 

the available paths simply according to the relative 

values of resistance in the paths leading to the earthing 

electrodes. This fact is apparent in the results of Figure 

2, for example at the 350 μs time: when inductive 

effects have dwindled, the current IH in the 10-Ω

earthing resistance of the building is ten times smaller 

than the total current exiting the building [IN+IL1+IL2] 

toward the power distribution system in which multiple 

earthing electrodes offer an effective earthing resistance 

of only 1 Ω. It is also worthy to note that this sharing is 

controlled by the relative values of the resistances, so 

that any earth conductivity differences associated with 

local conditions will wash out. 

The combination of the service-entrance 150-V MOV 

on Line 2 and the 130-V MOV incorporated at the 

power port of the equipment constitutes a so-called 

"cascade". When two such cascaded SPDs are to be 

coordinated, a decoupling impedance must be provided 

between the two SPDs so that the voltage drop caused 

by the current flowing in the decoupling impedance – in 

this example the impedance of the 2,5 mm2

 diameter 

wires – and added to the limiting voltage of the 130-V 

MOV, will cause enough of the current to flow through 

the 150-V MOV to reduce stress on the 130-V MOV. 

The simulation was performed for three values of the 

impedance (length) of the connection, i.e., 0,1 m, 1 m, 

and 10 m to assess the effect of this impedance for 

practical situations. Figure 3 shows the results for 

these three cases and Table 1 shows the resulting energy 

deposition in the respective MOVs.

Figure 1 Simplified building schematic with service-entrance SPDs, one built-in equipment SPD, and 

multiple-grounded power distribution system in case of a direct lightning flash to the earthing system
0

20

40

60

80

100

120

0 100 200 300 400 500

IN

IH IL1 & IL2

Io (100 kA 10/350)

Legend 

IO: 100 kA, 10/350 μs stroke to the building earthing system 

IN: current exiting via the neutral of the power supply 

IL1, IL2: current exiting via the two lines of the power supply 

IH: current into the building earthing electrode(s) 

Vertical scale: current in kA – Horizontal scale: time in μs

Figure 2 – Sharing of the lightning current among 

available paths to earth electrodes 

In the traces of Figure 3, the total current in Line 2 (sum 

of the two currents in the two MOVs) remains 

essentially unchanged for the three combinations, but 

the sharing of the current between the two MOVs is 

significantly affected. 

Figure 3a, with only 0,1 m of separation, is not a 

practical example of connection of equipment that close 

to the service entrance – except perhaps an electronic 

residual current device incorporated in the service 

panel. The two other figures, 3b and 3c, show how the 

130-V MOV that took the largest part of the current in 

the case of Figure 3a, now takes on less as separation 

length increases. An interesting situation develops as 

the current flowing in the 10-m line to the 130-V MOV 

stores energy that will cause a stretching of the current 

in the 130-V MOV long after the 150-V MOV current 

has decayed. This is significant because the total 

energy deposited in the MOVs is the criterion used for 

coordination, even though the current in the 130-V 

MOV could be lower than the current in the 150-V 

MOV. Table 1 shows how this energy sharing changes 

with the length of the decoupling connection, according 

to the integration of the varistor currents and voltages 

obtained from EMTP. 

Table 1 – Sharing energy between MOVs 

for three different connection lengths 

Energy deposition (joules) SPD 0,1 m 1 m 10 m 

150-V MOV 620 1090 2470 

130-V MOV 2560 2030 890 

These energy levels might be acceptable for a 150-V 

MOV sized for service entrance duty, but the 890-joule 

deposition into the 130-V MOV incorporated in the 

equipment exceeds common-wisdom ratings for such 

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000

IL2

Ie

IS2

a) 0,1 m connection 

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000

IL2

IS2

Ie

b) 1 m connection 

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000

IL2

IS2

Ie

c) 10 m connection

Legend 

IL2: current exiting via the power supply phase conductor 

IS2: current into the service entrance SPD 

Ie: current into the equipment SPD 

All vertical scales: current in kA 

All horizontal scales: time in μs

Figure 3 – Sharing of lightning stroke current 

devices. This finding then raises a question on the 

effectiveness of a cascade for the case of direct flash to 

the building. In an actual installation, there would be 

more than one piece of equipment, presumably each 

with a 130-V built-in MOV at the power port. One 

might expect that some sharing among these multiple 

SPDs would reduce the energy stress imposed on these 

devices. 
To explore this situation, an additional simulation was 

performed for three branch circuits, respectively 10 m, 

20 m, and 30 m, each of them supplying equipment 

incorporating a built-in 130-V MOV. Figure 4 shows 

the sharing of current among these three MOVs and the 

150-V service entrance MOV, and Table 2 shows the 

energy deposition. 

