1

 1967 IEEE Conference papers were available at the meeting for $0.75 and later for $1.00. 

 However, they became no longer available some time thereafter.

Filename: Residential surges

All rights reserved IEEE

Reprinted, with permission, from 

IEEE Conference paper 31 CP 67-4301

Significance:

Part 3 – Recorded occurrences

One of the first papers reporting surge recording in low-voltage ac power circuits.

Both waveform information and frequency of occurrence marked the beginning of the IEEE effort toward

characterizing surge voltages in low-voltage ac power circuits, a departure from the traditional unidirectional

and separate 1.2/50 and 8/20 waveforms in use for high-voltage equipment testing.

In the mid-sixties, when these recordings took place, there were very few, if any, surge-protective devices

(SPDs) installed in residential power circuits. After the emergence of ubiquitous consumer-type SPDs, the

results of subsequent monitoring campaigns were drastically changed (See “Galore” in Part 2) but the

information is still valid for the frequency of occurrences to the extent that the origins of surges have not

changed, only the observed levels are now considerably reduced by the proliferation of SPDs.
Paper No. 

31 CP 67-430 

Conference Paper 

SWE VOLTAGES IN RESIDENTIAL, POWER CIRCUITS 

F. D. Martzloff 

Manber IEEE 

Both of: 

General Electric Ccmpany 

Schenectady, N. Y. 

A paper recurmended by the IEEE Pmtective Devices Carmittee of th

IEEE Power Group for presentation at the IEEE Scnmer Fbwer Meeting

brtland, Ore. , July 9-14, 1967. Manuscript subnitted April 3, 1

made available for printing May 3, 1967. 

- Price: $1.00 

(759 at meeting) 

(15C per copy additional if 

first class mailing desired) 

(254 per copy additional if 

air mail is desired) 

All Rights Reserved by 

The Institute of Electrical and Electronics Engine

Inc., 

345 East 47th Street 

New York, N. Y. 10017 

Litho in USA 
SURGE VOLTAGES IN RESIDENTIAL POWER CIRCUITS 

by 

G.J. Hahn and F.D. Martzloff 

Research and Development Center 

General Electric Company 

Schenectady, New York 

Abstract 

Special instrumentation was developed for 

monitoring the magnitude and frequency of occurrence of surge voltages in residential circuits. 

Over a period of two years, more than 400 

locations in 20 cities were surveyed. Monitoring 

was accomplished by automatic recording cathode 

ray oscilloscopes and simple surge counters. 

Two significant sources of surge voltages 

were identified: load switching within the house, 

and external surges, most likely associated with 

lightning, coming through the service drop. 

Internally generated surges as high as 2500 

volts were recorded during this test program, and 

six of the 250 households (i.e., 2.4 percent) in 

the sample experienced surges of this type in excess of 1200 volts once or more per day. A statistical evaluation indicated that a 90 percent 

confidence interval for the true proportion of 

homes with such surge voltages is between 1.0 and 

4.7 percent. 

Surges due to lightning reaching 5600 volts 

have been recorded on a 120-volt overhead distribution line. Independent evidence shows the 

occurrence of a number of surges in excess of 

2000 volts. 

In this study, a total of. 8 surges in excess 

of 1200 volts were caused by lightning and recorded on 39 counters at room outlets in 14 localities over the summer months. 

Introduction 

The successful operation of semiconductors 

and new insulation systems in appliances and consumer electronic devices may be adversely affected 

by transient overvoltages occurring on the 120- 

volt power supply. Detection and measurement of 

these transient surges permits a designer to provide suitable built-in tolerance, or at least to 

recognize that there is a need for appropriate 

suppression or protection,* 

Special instrumentation has been developed 

for detection and measurement of surge voltages. 

In the first phase of testing automatic recording cathode ray oscilloscopes provided complete 

information on wave shape, and on magnitude and 

frequency of occurrence at a small number of 

arbitrarily chosen locations. These data, though 

statistically restricted, were adequate to demonstrate the existence of the problem, define some 

sources, and indicate typical wave shapes. It 

also became clear that there was a need for a 

larger sample that would be more statistically 

valid. 

In the second phase of testing, one hund

surge counters, simple in design and easy to 

stall, were developed especially for this prog

These counters were installed in several hund

homes in various cities located in the East an

middle West of the United States. 

