Significance

Part 4 – Propagation and coupling of surges

Part 6 – Tutorials

This paper was presented as a summary tutorial aimed at the French-speaking Canadian community to solicit their

comments on the development of the IEEE Std 587 Guide. The paper has been translated into English by the

author to make the English-speaking community aware of that paper, which served at that time as one output for

the release of the extensive test results that were reported in the 35-page GE Memo Report – still proprietary at that

time – “Lightning protection in residential AC wiring” (see Part 4 of the anthology). 

The tests were performed by injecting a simulated lightning flash current of unidirectional waveshape into the

grounding system of a simplified residential wiring system, and observing the coupling and induction of oscillatory

surges in the house wiring

Part 8 – Coordination of Cascaded SPDs

Excerpts from the complete test report found in this summary include a discussion of the performance of gapped

arresters, as well as MOVs installed at the service entrance, with coordination with an MOV installed at the end of

branch circuits.

Filename: Coordination 1978
COORDINATION OF OVERVOLTAGE PROTECTION 

IN LOW-VOLTAGE RESIDENTIAL SYSTEMS 

F.D. Martzloff 

General Electric Company 

Schenectady, NY 

INTRODUCTION 

The development of metal-oxide varistors has made possible a 

substantial improvement in the mitigation of overvoltages in 

residential, commercial or light industrial power systems. For 

instance, transient suppressors are now available that can be 

plugged into a wall receptacle, thus making possible the 

protection of appliances or electronic devices that might be 

damaged by overvoltages occurring in power systems [I]. 

However, due to economic considerations, these suppressors 

have only a limited capability for absorbing high current 

surges that may be associated with lightning strikes occurring 

nearby. Thus, one may ask whether the installation of a 

suppressor with limited capability might not pose a risk of 

failure or create a false sense of security. 

It is then worthwhile to examine what occurs in a building 

provided with suppressors having different capability, located 

at different points of the building. as a function of the surge 

current intensity imposed by the lightning strike. Furthermore, 

the combination of several suppressors may allow a 

coordinated protection for reliable operation, which it would 

be worthwhile to demonstrate. 

CIRCUIT MODEL 

Given the complexity of distribution networks and the 

nonlinear response of the suppressors [2], it would be 

&f&.!t tc c,~Ip te 6- the L&b4;cr the 

S?l&~~t~l a ~~~ent SU~P T~IIC it is maere tn J----- e-- ---9 

the extent that res&y ~aq &, maJefi& hy a phy&d m&e!, in 

make tests directly on the devices actually used in these 

buildings. Such tests have been performed at the High Voltage 

Laboratory of the General Electric Company in Pittsfield, MA. 

We injected, into a physical model, currents corresponding to 

lightning strikes amplitudes ranging from moderate to 

extremely high 131. 

A model of a typical building was wired with the components 

used in a residential building: triplen overhead service drop 

from the distribution transformer, downconductor to the 

revenue meter, connection to the service panel provided with 

circuit breakers, with four branch circuits ranging from 5 to 50 

meters and provided with a receptacle at the far end. 

Assuming a 100-kA strike on the primary distribution system, 

an extreme case in the probability of discharges [3], a current 

division is postulated as shown in Figure 1, resulting from the 

injection of 30 kA in the (grounded) neutral conductor 

supplying the building. 

This 30-kA value is predicated by assuming that the lightning 

current transfers from the primary conductors to the grounding 

network as a result of the operation of the arrester, or by a 

K.E. Crouch 

Lightning Technologies, Inc. 

Pittsfield, MA 

Figure 1. Distribution of the 100-kA current 

in the ground network near the building 

flashover from the phase conductor to the ground condu

the primary circuit, without involving the two conduc

the low-voltage distribution. Only the (grounded) 

conductor of the service drop is involved, with 70 kA f

through the grounding connection of the pole involve

toward the two adjacent poles. 

Figure 2 shows schematically the path of the 30-kA 

injected in the ground conductor to the building, as wel

mechanism for inducing currents and voltages in the 

model, mostly by electromagnetic coupling into th

formed by the service drop. 

