performed to narrow down the range of stresses to which the field-damaged equipment were submitted.

These case histories also illustrate the consequences of incorrect bonding of utility connections to one

residence, the sensitivity of dispersed electronic systems in the second residence, and incorrect routing of

earthing conductors in the third residence.

In a laboratory replica of this configuration [2], a 

peak voltage of 4,3 kV was recorded across the two ports 

for a typical surge injected at the telephone entrance. A 

similar situation exists for a surge impinging on the video 

port of a TV receiver. The tests reported in 2.3 below 

show that this level can cause damage. 

2.2 Cozy cabin site configuration 

In the Cozy Cabin installation, the power service 

entrance was located at one end of the house, while the 

cable TV service entrance was located at the opposite end. 

Furthermore, a visit to the site revealed that the cable TV 

shield was grounded only by a questionable ground rod 

next to the house foundation (within the drip line, and 

thus in dry soil, see Figure 2). This cable TV grounding 

electrode was not bonded to the grounding electrode of 

the power service entrance, a clear violation of the U.S. 

National Electrical Code ("NEC", NFPA 70, 1999) [4]. 

Following the visit to the site by the authors, the local 

cable TV company was informed of this situation and took 

what they believed an appropriate action: the incoming 

cable was first routed under the house, in the crawl space, 

to allow bonding the shield to the power service grounding 

connection. From there, the cable was returned to its 

original point of entry into the house, at the opposite end. 

This modification did correct the NEC violation but left 

the arrangement in the topology shown in Figure 1. 

However, the interaction was not pursued further 

with the cable company. A recommendation was made to 

the owner, to install a surge reference equalizer [5] for 

each piece of video equipment. After that was done, no 

damage occurred during the next lightning season. Of 

course, it is still too early to declare victory over Zeus 

and Murphy, but encouraging when compared to a 

previous history of two incidents within a few months. 

I I. Incoming cable 2. Splitter & discharge unit I 

2.3 Post mortem and surge tests 

One of the failed TV receivers from the Cozy Cabin 

was made available to the authors for examination. No 

evidence of damage was found on the power side of the 

chassis and the related components, but a clear indication 

of surface flashover was observed along the insulation of 

the gap intended to isolate the cable input 'ground' 

termination (connected to the incoming cable shield) from 

the shielding can of the tuner (connected to one of the 

power cord conductors, see Figure 3). 

After cleaning the carbonized path of the flashover, a 

0,5 ps - 100 kHz Ring Wave was applied in incremental 

steps between the two conductors of the power cord, 

bonded together, and the shield connector of the cable 

input: flashover occurred at 2 kV. By removing the 

material to a greater depth and covering it with epoxy, the 

gap did withstand a greater level, and failed at 2,5 kV. 

That flashover occurred at another part of the original 

insulation, thus providing valid information on the original - 

withstand capability. - 

2.4 Conclusions from the Cozy Cabin 

This case study illustrates the classic situation of 

separate service entrances, compounded with incorrect 

bonding. The examination and test demonstrate that at 

least 2,5 kV were developed across the power port and the 

cable TV port of the receiver under a condition of distant 

or nearby lightning strike 

Another significant finding from this case history is 

the anecdotal confirmation of allegations that cable TV 

installation practices prevailing in many residential 

situations might be in violation of the U.S. National 

Electrical Code. This violation made even more 

hazardous the now well-recognized occurrence of 

undesirable separation of the service entrances. 

3. Grounding wire 4. Ground rod I I .Tuner box 2. Cable termination box 

5.Watering can (for plants, not ground rod!) 3. Insulating gap 4. Incoming cable connection 

Figure 2 - Cable TV entrance Figure 3 - Insulating gap at signal input 
3. INPUT ISOLATION PRACTICES 

Interest aroused by the Case of the Cozy Cabin led to 

a brief survey of what isolation schemes are applied by 

the manufacturers of video equipment. 

Televisions and VCRs are of a similar category of 

equipment in that they both have the same input ports: ac 

power, and video (antenna or cable), for which the 

'ground' reference can be raised to different potentials 

during a surge event. The power port has no direct 

connection to the equipment grounding conductor because 

a two-prong ac plug is used. However, at the service 

entrance, the neutral - one of the two conductors of the 

cord - is bonded to the ground bus of the service panel. 

The video input is referenced to ground via a connection 

to a grounding rod outside the residence and (per the NEC 

[4]), a bonding conductor. 