The purpose of this paper is to discuss 

cordings obtained during the two phases of th

program and the statistical aspects of the re

It is hoped that publication of this paper wi

encourage other investigators to publish thei

findings. This would provide a broader stati

tical base for verification of the frequency 

magnitude of surge voltages. 

Instrumentation 

Recording surge voltages in the field po

special problems. For example, the instrumen

cannot be continually attended and the signal

be recorded are unpredictable in magnitude, p

ity, and frequency of occurrence. 

In cooperation with Tektronix, Incorpora

a type 515 cathode ray oscilloscope was modif

to record transients on film, with automatic 

vance of the film after a recording. 

The modifications involved a change in th

trigger and sweep circuits, as well as remova

all knobs (an important detail for an instrum

to be left in all types of locations). 

Most oscilloscope trigger circuits are p

ized. This often causes a loss of recording 

the polarity of the initial signal is not kno

For surge recording, the trigger circuit was 

ified by feeding to the time base trigger thro

two OR logic diodes the push-pull signal that 

applied to the input of the oscilloscope dela

line. With this modification, the sweep is 

started for either polarity, while the signal 

delayed before reaching the deflection plate 

the CRT. In addition, the conventional blank

circuit holds the beam in low intensity befor

the sweep starts. 

A second modification changed the sweep 

a constant speed to a logarithmic speed, fast 

the start and slow toward the end. This allow

the recording of an impulse front with good r

lution, while providing sufficient duration o

the sweep to record a long tail. 
Finally, a relay was added with its coil 

energized whenever the beam sweep is triggered. 

Through a set of contacts on this relay, the film 

advance sequence in the camera is activated. 

The camera, attached to the scope bezel, is 

a Beattie-Coleman system, accommodating 100 feet 

of 35 mm film, with no shutter, and recording on 

a 24 x 36 nun frame the trace displayed on the CRT. 

Following the sweep, the contact mentioned above 

closes the motor circuit, advancing the film to 

the next frame in a few seconds. This film transport duration is matched in the oscilloscope trigger circuit by a hold-off so tliat no sweep will 

occur during film advance. 

In order to prevent the film from being 

fogged by extended exposure to the faint glow on 

the phosphor (caused by imperfect blanking of the 

beam, cathode glow or light leaks) a built-in 

timer in the oscilloscope advances the film by one 

frame every hour. This provides an approximate 

method for timing the occurrence of surges. Since 

the surge-voltage tests were conducted, an automatic time recording feature has been added to 

give a more precise recording of time at each 

event. 

Figure 1 is a photograph of this oscilloscope 

camera system. The relatively high cost of this 

system, its conspicuous presence (e.g., size, 

camera noise, etc.) in a home, and the amount of 

film to be scrutinized frame by frame limit the 

number of locations at which recordings can be 

made. However, for conclusions to rest on a sound 

statistical basis, it is necessary to investigate 

a large number of locations. To be acceptable to 

cooperative home owners, a transient detector 

should therefore lend itself to inconspicuous installation and simple data handling. Thus, a device which can merely be plugged into a wall 

receptacle, and that has a digital counter indicating the number of surges occurring above a 

specified threshold is satisfactory for widespread 

recording. 

The circuit shown in Figure 2 was developed 

for the purpose, and packaged as shown in Figure 

3. This device is connected to a wall receptacle 

by a conventional appliance cord, not a special 

probe. This connection is simple, establishes a 

typical final path for a surge impinging upon any 

appliance connected to this particular wall receptacle, and provides power for the high impedance rectifier circuit and a signal input to 

the trigger-sensor circuit. 

A crudely compensated divider (RlCl/R2C2) 

attenuates the incoming surge before application 

to the Silicon Symmetrical Switch (SSS). This device has the characteristic of turning on abruptly 

whenever the voltage across it reaches a threshold, such as 250 volts. This threshold remains 

constant for durations as short as 0.1 s. When 

the SSS turns on, the attenuated surge is applied 

to the gate of the very sensitive, fast switching 

Silicon Controlled Switch (SCS). If the polarity 

of this surge is positive, the SCS turns on, 

allowing the capacitor C to discharge through 

coil of the solenoid-actuated counter S. A h

impedance (50,000 ohm) divider and half-wave 

tifier provide a trickle charge 15-volt suppl

the capacitor C. The resistance of this divi

represents a negligible load for the house wi

system, yet is sufficiently low to allow some 

leakage in the electrolytic capacitor C. The 

charging time (several seconds) of the capaci

is not objectionable, since the transients to 

detected do not have a high repetition rate. 