PHASE WIRES 'MLSSENGLR' 

/ 

DlSTRlBUTlON 

TRANSFORMER 

RECLPIA":E 

VOLTAGE 

MEASURED 

RETURN BY 

- GROUND PLANE 

The complete circuit, including the surge generator a

instrumentation, is shown schematically in Figure 3

course, the usual precautions were taken in the setup (sh

room for the instrumentation, checks for interference, 

@ 1978 IEEE. Translated from the original French version which first appeared in Proceedings, 1978 IEEE Canadian Conferenc

on Communications and Power, 78CH1373-0, pp 451-454. Permission to copy without fee is granted by the Institute o

Electrical and Electronics Engineers if not made for direct commercial advantage. To copy otherwise, or to republish, require

a fee and specific permission. 
LIGHTNING 

CURRENT 

GENERATOR 

BUTION I MODEL HOUSE 

; \ SURGE ARRESTER 

I OR JUMPER WIRE 

I 

I 

SHIELDED 

INSTRUMENT 

ROOM 

I , GR ouND ;l~lMi~dl 1 

CURRENT f \ /PLANE 

PROBE 1 I f ! I '1 

P . rlpre 3. Schemaiic of the exprimenti circuit 

Figure 4 shows an example of the waveform of the injected 

current, a 10125 ps impulse, which is a conservative hypothesis for the current involved. Three different values of the 

peak current have been used in the tests, 1.5 kA, 10 kA, and 

30 kA. The first value, 1.5 kA, is the standard duty test for 

a secondary arrester, the second, 10 kA, is the standard 

withstand test, and the last, 30 kA, is a pessimistic level. 

Figure 4. Injected current 

TYPES OF SUPPRESSORS 

There are two types of commercially available suppressors: a 

surge arrester that can be installed on the service panel or at 

the point of anchoring the service drop, and a suppressor 

which is a plug-in device as previously mentioned. 

The surge arrester type, which has been used for many years 

but only in limited numbers, meets the performance standard 

for a secondary arrester [4], in particular a rating of 10 kA, 

8/20 ps surge. One of the reasons for the lack of market 

success of this suppressor is undoubtedly the fact that its 

installation must be contracted out to an electrician because it 

requires work on the live circuits inside the service panel. 

Furthermore, this type of arrester has a let-through of about 

2000 V, which is excessive for sensitive electronic appliances. 

Varistor discs with a 32 mm diameter are now available, but 

only as an industrial component (at this time). These discs 

have the capability of diverting the 10 kA required by the 

standard, md thus are excellent candidates for a serviceentrance arrester because they can clamp at voltages 

si6cantly lower than those of previously available arresters. 

In the tests that we performed, these discs turned out to be 

highly promising. 

The plug-in type, represented in our test series by GE 

VSP-1, contains a 14-mm diameter varistor, with a rat

6000 A and capable of absorbing a number of 3 kA 

during its service life. 

COORDINATION OF SUPPRESSORS 

In an installation where several surge suppressor

comected at different points of the system, the suppresso

the lowest clamping voltage will be called upon to "pr

the suppressor having a higher clamping voltage, by sp

over first or by preventing the second from sparking ove

reverse this situation, it is necessary that the voltage d

the wiring, produced by the current flowing in the 

suppressor and added to the clamping voltage of the 

exceed the operating voltage of the second. In the c

vg&~w, wh;rh hsp &-en dp~i~p& s@g!!y nrnrl~~

r------ 

clamping voltage, this situation may become critical. 

5 illustrates the arrangement where the VSP-1 might p

the HLP from sparking over if the clamping voltage 

VSP-1 is much lower than the sparkover voltage of the 

This situation is another motivation for the tests, to veri

coordination can be maintained between the suppress

practical applications. 

HLP I 

_* VSP-I 

\ 

Sparkover of HLP: V1 5 VZ + Ri + Ldildt 

All the current in VSP-1: V1 > VZ + Ri = Ldildt 

Figure 5. Coordination between two 

suppressors separated by an impedance 

During a first test series conducted at 30 kA, we quickly 

that sparkover occurs at many points in the circuit, ma

difficult to obtain reproducible results. It was necess

reduce the current to 1.5 kA to reach a situation wh

sparkover would occur. Even at "only" 10 kA, sparkov

occurred in the unprotected devices (receptacle, service p

It should be noted that these sparkovers taking place be

the conductors (black to white or black to green) result 

from injecting current in the ground conductor of the c

not from injecting the surge directly into the phase condu

Many oscillograms were recorded, which cann

reproduced in this paper. Some examples are given 

following figures, to enable comparisons among the v

... 

arrannementr ..-. Of !he sgpp,,nTpSgO,,nTr, ShowLqa that an eff

b""'""" b ------ 

protextion scheme can be achieved, if only a few preca

are taken. 

