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NBSIR 81-2301

Field Circuit Breaker Tester

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Washington, DC 20234

May 1982

Final Report

QC

NO. 81-2301

1982

Prepared for Consumer Product Safety Commission

Washington, DC 20207

NBSIR 81-2301

FIELD CIRCUIT BREAKER TESTER

P. Michael Fulcomer

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Washington, DC 20234

May 1982

Final Report

Prepared for Consumer Product Safety Commission

Washington, DC 20207

U S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Foreword

The equipment and procedures described in this report were developed

in conjunction with, and for use by, the Consumer Product Safety Commission

(CPSC) to investigate the performance of circuit breakers in residential

installations. This report is intended to serve only as an instruction/maintenance manual for use by qualified CPSC staff in operating

and maintaining the test equipment. Neither the equipment nor the test

procedures are intended for general use.

Prior to conducting tests at a given site, test personnel are required

to unplug the electricity meter and plug a substitute meter base assembly

into the meter socket. With the substitute meter base properly installed,

the 240-V ac lines are disconnected from the circuit breaker panel and

connected through appropriate protective devices to the input unit of the

test equipment. During subsequent tests of the circuit breakers, low

voltage, constant-current ac voltage is supplied by the test equipment

through the meter socket to the circuit breaker panel.

The particular meter base supplied with the test equipment mates

with one type of meter socket that is commonly used in residential

installations. However, test personnel should be aware that other socket

configurations may be encountered in the field and should determine the

compatibility of components before arranging the tests.

Since the conduct of the tests involves breaking the seal and removal

of the meter, the use of unmetered electricity during the tests, and the

subsequent re-i nstal 1 ation and sealing of the meter, each test must be

planned with the full knowledge and approval of the local utility company

and other relevant authorities. Furthermore, to ensure the validity of

the test data, all phases of the tests should be carried out by qualified

personnel who have a thorough understanding of residential electrical

systems and equipment and of the procedures and equipment used in the

tests. Finally, and most importantly, since removal of the meter exposes

terminals with hazardous voltages, all general safety precautions plus

those specifically discussed in this manual must be rigorously observed.

In developing the equipment and test procedures, every effort has

been made to ensure the safety of operating personnel and to avoid damage

to the equipment under test. However, without direct supervision of the

tests, NBS cannot be held responsible for the accuracy of test results

nor for any damage or injuries that might be incurred.

It should be noted that the procedures are intended to be carried

out by a two-person crew. Even though the individual components of the

test apparatus can be manipulated by an average individual, prudent

operating practice requires the presence of a second person.
TABLE OF CONTENTS

Page

Foreword iii

LIST OF TABLES ....... ...... v

LIST OF FIGURES vi

1. INTRODUCTION 1

2. GENERAL DESCRIPTION ......... 2

3. SYSTEM OPERATION ................... 3

4. PREPARATIONS FOR TEST ....... ......... 9

5. OPERATING PROCEDURES . 13

6. CONSTRUCTION 17
LIST OF TABLES

Page

Table 1. Parts necessary to test circuit breakers in situ .... 19

Table 2. Weight of the various field circuit breaker

tester parts . 20

Table 3. Parts list for the Generator Input Unit (GIU) 21

Table 4. Parts list for the Generator Output Unit (GOU) 22

Table 5. Parts list for the Control Unit (CU) 23

Table 6. Parts list for the meter base assembly and the

probe assembly 24

Table 7. Parts list for the interconnecting cables 25

v
LIST OF FIGURES

Page

Figure 1. Block diagram of the field circuit breaker tester . . . . 26

Figure 2. Schematic diagram of the Generator Input Unit (GIU) . . . 27

Fi gure 3. Schematic diagram of the Generator Output Unit (GOU) . 28

Figure 4. Schematic diagram of the Control Unit (CU) . . 29

Figure 5. Generator Input and Generator Output Units . . 30

Figure 6. Control Unit ..................... . 30

Fi gure 7. Generator units mounted on a portable hand truck . . . . 31

Figure 8. Substitute meter assembly ........ . 31

Fi gure 9. Spring-loaded probe assembly ........ . 32

Figure 10. Schematic diagram of the comparator circuit . . 33

Fi gure 11 . Schematic diagram of the duo-monostable multivibrator

circuit . 33

Fi gure 12. Interconnecting cables ........ ... . 34

Figure 13. Field circuit breaker tester prepared for travel . . . . 34

Figure 14. Closeup of the spring-loaded probe contacting

a circuit breaker load terminal . . 35

Figure 15. Individual probe assembly parts ...... . 36

Figure 16. Probe assembly attached to a panel board . . 36

Fi gure 17. Interior view of the Generator Input Unit

(left side looking toward rear)

. 37

Figure 18. Interior view of the Generator Input Unit .......