Calibration of the circuit is obtained b

justing the value of the divider (RlCl/R2C2). 

these tests, the threshold level was set at 1

volts for one group of counters and at 2000 v

for another group. A bench circuit was set u

whereby a surge with adjustable level and dur

could be superimposed on a 60 Hz, 120-volt po

supply. Some consideration was given to the 

to segregate, or filter out, the surge from t

60 Hz power voltage; in this case, however, w

the minimum level at 1200 volts, the base 170

crest represented a small contribution and wa

cluded in the signal detected by the circuit. 

Surges with approximately flat top and duratio

from several microseconds to 0.2 microsecond 

applied to determine the variation of the thr

old voltage as a function of surge duration. 

typical response curve is shown in Figure 4. 

response of this crest-indicating counter can 

considered satisfactory, since the oscillosco

recordings in homes, as will be discussed lat

have indicated that the shortest half-period 

oscillatory surges is in the order of 2 micro

seconds. 

Recording Procedure 

In the first phase, oscilloscopes were i

stalled at the basement service entrance of h

in the Schenectady, New York area. These loc

do not represent a statistician's ideal sampl

but, during the initial phase of the program, 

nature of transients rather than statistical 

racy was the major subject of interest. Late

the program, the range of locations was broad

to include homes in other urban and rural are

particularly in Florida and South Carolina. 

In the second phase, surge counters were 

stalled at unspecified outlets in the homes o

engineers in 20 cities in the northeast and m

west. Two distinct recording periods were sc

uled: winter, because there is usually a mini

of lightning activity at that time of year, a

summer, which ordinarily includes a mziximum o

lightning activity. 

Since the oscilloscope input circuit ope

at a level of a few volts, it is somewhat sen

to direct radiation of electromagnetic noise 

the preamplifier, even if there is no signal 

the probe. In order to discriminate against 

type of spurious indication, the recording pr

cedure included a period during which the osc

scope probe was shorted with the ground termi

remaining connected, so that spurious signals 
to ground loops would be detected. In this manner, any noise entering the system could be recorded and later recognized for what it was in 

the analysis of the recordings made with the short 

circuit removed from the probe. 

The surge counters record only one polarity; 

in order to minimize record keeping by the homeowner, the connection of the cord was not polarized. In the event of an oscillatory surge (which 

is always quickly damped in these systems) two 

cases of counting can occur. For instance, the 

high side of the divider can be connected to the 

"hot" terminal of the receptacle (Figure 5). If 

the first half -cycle is positive and exceeds 1200 

volts, a count is registered. If the first halfcycle is negative, and the second, positive half 

is highly damped, no count is registered. If the 

first half-cycle is well above 1200 volts causing 

the second half, in spite of some damping, to exceed 1200 volts, a count is registered. For the 

reverse connection, the same would occur for reverse polarity. Thus, the actual number of surge 

occurrences of both polarities in excess of 1200 

volts is between 1 and 2 times the number indicated by the counter. The objective of the recording in this test series was only to determine 

whether or not surges occurred rather than their 

exact number. Consequently, the value of the 

multiplying factor is not very significant. 

Results Of The Recordings - Oscilloscopes 

The first recording analysis revealed that 

some homes were subject to frequent surge voltages, some experienced only a few isolated surges, 

and others did not experience any surges in excess 

of the trigger level (300 to 400 volts). Furthermore, among those installations where surge voltages frequently occurred, the surges at same 

houses were relatively low (rarely in excess of 

800 volts), while other houses had surges in the 

range of 1200 to 2500 volts. 

Rates of surge occurrence ranged from zero 

(no surge in one to two weeks) to 0.5 per hour, 

with peak values from 400 volts (trigger threshold) to 5600 volts. 

At the conclusion of the recording program, 

a total of 16 homes and two overhead distribution 

poles had been monitored for a total of 7000 

hours. The peak of the surges was distributed as 

shown in Figure 6a; the most frequent and severe 

surges were distributed as shown in Figure 6b. 