Manufacturers use various techniques to isolate these 

two ports from each other inside the equipment. Surge 

tests were conducted on five televisions and three VCRs 

to determine the voltage level at which spark-over would 

occur between the power port and the video port. Using 

a 0,5 ps - 100 Hz Ring Wave, incremental steps of 

500 V were applied between the power port and the shield 

of the video input port. 

The units that had isolation built into the video port 

sparked-over at the series capacitor of the video port. The 

breakdown voltage level was approximately 2,5 kV in 

these units. Units in which the power supply outputs were 

electrically isolated from the inputs via transformers fared 

better. One sample survived and performed normally 

after all surge tests. Physical size of the transformer 

seemed to have some impact on the results. Larger 

transformers seemed to tolerate surges better than smaller 

ones. 

Based on this small number of VCR samples, a 

general observation is that VCRs use power supply 

transformers as isolation, similar to the newer TV sets, 

and do not have isolation between the cable or antenna 

input and the tuner chassis. This type of isolation scheme 

withstood higher surge voltages than the isolating ring that 

can be found in older television sets and serving to isolate 

the chassis of the set from the ('grounded') shield of the 

signal cable. 

4. THE CASE OF THE RAMBLING RESIDENCE 

An expansive residential estate, located in the same 

general area as the Cozy Cabin, was the scene of a 

lightning incident where a tree adjacent to the house was 

struck (and subsequently died). Extensive damage was 

inflicted to the audio-video components that are connected 

to a central rack, and are located throughout the residence 

and its surroundings (large patio and swimming pool, with 

outdoor lighting and audio speakers). 

The home owners graciously allowed the authors to 

visit the residence and observe the configuration of the 

system in an attempt to better understand the mechanisms 

leading to the damage. They also made available to the 

authors the complement of damaged or presumed damaged 

equipment that had been replaced thanks to their insurance. 

Thus, this case history, unlike most lightning incidents, 

offered an unusual opportunity for documenting the process 

and consequences. 

Three activities were undertaken to better understand 

the mechanism and verify some hypotheses: 

Bench examination of returned equipment and surge 

testing of undamaged equipment; 

Site visit of the residence; 

Laboratory coupling of electric field stress into a 

remote speaker-to-amplifier connection. 

Bench Examination 

Bench tests for each electrical appliance began by 

plugging it into a 120-V a.c. outlet. Physical signs of 

normal operation were noted such as illuminated displays, 

response of controls, audiolvideo output. The equipment 

cover was removed for an internal inspection. In most of 

the equipment, physical damage such as a burned-out 

transistor was very apparent. Table 1 lists the home 

entertainment equipment that were submitted, and their 

condition. 

A signiticant finding was that all of the power supplies 

in the equipment were functional, indicating that the 

lightning surge either did not enter through the ac power 

port, or was not severe enough to cause damage to the 

power supplies. 

Table 1 Equipment submitted for bench tests 

a@. 

- 

1 

3 

2 Twelve-channel integration amplifier .- 

Indoor speaker -- - 

Indoor/outdoor speaker -- 

I Independent color TV receiver 

Equipment 

Stereo tunerlamplifier -. - 

Digital satellite system receiver 

Damage to power transistors - 

Woofer damaged 

Woofer damage on all but two units - 

No damage 

Condition 

Illuminated display was not working 

Damage to telephone control circuit 
The examination and, as appropriate, tests revealed 

the following conditions: 

Except for its non-operational display, the stereo 

tunerlamplifier appeared undamaged. 

The visible damage to the digital satellite receivers 

was nearly identical in all three units. Apparently, 

the surge had entered through the telephone port and 

had damaged the small surface-mount electronics that 

make up the modem circuit. However, because the 

satellite receivers could not be operated without their 

antenna and code-reading cards, the extent of the 

functional damage could not be determined 

The two 12-channel amplifiers had sustained damage 

to their output transistors that drive the speakers. 

The power supplies and fuses were not damaged. 

Furthermore, it was found that some speaker outputs 

were still operational. This situation suggested a 

possible mechanism that damaged only some of the 

output transistors, and therefore not attributable to a 

"power-line surge." In turn, that hypothesis was later 

verified by a laboratory test, as described in 4.3 

below. 

Speakers, tested by connecting them to an amplifier 

that was known to be functioning properly, were 

found to have their woofers damaged, but the 

tweeters still operational. 