(left side looking toward front)

. 38

Fi gure 19. Interior view of the Generator Input Unit .......

(right side looking toward front)

. 39

Fi gure 20. Interior view of the Generator Output Unit . (right side looking toward rear)

. 40

Fi gure 21

Interior view of the Generator Output Unit . (left side looking toward front)

. 41

vi
LIST OF FIGURES (cont.)

Page

Figure 22. Side view of the interior of the Control Unit 42

Figure 23. Rear view of the interior of the Control Unit 43

Figure 24. Interior view of the meter base assembly 44

(upper section)

Figure 25. Interior view of the meter base assembly 44

(lower section)

Figure 26. Rear view of the meter base assembly 45

vi i

FIELD CIRCUIT BREAKER TESTER

P. Michael Fulcomer

1. INTRODUCTION

Overcurrent protection devices are required within an electrical distribution system to minimize the possibility

of electrically initiated fires caused by circuit overloads.

Circuit breakers are the most commonly used form of overcurrent

protection in new and recent residential construction. However,

the complexity of the circuit opening mechanism typical of these

devices makes them susceptible to mechanical deteri oration

which can affect their operation. A circuit breaker so affected

may perform its intended function for a direct short type of

fault but may not respond adequately to a less severe circuit

overload condition.

The possibility that an unknown number of installed circuit

breakers might not perform as intended under certain overload

conditions prompted the Consumer Product Safety Commission (CPSC)

to initiate an investigative testing program. The program will

include visiting various field locations, subjecting installed

circuit breakers to controlled overcurrent conditions, and

evaluating their performance. In order to obtain valid field

performance data, the testing will be accomplished without

removing or otherwise disturbing the circuit breakers.

Test equipment developed at NBS for the CPSC to evaluate

the performance of single-pole circuit breakers in residential

installations is described in this report, along with instructions

for its use. The procedures are intended to be carried out by a test crew of at least two persons.

1
2. GENERAL DESCRIPTION

The field circuit breaker tester is designed to permit on-site

testing of installed single-pole circuit breakers! - primarily those

used in residential applications with 125-A (ampere) or smaller frame

size. The circuit breakers can be tested as already installed without

disturbing any of their connections. Testing is preceded by interrupting

the 240-V (volt) utility power to the panel board containing the circuit

breakers, then using the utility power to operate the circuit breaker tester.

The tester generates a constant test current for checking the breakers of

interest or all of them in sequence.

Interruption of utility company power is achieved at the service

entry by pulling the electric power meter. The meter is temporarily

replaced by a modified meter base assembly which feeds incoming 240 V ac from the upper jaws in the power company meter socket to the circuit

breaker tester by means of connecting wires. Constant current generated

by the tester is returned to the lower jaws of the meter socket through

the same meter base assembly and fed from there to the circuit breaker

panel board via the power company service entry cables.

The circuit breaker tester is basically a source of low voltage,

moderately high, constant current, the output duration of which is accurately

indicated by a self-contained timer. The output current is adjusted to

the desired value with all connecting wire resistance (but not breaker

resistance) in the circuit. The unit is started after the breaker to be

tested is added into the circuit. When the circuit breaker trips, output

current from the tester is automatically shut off. Elapsed time is

indicated and held on a digital panel meter (DPM) until the next test is

started.

The unit has two ranges of output (10 to 100 A and 30 to 300 A),

which permits increased instrumentation accuracy over the entire range.

The maximum voltage output from the instrument is approximately 11.5 V ac.

The required output voltage depends on the impedance through which

the circuit breaker current must flow. For example, if a test current of

200 A is desired (e.g., to test a 100-A circuit breaker at twice its

rated current) and the connecting wires and circuit breaker itself offer

a combined total impedance of 20 mfi (mi 1 1 i ohms ) , then the tester

must supply a voltage of 200 x 0.02 or 4 V to drive the current through

the circuit impedance.

lWith certain additional accessory equipment, the tester could also

be used to test double-pole breakers.