Effect of the inductance at the end of the line 

Oscillograms 204, 247, and 248 (Figure 6) sho

attenuation obtained from an impedance at the end of th

for a 1.5 kA injection, at the end of a 25-m line. Oscill

204 shows an opencircuit voltage reaching 2200 V

oscillations at about 500 kHz decaying in about 20 ps. 
Open-circuit 

Voltage 

500 Vldiv 

2 psldiv 

Voltage with 

1304 load 

500 Vldiv 

2 psldiv 

Voltage and current 

in the VSP-1 with 

130 $2 and VSP-I 

Figure 6. Effect of impedance at the end of the line 

By connecting a resistive load of 130 il at that point, the 

voltage is reduced down to 1400 V, and the oscillations are 

replaced by a damped waveform. Adding a varistor (VSP-1) 

to the 130-R resistor produces the clamping shown in oscillogram 248; this oscillogram also shows that only 15 A flow in 

the varistor. From these oscillograms, the following conclusions' may be drawn: an oscillatory voltage at 500 kHz is 

induced in the line, superimposed to the unidirectional voltage 

produced by the injection of an unidirectional current. This 

osciiaiory voitage appears to be the resuit of osciilations 

&-Ciiiruig . . iii the he, "sci&iions i'nai can be &,peci by 

addkg a i&s:ive !od at the eii of the he. Furthermore, 

connecting a 130-Q resistor at the end of the line reduces the 

voltage at the end of the line from 2200 to 1400 V. One may 

view this situation as a voltage divider consisting of the source 

impedance and the impedance at the end of the line. A rough 

estimation of the "source" impedance, Zs, may be made by 

neglecting the complex nature of the impedances. The circuit 

equation may be written as Vr = Vo 130/(130 + Zs), where 

Vr is the voltage (1400 V) recorded with a resistor in the 

circuit, ad Vo is the open-circuit voltage (2200 V). Solving 

for Zs yields Zs = 75 Q. This value, although inaccurate 

because the equation was not vectorial, is nevertheless a useful 

result to provide an order of magnitude for the source imp&- 

ance, the perennial question. 

?~rf=EE?iXe ~f Siiiiiii&3SOiS ii: :he sei-<ice eiiiimce 

Osciiograms 143, 261, 263, and 153 (Figure 7) show the 

resuiis obtained by instaiiing various types of suppressors at 

the service panel, for a 10 kA surge. Without any protection 

(oscillogram 143), the voltage reaches 7 kV before collapsing 

to small oscillations. This collapse is actually the result of a 

breakdown occurring at some other point of the circuit, as 

demonstrated in other tests. This oscillogram shows that 7 kV 

peaks may be reached when no protection is provided. 

Voltage without 

protection 

2 kVldiv 

2 ps/div 

Varistor on 

the outside 

500 Ndiv 

500 Vldiv 

2 p/div 

Varistor on 

the inside 

500 Ndiv 

500 Vidiv 

2 psldiv 

HLP Arrester 

400 Aldiv 

500 Vldiv 

2 pldiv 

Fiyre 7. Compared performance of various 

suppressors at the service panel 

By installing a 32-mm disk outside the service pa

arrangement that requires a total of about 50 cm of wir

protective level shown in Oscillogram 263 is obtaine

800 V, with high-frequency oscillations reaching 

while about 1100 A flow in the disc. If the disc is co

directly onto the bus bars of the panel, with a m

connection length of about 15 cm, the protective 

substantially improved: oscillogram 261 shows oscilla

only 900 V and subsequent value of 600 V, with a cu

about 1200 A in the disc. In contrast, the HLP 

(oscillogram 153), which contains a spark gap and 

carbide varistors, allows the voltage to reach 2400 V 

sparking over, then holds a discharge voltage of abou

with a peak current of i'3W A. This set of measu

shows how important it is to hoid the connections as 

-- - -1L 1. rm~ ~ -- psslula. imey also show how ihe new metai-oxide v

c;;;; ;?;piGve pioiEtioii, if coiieci;y inshiid. 

Stress on the sxivvressors 

Considering the limited capability of the VSP-1 devic

is only a 14-mm disc and does not purport to be a l

arrester, it is interesting to determine the stress that m

imposed by injecting a surge with extreme value. 
-- 77 .mm dice ---- incirlp. 