Other electrical appliances in the house including 

television sets and VCRs not connected to the centralized 

system were not included in the returned package and 

therefore presumed as not damaged. This fmding 

confii the conclusion that the long leads interconnecting 

the distributed system components acted as energy 

collectors, feeding the induced voltages or currents into 

the communications ports of the equipment. 

4.2 Site Visit 

The purpose of the visit was to look for clues to 

explain the specific damage that was observed in some of 

the equipment. The following observations were made: 

Approximate distances between the lightning strike 

and affected equipment 

Location and grounding at the service entrances of 

cable TV, power, and telephone 

Other wiring and general installation practices 

The overall physical layout of the house, damaged 

tree, and electronic equipment are shown in Figure 4. The 

tree that was struck is much taller than the house and is the 

tallest of the trees in the immediate area. The bark was 

stripped from the tree trunk for most of its height. The tree 

trunk is only approximately 15 m from the house and even 

closer to the patio, where some of the audio speakers were 

installed. Outdoor speakers are also located in the pool 

area and connecting walkways. 

In the audio amplifiers, as noted above, the power 

supplies of the units were not damaged, but their output 

transistors that drive the speakers and the speakers themselves were damaged. Thus, it was speculated that the 

surge energy had been coupled into the speaker wires, 

which are probably very long and very near to the lightning 

strike, rather than as a "power-line surge." 

The visit to the installation verified this theory. The 

home entertainment equipment, including amplifiers, is 

centrally installed in the basement of the house. Speakers 

are iocared throughout rhe house, the patio, and the 

swimming pool area. The wire length between the outdoor 

speakers and the central amplifier is about 30 m, and some 

of the wires run within 10 m of the tree trunk. 

Cable and 

Utility terminals Telephone 

Two-story house 

over basement 

4 50 m (1 60 ft) * 

. Underground 

utilities 

Utilities entrance 

(Power, TV, Teleph 

Sprinkler controls 

Figure 4 

Schematic configuration of the Rambling Residence 
4.3 Laboratory Coupling of Electric Field 

To validate the hypothesis of a failure mechanism 

involving the coupling of electric field energy into the 

speaker wire run, a qualitative laboratory test was staged, 

using the surviving channel of the amplifier to drive a 

speaker. An audio signal from a tape deck was fed into 

the amplifier input to monitor its operation during the test. 

A conventional Marx impulse generator at the NET HighVoltage Laboratory was used to apply a 1,2150 ps highvoltage field between two parallel plates, each 2 m x 1 m. 

A length of 5 m of speaker wire feeding the audio output 

from the system audio amplifier was sandwiched between 

the two plastic foam sheets separating the lower 

(grounded) plate, to which the amplifier chassis was 

bonded, from the upper (impulsed) plate. The effective 

length of the wire was increased by connecting to each 

wire a piece of foil of about 0,02 m2, simulating the 

increased capacitance effect of about 50 m of wire. Both 

the amplifier and tape deck were isolated from the power 

supply ground by an uninterruptible power supply. 

The impulse was applied in increments. At 70 kV, a 

flashover occurred between the two plate edges, but not 

involving the speaker wire. Immediate failure of the 

amplifier output circuit was noted. Frem this anecdote, 

we conclude that the rapid field change associated with the 

flashover did have the capability to couple enough surge 

energy into the capacitance divider of wirelground plane 

and cause destructive failure of the output transistor 

effectively connected across that capacitance. Such a 

scenario can be considered a reasonable emulation of the 

circumstances surrounding the "Lightning Incident at the 

Rambling Residence. " 

4.4 Conclusions from the Rambling Residence 

The qualitative laboratory demonstration of coupling 

energy into the speaker wires provides one more piece of 

evidence that electronic appliances can be damaged by 

surges impacting their communications port, to the point 

that expecting protection by simple application of SPDs 

on the power port is not enough, and comprehensive 

protection is a necessity. In this case, there was no 

evidence of any damaging surge introduced by the power 

supply connection of the residence. 