2The unit will supply up to 250 A continuously. Currents between

250 and 300 A should be drawn for limited duration only - say an hour when slightly above 250 A down to 20 minutes at 300 A. OFF-time

after operation at these higher currents should be at least one-tenth

the ON-time, and as much as one-half the ON-time at 300 A.

2
For portability, the tester is divided and packaged into three

separable sections or units. The two heavier Generator Units contain

the constant current generating equipment and range selection switch.

These units are designed to mount on a portable hand truck which

will generally remain outside the house in the area of the electrical

service entry during testing. The Control Unit includes the digital

panel indicating meters and the stop-start and current adjust controls.

It is joined by cables to the other two units and is designed to be

carried inside the house to the vicinity of the service entry panel board.

3. SYSTEM OPERATION

The field circuit breaker tester utilizes the 240-V ac input

power from the electric utility company to generate a low voltage ac constant current for testing the calibration of residential circuit

breakers, in situ. Before testing begins, the connection between utility

power and the circuit breakers to be tested is interrupted; the constant

test current is introduced at this juncture. The tester is composed of

several parts which are described in this section. A block diagram of

the system is shown in figure 1 and more detailed schematics in figures 2,

3, and 4.

Figures 5 and 6 show the three portable cabinets which contain

components for generating, controlling, and measuring the constant

current and for measuring circuit breaker characteristics when subjected

to this current. For convenience in describing them, they are labeled

Generator Input Unit (GIU), Generator Output Unit (GOU), and Control Unit

(CU). When in use, two Generator Units are normally mounted side by side

on a portable hand truck (as shown in fig. 7) and located near the power

company electric utility meter. A 4-ft long, 13-conductor cable connects

one unit with the other. The CU, located in the vicinity of the circuit

breaker panel board, is connected to the GOU via a 30-ft long,

13-conductor cable. 3 The two cables are not interchangeable.

The incoming 240-V ac utility supply is shifted from its normal

path (that is, to the service entry panel) in order to supply power for

the Generator Units. This is accomplished by pulling the electricity

meter and substituting an assembly (fig. 8) which plugs into the same meter socket. The 240-V ac utility input power normally passes

through the upper socket connectors through the electricity meter to

the lower socket connectors and thence to the service entry panel board.

Once the substitute meter assembly has been inserted however, the 240-V ac

( 1 20- V ac each side of neutral) input power passes from the upper socket

connectors into the substitute assembly, through a pair of fast acting

safety fuses and out via a three-wire 15-ft cable to the GIU. The neutral

connection is picked up by a threaded brass rod in the center of the

substitute meter base assembly: this rod is screwed down manually

3The panel board is generally located inside a building as close as possible to the service entrance power usage meter. A 35-ft extension

cable is available if the distance between electric meter and panel board

or the location of building openings through which to pass the cable

necessitate a longer cable length.

3
until it contacts the neutral connection in the power company meter

socket. (If, because of its location, the neutral connection in the

meter socket cannot be contacted by the rod, the tests cannot be

completed without modifying the means of connecting to the neutral.)

This neutral line is carried to the GIU by the third wire in the

cable. The three-wire 15-ft cord from the substitute meter assembly

has a female cord connector on its end which plugs into a motor base

receptacle on the rear of the GIU.

At the GIU the 240-V ac is directed through a ground fault circuit

interrupter (GFCI) and a master control relay, or contactor, to the

primary windings of a motor-driven variable transformer. The 120-V ac developed between one side of the 240-V ac input and the neutral

connection is sent through a second GFCI and used to provide operating

power for the digital panel meters, the autotransformer driving motor,

and other devices within the test equipment. It also furnishes power for

auxiliary lighting, since normal building power is usually cut off when

the electric meter is removed.

Output from the motor-driven variable autotransformer is directed

through 10-A slow blow fuses (replaceable on the front panel) to the

primary winding of a high current transformer located in the GOU. This

transformer has an input-to-output turns ratio of approximately 25, hence

its output voltage is much lower than the input, but its output current is

much higher. The output current, which is the circuit breaker test current,

flows through one or the other of two pairs of instrument transformers

(also located in the GOU): the selection depends on the position of the

large front panel switch on the GOU. This switch (composed of five ganged

double pole, double throw toggle switches) selects the desired output test

current range - either 10 to 100 A or 30 to 300 A. The first instrument

transformer in the chosen path generates a lower level (5 A max.) alternating

current which is proportional to the output test current. This current is

sent back to the regulator controller, located in the GIU. The second

instrument transformer in the test current path generates a similar low level

proportional ac current which is sent to the CU where it is manipulated by a current transducer and various electronic circuits to produce an accurate

indication of the output test current and the length of time during which

it is flowing.