Voltage and current 

for VSP-1 at 12 m 

500 Ndiv 

500 Vldiv 

2 jcsldiv 

32-mm disc outside 

Voltage and current 

for VSP-1 at 12 m 

200 Aldiv 

500 Vldiv 

2 pldiv 

No protection on the panel 

Voltage and current 

for VSP-1 at 12 m 

1000 Aldiv 

500 Vldiv 

2 pldiv 

No protection on the panel 

Voltage and current 

for VSP-1 at 25 m 

lo00 Ndiv 

500 Vldiv 

2 psldiv 

Figure 8. Stresses on the suppressors 

Figure 8 shows the resuits of tests made with an appropriate 

protection at the service panel (oscillogram 275), with a poor 

protection at the service panel (281), and without any protection at the service panel (283 and 284). 

With a disc connected directly across the bus bars (275), the 

ideal situation, the current in a VSP-1 located 12 m away from 

the service panel, resulting from injecting 30 kA, is less than 

400 A; the voltage across its terminals, to be applied to the 

protected load, is less than 500 V. If now the disc is installed 

outside of the panel (281), a reduction of the effectiveness of 

the protection, the current in the VSP-1 is slightly increased, 

with a corresponding increase in the clamping voltage. If no 

protection is installed at the service panel (283), the VSP-1 

would tend to absorb all the current, in this case a 3.3-kA 

peak with a clamping voltage of 650 V for a VSP-1 installed 

12 m away. In contrast, for a VSP-1 installed 25 m away, the 

voltage drop between the panel and the VSP-1, associated with 

the line impedance, is such that a breakdown occurs upstream 

from the receptacle (in this case in a parallel branch circuit), 

hence the limiting effect shown in oscillogram 284. 

Thus, this set of measurements shows that even in the extreme 

case of injected currents, the current imposed to the VSP-1 

remains within acceptable limits for a limited number of 

r..-=-.- Ttr atLn ,F -?i) A at QI?n ,re allnnrr rmnc;r

UUl(jW. 1IU 1.U.116 VI VVVV A L ULC "I lV y UYV r.0 WIY-U

-. limit ef A f~t &e pr411rt be, W;th high tel

Furtkrmore; this example illustrates the fact that bre

can occur in a poorly coordinated installation. From th

of view of the safety of the VSP-1, the breakdown sh

oscillogram 284 might be viewed as a safety valve, b

the overall safety point of view, it is not recommended 

upon a breakdown occurring in the wiring or at the te

of the wiring devices, because such breakdown may in

power fault with significant fire hazard. 

CONCLUSIONS 

1. It is sufficient to inject, in the ground conductor 

service drop, a surge current corresponding to a m

lightning stroke to reach Mous voltages between th

and neutral conductors within the building. 

2. Commercially available protective devices are cap

limiting overvoltages to acceptable limits; even in the 

an injection corresponding to extreme vaiues, severai a

ments may be considered: 

a) A lightning arrester consisting of a spark g

silicon carbide varistors can limit the overvoltages to 

2000 V, eliminating the risk of breakdown in the wir

the attendant fire hazard. This 2000 V limit provides 

tion for conventional appliances but may be inadeq

protect electronic devices that tend to be more sensitiv

b) A metal-oxide varistor, presently available 

an industrial component package, correctly installed 

service panel (short connections) would be sufficient 

overvoltages for all the building, even for high am

lightning strokes. 

b) A varistor with limited capability, the 

installed at a particular receptacle, will limit overvolt

ihai point to vaiues that are ac~eptabie fur eitxirmik &

---:A -A&..:-- :~--tr ---- ",.a *- L--..- -.." WIL~UC mug IISZU G.xpua- tu -du- auGaa, if ik d

L- , -,,- ..A+ --.;--.A ... ;th .,rn+-t;nn - ;C 

~&"ili a -=! - I'"% quy- " .LY p"L-.'VU - - '0 61-V. 

chut !G mes. T;nr &stmeS, t& ~n

-rr

the VSP-1 might exceed the expected reliability, with 

of the varistor. This failure would still provide pro

during the surge, but lead to a trip of the panel break

course, if a protection according to (b) were provi

would not be necessaty to install a VSP-I. If the pro

provided at the service panel is less than ideal (HL

addition of a VSP-1 at the receptacles that supply se

devices would provide protection for these devices, w

HLP would provide diversion of high currents. 

REFERENCES 

[I] Surge Voltages in Residential and Mustrial 

Circuits, F.D. Mrutzloff and G.J. Hahn, IEEE Trans

PAS Vol 89, pp 1049-1056, July/August 1970. 

[3] A Ground Lighming Environment for Engineering 

N. Cianos & E.T. Pierce, Stanford Research Institute, 

Park CA, August 1972. 

[4] Surge Arresters for Alternating-Current Power C

ANSI C62.1-1975. 

Certified translation by French Associates, Inc, Gaithersburg MD 20877. 

4