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000

IS2

Ie(10m) Ie(20m Ie(30m)

Legend 

IS2: current into the service entrance SPD 

Ie: currents in the three SPDs at end of 10, 20, and 30 m lines 

Vertical scale: current in kA – Horizontal scale: time in μs

Figure 4 – Sharing of current among MOVs 

Table 2 – Energy sharing among MOVs 

Branch circuit length and energy 

deposition into three 130-V MOVs 

10 m 20 m 30 m 

Service entrance 

150-V MOV 

620 J 370 J 280 J 1930 J 

 

II.2 Effect of manufacturing tolerances on 

commercial-grade metal-oxide varistors 

The simulations discussed so far were performed by 

postulating that both the 150-V MOV and the 130-V 

MOV had their measured voltage limiting at the 

nominal value as specified by typical manufacturer 

specifications. Such a postulate is of course difficult to 

ensure in the reality of commercial-grade devices. For 

instance, the nominal voltage-limiting value of MOVs 

rated 130 V rms is 200 V, with lower limit of 184 V and 

upper limit of 220 V. To check that aspect of the 

problem, an arbitrary lot of 300 devices rated 130 V rms 

was purchased from a distributor and the actual 

measured voltage-limiting value at 1 mA dc was determined in accordance with IEEE Std 62.33-1994 [11]. 

For this lot, the standard deviation (sigma) was found to 

be 8 V. 

 

On the basis on these measurements and to give an 

indication of the significance of tolerance effects, the 

computations reported for Figure 3c (10 m separation) 

were repeated, still with a 150 V MOV at the service 

entrance, but with varistors at ±1 sigma of the 130 V 

rms rating, that is, 122 V and 138 V rms. The results 

are shown in Table 3. 

Table 3 Energy sharing for three values of the 

equipment built-in MOV (10 m separation) Equipment Energy deposited (J) 

MOV rating 

(V rms) 

Equipment 

MOV 

150-V service 

entrance MOV 

122 915 2320 

130 890 2890 

138 750 2650 

These results illustrate the significance of tolerances in 

a situation where the difference between the two SPDs 

of the cascade is not large, because of the de facto 

situation of low values of MCOV that the industry has 

unfortunately adopted. Of course, if tolerances were 

also taken into consideration for the service entrance 

MOV, the extremes of distributions for both MOV 

would make an effective coordination between a 

nominal 150-V MOV and a nominal 130-V MOV even 

more problematic. 

 

II. 3 Nonlinearity of circuit elements 

 

Most of the reported simulations, as cited above, have 

been performed with a conservative postulate of a 100 

kA 10/350 lightning discharge. The median of the 

current peaks compiled in the seminal Berger et al. 

paper [2] is only 20 kA. Occasional reservations have 

been voiced on the validity of these data collected with 

technology dating back to the 1970’s. A recent (July 

2000) actual case history was communicated to the 

authors by a colleague for two major lightning storms 

recorded in the area of Tampa in Florida by means of 

the Lightning Detection System [24], during which over 

30 000 flashes were detected in a period of less than 12 

hours, with only one at the 150 kA level, and a median 

of 20 kA, confirming the Berger at al. data. 

One could expect that the dispersion of the lightning 

current that results from the combined action of linear 

elements (resistance and inductance) with nonlinear 

components (MOVs) might produce a different sharing 

of the current as the decoupling element is linear but the 

SPDs are nonlinear. To explore this hypothesis, the 

computations for the case of Figure 4 and Table 2 were 

repeated, for peak currents of 100 kA (the original value 

of the computation), 50 kA, and 25 kA (about the 

median of the statistics). Table 4 shows the results of 

these computations. It is interesting to note that as the 

applied stroke is decreased 4 to 1 (from 100 to 25), the 

total energy deposited in the varistors is decreased by a 

factor of 3200/610 = 5.2. This relative greater decrease 

is caused by the larger portion of the current exiting via 

the linear-path neutral, further relief for all the SPDs 

involved in the exit path. 

 Table 4 Nonlinear effects on current sharing 

Branch circuit length and 

energy deposited into 

three 130-V MOVs 

10/350

stroke 

(kA) 10 m 20 m 30 m 

Energy 

into 

service 

entrance 

150-MOV 

Total 

energy 

in the 

MOVs 

100 620 J 370 J 280 J 1930 J 3200 J 

50 329 J 215 J 179 J 700 J 1423 J 

25 170 J 120 J 90 J 230 J 610 J 
III. DISCUSSION 

 

We have made all these computations based on 

postulating that the insulation levels are sufficient to 

prevent a flashover that would drastically affect the 

continuing energy deposition in the downstream SPDs. 