At the regulator controller, the ac current from the first instrument

transformer (proporti onal to the output test current) is converted to a voltage and compared with an internally generated voltage whose value is

set by the position of the current control knob located on the CU front

panel. If the two voltages are not equal, the regulator controller

directs the motor driven autotransformer output to change and cause the

voltages to become equal.

Adjustment of the current control knob to produce a higher test

current causes a rise in the internally generated comparison voltage. To

make the voltages equal again, the regulator controller drives the motor

in a direction to increase the autotransformer output voltage. This causes

an increase in the high current transformer output voltage and, assuming

constant output resistance, an increase in the output circuit breaker

test current.

4
The control loop just described also serves to keep the output test

current constant when changes in output circuit resistance occur. If

output circuit resistance should increase (as it tends to do when current

flow causes wire temperature to rise), the resulting tendency for output

current to decrease is counteracted by the feedback loop which increases

the motor driven autotransformer output sufficiently to maintain the test

current at its preset value. Sensitivity of the feedback loop can be

adjusted by a potentiometer (covered by a screw-on cap) on the regulator

controller. This control should be adjusted to just below the point where

the feedback loop tends to "hunt."

Black and red (or yellow) output connectors, located on the front

panel of the GOU, provide the test current to the line and load sides,

respectively, of the circuit breakers. The black terminal is common to

both ranges of the instrument and is connected by a 15-ft long, high

current, single-conductor cable (AWG #1) to one of the two short cables

hanging from the substitute meter base assembly. Each short cable is

connected to one or the other of the two lower bayonets on the substitute

meter base. These lower bayonets, when inserted into the power company

meter socket, make connection with the panel board bus bars via the

utility service entry cable. The line side of each circuit breaker is

connected to one or the other of these bus bars.

The red (or the yellow) terminal on the GOU is connected to the load

terminal of the circuit breaker to be tested by means of a spring-loaded

probe assembly which is described in more detail below. Connection

between the probe assembly and the GOU is made by a 30-ft long, high

current, flexible, single-conductor cable (AWG #1) routed through the same building opening as the multi conductor cable connecting the CU and

GOU. As with the instrument interconnecting cable, an extension is

available should the cable run be longer than 30 ft.

Test current will not flow unless the switch between the red and

yellow terminals on the GOU is set in the direction of the selected output

terminal. However, internal wiring is designed to prevent damage if the

switch is not correctly set.

The spring-loaded probe assembly (see fig. 9) can be adjusted to

clamp onto the frame of most common panel boards once the cover plate has

been removed. Precise placement of the probe to coincide with the desired

circuit breaker load terminal, as well as adjustment of spring tension,

are accomplished after the assembly has been attached to the panel board.

An additional terminal on the probe facilitates measurement of ac voltage across the circuit breaker while it is undergoing a calibration

test. This voltage, together with the test current value, can be used to

calculate circuit breaker ac resistance.

4C ircuit breaker ac resistance in ohms equals the voltage measured across

the circuit breaker in volts divided by the current flowing through the

breaker in amperes.

5
The GIU and the GOU, which house the constant current generating

equipment just described, are normally located in the area of the service

entry electric meter during a test. Initial turn-on of the equipment and

selection of the test current range must be done at these units. Test

current adjustment, the starting and stopping (if necessary) of a test,

and all voltage, current, and time readings are performed in the vicinity

of the circuit breakers to be tested via the separate, lightweight CU

which is connected to the GOU via a multiconductor cable.

The front panel of the CU includes four digital panel meters, a stop/start control, a current adjust control, an input connector for the

ac voltage measurement, and an indicating light to signal that test current

is flowing. A 120-V ac outlet (7.5 A max.) is also available should it

be necessary to provide additional illumination in the work area. Activation of switches on the GIU, which place the tester in a "stand-by"

condition, is indicated on the CU by the appearance of numbers on the

digital panel meters.