Further analysis of some recordings was made 

by deliberate switching of loads in the houses 

where frequent surges had been observed. In some 

cases, the operation of a specific device (e.g., 

oil burner, fluorescent lamp, pump motor, refrigerator, food mixer, etc.) was found to be the 

cause of the surges. In other cases, no amount of 

deliberate load switching could reproduce surges 

such as those recorded during unattended monitoring. The home owner was occasionally able to 

correlate surge recordings with lightning or 

power system disturbances. 

A pattern emerged from all this informat

showing two definite causes of surge voltages

the homes: 

1. Load switching in the house occasion

produced transient surges; these affected 

only that particular house. For any par

ular house, these transient surges had a 

shape which was consistently repeated wi

variations in amplitude along the entire 

recording. This probably resulted from c

bination of switch characteristics and th

impedance of the house wiring system; the 

variations in amplitude were probably cau

by variations of the switching angle and

connected loads. Typical wave shapes of 

recorded surges are shown in Figures 7a, 

and 7c. 

In one case, it was possible to inst

an oscilloscope in a house adjacent to th

where repetitive surges up to 1700 volts 

being recorded. The service drops were c

nected to the same pole, yet no surges o

ring simultaneously were recorded in the 

second house. 

2. Surge voltages not associated with lo

switching within the house were associate

with lightning storms. In some cases, th

home owner was able to correlate the film 

vance counts with the storm. Although re

corded during lightning storms at two di

ent locations, the surges shown in Figure

8a and 8b present the interesting charac

istic of being oscillatory at a frequency 

the range of 300 kHz. The surge shown in 

Figure 8a was recorded-at the overhead d

tribution line (oscilloscope mounted on t

pole), while the surge of Figure 8b was r

corded at the service entrance in a home

The first exhibits far less damping than 

second; this might be explained by the lo

damping due to lower resistance of the sy

tem at the pole than at the end of a serv

drop. 

Both of these surges, as well as most of 

other surges recorded during lightning storms

exhibit this oscillatory characteristic at a 

quency which,is nearly constant for a particu

locality. This constancy suggests that the o

lation of the system followed an excitation ca

by the lightning stroke. A number of surges 

the range of 800 to 1200 volts were observed d

ing several storms. The maximum surge voltage 

recorded was 5600 volts; several other surges 

corded during the same period were in excess o

4000 volts. 1 

Results of The Recordings - Counters 

With the two causes of transients identi

by the oscilloscope measurements, the surge 

counters wee applied in two separate program

First, during the winter months, the counters 

installed in a large number of houses for peri

of one or two weeks; the objective was to 
determine how many houses sustained repetitive 

surges. Second, during spring, summer, and fall, 

each counter was left at one or two locations for 

periods of 9 to 48 weeks; it was known from the 

first test that these homes were not subject to 

load switching surges. The objective was to determine the frequency and characteristics of externally generated surges, presumably caused by 

1 ightning . 

The first period produced the data shown in 

Table 1, and the results obtained during the 

second period are shown in Table 2. 

Statistical Analysis of The Recordings 

Internally Generated Surges 

The data in Table 1 show that 6 houses, or 

2.4 percent, were subjected to repetitive surges 

from among a total of 250 homes sampled. The 

true percentage doubtless differs somewhat from 

2.4 percent due to statistical variations. However, one may be 90 percent confident that the 

true percentage is between 1.0 percent and 4.7 

percent.* This band could be narrowed by taking 

additional samples. However, it should be noted 

that the precision is proportional to the square 

root of the sample size. Thus, four times the 

number sampled, or 1000 homes, would be necessary 

to cut the size of the statistical error band by 

approximately one-half. Since the above results 

refer to statistical variations only, they do not 

take into account possible biases due to such 

factors as restrictions in selecting members of 

the sample (principally engineers in a number of 

designated locations) or the time of year (winter 

months ) . 

The probability of internally generated surges 

undoubtedly varies among e.conomic groupings (i.e., 

the devices in use in homes probably vary with the 

economic status of the resident); however, devices 

found to generate surges (i.e. , furnaces, refrigerators, etc.) exist in most homes. 