We have not included the limits of energy handling of 

the devices, which of course should be compared with 

computed deposited energy levels in a practical case. 

Another set of readings from the EMTP computations 

confirmed that the presence of SPDs at the critical 

points prevents such overvoltages from occurring (as 

long as the SPDs can carry the resulting currents) 

 

Not surprisingly, the results of the simulation confirm 

that the sharing of the lightning current occurs in 

inverse ratio of the resistances leading to the earthing 

electrodes after the initial phase of the 10/350 μs stroke. 

Likewise, one can expect that inductances will limit the 

current flow so that low-inductive paths, such as 

intended and opportunistic earth electrodes of the 

building itself, compared to the longer lines of the 

power supply, will carry a larger share of the total 

current during the initial phase of the current. This 

effect is clearly visible on the IH of Figure 2, for the 

relatively slow rise time of 10 μs of a first stroke. One 

may expect that for the subsequent strokes, or the 

flashes associated with triggered lightning experiments 

that have shorter rise times (Rakov et al., 2001) [21], 

this effect will be even more apparent. 

 

An important finding – predictable on a qualitative basis 

but heretofore not quantified for the case of a direct 

lightning flash to buildings containing electronic 

equipment – concerns the cascade coordination of builtin SPDs in the equipment. From the simple examples 

presented, it appears that a cascade of a robust serviceentrance SPD and a built-in SPD sized for limited 

energy-handling capability, according to the commonwisdom practice, might well be a delusion. 

A solution to the difficult coordination could be to 

replace the all-MOV SPD at the service entrance with a 

combined series gap-varistor device (Mansoor et al., 

1998) [16]. Such a device would also alleviate the 

concerns about the temporary overvoltage problems 

associated with MOV-only SPDs. Sparkover of the gap 

during the initial rise of the lightning current (when the 

coordination by means of the decoupling inductance 

occurs) will invite the remainder (continuing rise and 

tail) of the surge current exiting via SPDs to use the 

service entrance SPD rather than the simple and less 

robust built-in MOVs downstream. 

Last but not least, the practical question remains open 

on the need to provide surge protection against worst 

cases – the combined worst case of a direct flash to the 

building and the high-level 100 kA stroke, which is 

only at the 4% probability, according to the Berger et al. 

data [2] and even lower in the yet-anecdotal case of the 

Tampa Bay lightning storm [24]. The nonlinearity effect 

presented in II.3 adds further credibility to the overall 

need to make reasonable risk assessments of costeffectiveness before specifying high surge level 

requirements, both for the service entrance SPDs and 

for built-in SPDs in connected equipment. 

IV. CONCLUSIONS 

1. When accepting the postulate that the reference 

parameter of a direct lightning flash to a building should 

be a 10/350 μs current with a peak of 100 kA, the 

numerical simulations performed for a simplified 

system with one surge- protective device installed at the 

service entrance, and one or more built-in SPD in 

downstream equipment indicate that the downstream 

SPD is very likely to be overstressed and fail, most 

likely catastrophically. 

2. There are several possible explanations for the 

apparent contradiction between a prediction of downstream equipment failures based on this postulated 

lightning parameters, and equipment field experience 

that does not report such frequent failures, although of 

course anecdotes abound. 

• The occurrence of a direct flash to a building can 

cause such extensive damage that a post-mortem for 

investigating the specifics of a prevailing ineffective 

coordination is not performed at that time and the 

issue is ignored. 

• Enough uncontrolled clearance flashovers occur in 

the installation to provide significant relief for any atrisk SPDs incorporated in downstream equipment. 

• In an installation where many built-in or plug-in 

SPDs are present, the sharing illustrated by Figure 4, 

combined with a low probability of a 100 kA stroke, 

might reduce the stress on downstream devices to a 

value within their capability. In particular, many 

commercial plug-in SPDs advertise capabilities of 

hundreds of joules, unlike the 20 joules of a single 

MOV, which might be provided at the input port of 

electronic equipment. 

• Insufficient field failure data have been obtained, 

compiled, shared, and published to enable realistic 

assessment of frequency and severity of occurrences 

involving an unsuccessful cascade coordination. 

 

3. It is impractical at this point to mandate high energy 

handling capability for built-in SPDs. Such a move 

might meet with strong objections from manufacturers 

whose products have satisfactory field experience, and a 

risk analysis might show it to be not cost-effective. 