5. THE CASE OF THE STANDARD SUBURBAN 

5.1 The aftermath 

In this case, which occurred in a suburban, semi-rural hilly 

area, the post-strike invest~gation revealed that the 

overhead service drop to the house (involving a span of 

about 20 m across the street) had been severed by melting 

at the point of strike. From there, the current traveled to 

the revenue meter (typically on the outside wall in U.S. 

practice), where a ground conductor is normally installed 

with a short run to the earthing electrode of the house. 

htead, according to the practice when constructed in the 

1970s, a cold water pipe was allowed to be the main 

earthing electrode. In this case, the conductor for the 

earthing electrode entered the garage and was routed 

upward near the ceiling with several bends before it was 

bonded to a copper water pipe. Without any better path to 

earth, the lightning current had apparently followed the 

same route, severing the bare conductor while seeking the 

well-grounded water pipe (see Figure 5). 

North side West side -- - 

Inside north wall 

Figure 5 - The Standard Suburban aftermath 
As shown in the photographs of Figure 5, the service 

entrances were overhead and without any direct path to 

earth. This type of installation would not be approved by 

current US practice, which requires a direct connection to 

a driven ground rod in addition to any other supplemental 

electrodes such as the cold water pipe. One of the main 

reasons that the practice was modified is the growing use 

of PVC or plastic water pipe. 

On a later visit, the engineers who made the first visit 

were allowed to visit the repaired h6use. Indeed, the new 

service grounding point includes not only the electric 

power but also the telephone and cable company. The 

new water piping is PVC, and a driven ground rod has 

been installed as the primary grounding electrode. 

This new arrangement (Figure 6) reflects a recently 

issued recommended practice [6] which, in addition to the 

NEC minimum requirements for safety, calls for intersystem bonding of all utilities serving a residence, and this 

by having all the utility connections next to each other. 

Ground To Senrice Panel 

INTERSYSTEM BONDING P 

Telephone Network 

lnterfaceDevice\ 

Signal 

Input 

To Ground Rods J 

The Care of the Rambling Residence and related tests 

illustrates that the often-cited "powerline surge" cause 

is not the only scenario responsible for appliance 

failures. Other ports of equipment, communication 

ports in particular, can be damaged by surges induced 

into the cables used for incoming or outgoing signals, 

and therefore need appropriate protection. 

The Case of the Standard Suburban shows that 

architects and builders have not fully understood the 

necessity of appropriate wiring and earthing practices. 

The same lack of understanding by some utility 

providers was also evident in the Case of the Cozy 

Cabin. 

The recommended practice of intersystem bonding at 

the service entrance described in this paper is 

compatible with the requirements of the U .S. National 

Electrical Code. Codes applicable in other countries 

might require a different arrangement, but the 

principles are the same. 

ACKNOWLEDGMENTS 

Resources for conducting these investigations were 

provided by the members of the Electric Power Research 

Institute. 

Lightning flash density data and comments on the 

manuscript were contributed by Kenneth Cummins of 

Global Atmospherics, Inc. 

The experiment on coupling energy into speaker wires, 

and a review of the manuscript were contributed by Gerald 

FitzPatrick. 

8. REFERENCES -- 

Figure 6 - Recommended intersystem bonding [l] Personal communication, Global Atmospherics, Inc. 

5.2 Conclusion from the Standard Suburban 

Architects and builders, guided by up-to-date codes, 

can provide appropriate grounding practices in new 

construction. Surge-protective devices at the service 

entrance can provide a path from ungrounded conductors 

and equalize voltages between these conductors. The 

practice is recommended as the first level of protection 

from surges in the exterior electrical environment. 

6. GENERAL CONCLUSIONS 

The Care of the Cozy Win and related tests confirm 

the need to pay attention to the problems associated 

with the surge protection of multi-port equipment. 

The solution of non-metallic communications media 

is not yet ready for the consumer market, but an 

effective mitigation approach is the surge reference 

equalizer. 

[2] Key, T.S.. and Martzloff, F.D., "Surging the 

Upside-Down House: Looking into Upsetting 

Reference Voltages," Proceedings, PQA '94 

Conference, Amsterdam, October 1995. 

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

Grady, W.M., "Surging the Upside-Down House: 

Measurements and Modeling Results," Proceedings, 

PQA'95 Conference, May 1995. 

[4] NFPA 70 - 1999, National Electrical Code, National 

Fire Protection Association, 1999. 

[5] IEEE Std 1100-1999 (Emerald Book) IEEE 

Recommended Practice for Powering and Grounding 

Electronic Equipment, IEEE, 1999. 

[6] EPRI PEAC , Recommended Practice for Protecting 

Residential Structures and Appliances Against 

Surges, Report PEAC.0545.R, EPRI PEAC 

Corporation, Knoxville, TN, 1999.