Externally Generated Surges 

Results from the second testing period that 

was concerned with externally generated surges are 

shown in Table 2. From 39 counters installed in 

a total of 91 homes in 14 localities, a total of 

8 occurrences in 6 separate localities were observed during an equivalent exposure time of 846 

weeks. A ninth occurrence was disregarded in this 

analysis because it occurred in the same home during the same storm. Of the two pairs of occurrences which took place in the same location, one 

pair occurred during the same storm and the second 

involved two occurrences at different times. 

 his result is obtained by the well-known method 

of setting confidence intervals for a sample percentage. Further details may be found in statistical te~ts.~,3.4 

Analyses could be conducted based on the 

following alternative assumptions: 

1. Voltage surges above 1200 volts occur 

only during the period of the year that t

counters were installed in the homes. Th

although the counters were in homes for o

part of the year, the time involved (i.e.

the summer months) was so chosen that no 

ther surges would have been noted even if 

each counter had been run for 52 consecut

weeks. The average number of surges per 

would then be 8/39, or 0.205. 

2. Voltage surges occur randomly at a co

stant rate throughout the year. Thus, a 

counter which was in use 9 weeks, on the 

average, would be subject to a third as m

surges as a counter in use for a period o

weeks. Under this assumption, a total of 

surges observed in a total time equivalen

16 years (846 weeks) ~ields an average of 

surges per year. 

Using these tuo extreme assumptions, a ra

could be established for the estimated number 

surges per year in a larger sample, based on t

specific sample, The above calculations refer 

only to single polarity surges. If all surges 

being considered, the given values must be mu

plied by a value corresponding to the addition

proportion of opposite polarity surges above 1

volts which do not also result in positive sur

above 1200 volts. This multiplying factor is 

probably about 1.6; it accounts for the dampin

between the first and second 1/2 cycle of an o

latory surge. 

Lightning-induced surges are likely to af

more than one house when they occur. Local ge

graphical and meteorological conditions are cr

cal influences on these surges; however, these 

factors could not be considered in this prelim

investigation, 

To relate the above data to risk of appli

failure, the given values must be modified by 

probability that a surge above 1200 volts woul

cause failure of operating appliances. Failur

effects would vary with different appliances. 

Possible Further Analysis 

A more refined analysis for a probability 

measurement of voltage surges per lightning st

is possible if the geographical location of th

homes, the occurrence rate of lightning storms 

during the testing period, and exact dates at 

voltage surges occur is considered. The resul

values can then be used in conjunction with in

formation given in Reference 5 to calculate th

probability of a voltage surge in any specifie

geographic area, during a particular part of t

year. Such an analysis would remove the need 

making one of the two alternative assumptions 

stated above and lead to a single set of estim

However, this would require more detailed data 

could be collected in this program. 
Finally, it is noted that if one has knowledge of the actual voltage surges, rather than 

merely the information concerning whether or not 

a surge above 1200 volts occurred, a more sensitive analysis is possible. In this case, for 

example, probability plotting and other techniques 

based upon the statistical theory of extreme 

values4 3 might well be applicable. 

Effects of Surge-Voltages 

On Connected Electrical Devices 

The surges which have been recorded in this 

program occurred during normal operation of the 

household, with no knowledge of the connected load 

situation at the time of occurrence. 

The question of energy involved in the surge 

is related to the impedance of the system, since 

these recordings provide voltage data only. Surge 

impedance measurements of house wiring cable indicate a value of 100 to 300 ohms for a typical 

branch circuit, so that the surge impedance at the 

service entrance could be in the order of 5 to 10 

ohms. However, this low value exists only for the 

travel time (i.e., a fraction of a microsecond). 

Connected loads will have a lower impedance than 

that of the branch circuit. This value will be 

dependent upon frequency whenever inductive components are present. These loads will absorb part 

of the energy of the surges and thus lower their 

peak. 

Ikvices such as motors and transformers have 

solid insulation and such a long history of successful application that their performance is not 

in question. Perhaps unusual failures can be explained by extreme values of surges as indicated 

by the data. 

Defective wiring practices (e.g., pinched 

insulation, reduced air clearances in wall boxes, ' 

etc.) will cause air flashover with or without 60 

Hz power follow. In fact, one house was brought 

to our attention because of complaints of sparking 

in a light fixture. With the switch in the ground 

wire and the frame attached to a grounded pipe, 

flashover at 1700 volts was observed in correlation with the start of an oil burner in the house. 

This defective light fixture was acting as a voltage limiting gap for the house. 