4. Economic and political realities related to the type 

and mission of the installations to be protected should 

be kept in mind. Clearly, mass-market applications 

such as cost-conscious consumers, in a framework of 

regulated or unregulated installations, are different from 

bottom-line-conscious industrial applications, and even 

more so in the case of national assets – be they cultural 

or military. 

5. Another approach for manufacturers might be to 

avoid placing low MCOV varistors at the input port of 

their equipment. Rather, they should select an SPD 

with an MCOV and resulting surge-protective level as 

high as their equipment can inherently stand. This is a 

“selfish” approach which is mentioned here halfseriously, half-facetiously: there are enough low MCOV 

SPDs installed by users or included in other equipment 

in a typical system that those unfortunate low-MCOV 

devices will take up the stress, leaving unscathed the 

equipment wisely provided with high MCOV SPDs! 
V. REFERENCES 

Note: The citations that appear in the text are listed here 

by alphabetical order of the lead author, not by 

chronological order of appearance in the text. 

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Simulation of Surge Voltage Protection in LowVoltage Systems,” Proceedings, 21st International 

Conference on Lightning Protection, Berlin 1992. 

[2] Berger, K., Anderson, R.B. and Kröniger, H., 

“Parameters of Lightning Flashes,” ELECTRA

No.41, 1975. 

[3] Birkl, J., Hasse, P., and Zahlmann, P., “Investigation 

of the Interaction of Lightning Currents with LowVoltage Installations and Their Related Threat 

Parameters,” Proceedings, 23rd International 

Conference on Lightning Protection, Firenze, 1996. 

[4] EPRI, “Electromagnetic Transients Program,” 

(EMTP), Version 2.0, Vol. 1: Main Program; Vol.2: 

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[5] Goedde, G.L., Marz, M.B. and Henry, D.C., 

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[6] Hasse, P., Zahlmann, P., Wiesinger, J., and 

Zischank, W., “Principle for an Advanced 

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[7] Hostfet, O.T., Hervland, T., Nansen, B., and Huse, 

J., “Coordination of Surge Protective Devices in 

Power Supply Systems: Needs for Secondary 

Protection,” Proceedings, 21th International 

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[8] IEC 61000-4-5 (2001) Electromagnetic 

Compatibility - Part 4: Testing and measurement 

techniques - Section 5: Surge immunity test.

[9] IEC/TS 61312-3 (2000) Protection against LEMP - 

Part 3: Requirements of Surge Protective Devices.

[10] IEC 61643-1 (2002) Surge protective devices 

connected to low-voltage power distribution systems 

- Part 1: Performance requirements and testing 

methods

[11] IEEE Std 62.33-1994 IEEE Standard Test 

Specifications for Varistor Surge-Protective 

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[12] IEEE C62.41.1-2002 Guide On The Surge 

Environment In Low-Voltage AC Power Circuits

[13] IEEE C62.41.2-2002 Recommended Practice on 

Characterization of Surges in Low-Voltage AC 

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versus Low- High,” IEEE Transactions IA-24, 

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[15] Mansoor, A. and Martzloff, F.D., “The Effect of 

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[16] Mansoor, A., Martzloff, F.D., and Phipps, K., 

“Gapped Arresters Revisited: A solution to 

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in Low-Voltage AC Power Circuits,” IEEE 

Transactions, PAS-99, 1980. 

[18] Martzloff, F.D. and Leedy, T.F., “Selecting 

Varistor Clamping Voltage: Lower is not Better !,” 

Proceedings, 8th International Zurich Symposium 

on EMC, 1989. 

[19] Mata, C.T., Fernandez, M.T., Rakov, V.A. and 

Uman, M.A., “EMTP Modeling of a Triggered 

Lightning Strike to the Phase Conductors of an 

Overhead Distribution Line,” IEEE Transactions 

PWRD, 2002.

[20] Rakotomalala, A., Rousseau, A., and Auriol, P., 

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Symposium on EMC, 1994. 

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C.T., Rambo, K.J., Stapleton, M.V. and Sutil, R.R., 

“Direct Lightning Strikes to the Lightning 

Protection System of a Residential Building,” IEEE 

Transactions PE-032PRD, 2001. 

[22] Standler, R.B., “Coordination of Surge Arresters 

and Suppressors for Use on Low-Voltage Mains,” 

Proceedings, 9th International Zürich Symposium 

on Electromagnetic Compatibility, 1991 

[23] Standler, R.B., “Calculations of Lightning Surge 

Currents Inside Buildings,” Proceedings, IEEE 

EMC Symposium, August 1992. 

[24] Waterer, S.F., Personal communication on the 

Lightning Storm in Tampa Bay Area, July 15, 

2000.