Appliances containing semiconductors and directly exposed to the line transients may be more 

vulnerable. Actually, the 1200-volt threshold 

level was selected as the result of this consideration. It is interesting to note that, although a 

number of surges above 2000 volts were recorded by 

the oscilloscopes, the few surge counters calibrated for 2000 rather than 1200 volts did not 

produce any recording above 2000 volts. 

An independent study of clock motor failures 

produced information on failure rates versus withstand levels. This study was very pertinent to 

the surge counter program, since thousands of 

clocks are connected a t a l l times to the power 

system. Over a period of three years, failure 

rates were correlated with insulation level of 

coils. A very significant 100 to 1 drop in fa

ure rate resulted from an increase in withstand 

voltage from approximately 2000 to approximate

6000 volts. This shows that, even though no 

surges over 2000 volts were recorded by the 20

volt counters, surges in excess of 2000 volts d

indeed occur. 

Conc lus ions 

1. Residential power circuits are subjec

to surge voltages due to two distinct cau

load switching within the house, and exte

nally generated surges that are most like

associated with lightning. 

2. Internally generated surges caused by 

load switching are likely to be repetitive

They can generally be associated with a 

specific device, probably operating errat

ically or exciting some natural frequency 

the wiring system. They are not related 

lightning or disturbances from the utility

Peaks as- high as 2500 volts have been observed. The best single statistical estim

is that 2.4 percent of households of the 

sampled experience these internally gener

repetitive surges in excess of 1200 volts

However, because of the statistical varia

ity in the sample, this value may be as lo

as 1 percent or as high as 4.7 percent. 

Surges may be repeated several times a da

3. The frequency of surges caused by lig

ning is not affected by household electric

devices, but rather by local geographical 

and meteorological conditions. The limite

data in this program reveal several light

ning-caused surge occurrences above 3000 

volts with one reaching 5600 volts. 

4. Independent evidence shows that a sig

icant number of surges above 2000 volts d

occur periodically in residential power li

Acknowledgments 

The contribution of the hundreds of indiv

uals involved in the data collection and the c

tribution of J.E. Lenz for the data on overhea

distribution lines are gratefully acknowledged

References 

Lenz, James E. , "Basic Impulse Insulation 

Levels of Mercury Lamp Ballast for Outdoor 

Applications,'' (Discussion), Illuminating 

gineering, February 1964, pp. 133-140. 

Dixon, W.J. and Massey, F.J., Jr., Introdu

tion to Statistical Analysis, McGraw-Hill, 

New York, 1957. 

Bowker, A.H. and Liberman, G.J., Engineeri

Statistics, Psentice-Hall, New Jersey, 195
J. Czech, Oscilloscope Measuring Techniques, New 

York, Philips Technical Library, Springer-Verlag, 

1965. 

O.H. Davie and J. Wood, "An Automatic Cathode-ray 

Oscilloscope Beam Brightening Device for Transient 

R.D. Goldblum, ''Measuring DC Relay Coil Transients," Electronic Industries, Vol. 24, April 

1965, pp. 68-71. 

~ecordin~s," Journal of scientific Instruments, 

Vol. 33, No. 5, May 1956, p. 203. 
Figure 1. Oscilloscope and Camera 

Figure 3a. Surge Counter--Cover Removed 

Figure 3b. Surge Counter Elements--Removed fr

Shield 

I I 1 1 1 I 1 

0.2 0.4 0.6 0.8 1.0 I .2 

DURATION OF FLAT TOP PULSE . microseconds 

Figure 4. Response of Surge Counter 
ffl 

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Figure 7a. Internal Switching Transient Recorded 

at a Farmhouse (15 such transient surges in 1500 

hours) 

Figure 7b. Composite Record Showing Surges for a 

24-hour Period at a Suburban Home. (Oscilloscope 

is triggered for each surge, plus once every hour, 

resulting in 2 165-volt band of steady state 60 Hz 

voltage. Recordings above 1800 volts are blanked 

out by the oscilloscope.) 

Figure 7c. Single 

corded at the Same 

5-day period surge

corded as follows: 

1500 volts,21 abov

volts. Source was 

a high-voltage tra
0 5 10 20 30 40 psee 75 100 

Figure 8a. Transient Surges Recorded on Overhead 

Distribution Systems in Charleston, South Carolina 

(3800-volt crest, 300 kHz oscillatFon.)