The top panel meter indicates the ac voltage developed across the

circuit breaker during a test (provided the voltmeter leads are connected),

the third one from the top reads the ac test current flowing through the

circuit breaker, and the bottom one reads the time between starting the

test and the end of current flow. The latter indication remains displayed

until the next test has started. The second panel meter from the top

duplicates the peak reading of the test current meter and holds this

reading for a few minutes after the test has been completed. Thus,

confirmation of the test current value is available in those situations

where the circuit breaker opens very quickly.

The ac current and elapsed time indications are both derived from

the output of an instrument transformer located in the GOU. As explained

previously, the circuit breaker test current flows through two instrument

transformers before leaving the GOU. The output of these transformers is an ac current proportional to the circuit breaker test current, but of

lower value (<5 A). The output of the first is part of the constant

current feedback loop as described earlier. The ac current output of the

second instrument transformer is supplied to the CU, where it is converted

to a proportional low level dc current by a current transducer. A change

in circuit breaker test current thus results in a proportional change in

the low level dc current from this transducer.

The actual change in dc current produced for a given change in

circuit breaker test current depends on the output range selected on the

GOU. The instrument transformers each have a 60-to-l turns ratio, but

the one in the path of the 10- to 100-A range has more turns of the

test current conductor through its primary. The instrument transformer

in the path of the 30- to 300-A range has only one turn of the test

current conductor through its primary and thereby produces a 5-A ac output for a 300-A circuit breaker test current (or a 0.05-A output

change for a 3-A test current change). The 5-A ac output is converted

to 1 -mA dc current by the transducer and the 0.05-A change to a 0.01 -mA dc current change. The instrument transformer in the path

6
of the 10- to 100-A output has three turns of the current conductor

through its primary and thereby produces the same 5-A ac output for

only a 100-A test current.

As seen from the above discussion, the additional output range

provides increased resolution at the lower circuit breaker test currents,

i.e., the change in transducer dc output current, which is proportional

to a change in circuit breaker test current, is the same for a 1 -A

test current change when using the 10- to 100-A range as it is for a 3-A test current change when using the 30- to 300-A range.

The front panel ac current indicators are actually dc millivolt

meters which measure the voltage developed across a stable precision

resistor by the proportional dc transducer current. The precision resistor

is switched with the range selected so that the correct scale factor is

maintained, i.e., 1 mA must produce an indication of 100.0 when using the

10- to 100-A range, whereas 1 mA must produce an indication of 300

when using the 30- to 300-A range. 5 The voltage developed across a second resistor in the dc transducer current path is sent to a comparator

circuit which is used to activate the elapsed time indicator.

The elapsed time indicator is a gated electronic counter which counts

the level changes of a derived square wave during the presence of an enabling positive dc input voltage. The period of the square wave is

adjustable by front panel controls so that the count can correspond to

seconds, minutes, or hours. The enabling positive voltage is obtained

from a comparator circuit (see fig. 10) within the CU. If the dc voltage

input to this comparator circuit is above a preset trigger value, the

comparator sends a positive enabling voltage of about 4.6 V to the

counter. The comparator trigger point is adjusted by R3 so that any

circuit breaker test current in excess of approximately 2 A causes

the comparator input to be above its trigger value. Thus, the electronic

counter starts when the circuit breaker test current starts and stops

when the current stops. The counter indication is the time elapsed during

current flow.

The comparator output, which is present only during test current

flow, is also used to activate two solid-state control relays - one within

the GIU and one within the CU. The first is wired in series with the

115-V ac required by the motor which drives the variac. The second is

wired as a "lock-in" for the START switch on the CU. The dc voltage

SThe dc voltmeter used has a range of 0-200.0 mV. For the 10-100-A

output range the resistor value selected is 100 ft so that 1 -mA dc

(corresponding to a 100-A ac test current) will produce a voltage

across the resistor of 100 mV and a 100.0 reading on the meter. For

the 30-300-A test range, the resistor value selected is 30 ft so that 1 -mA dc (correspond!' ng to a 300-A ac test circuit) will produce

a voltage of 30 mV and a 300 reading on the meter. (Connections are available at the rear of the meter for eliminating the decimal point

and are so used in this range.)

7
between 3 and 32 V at the control terminals of these relays activates

the relay and closes any circuit connected to the normally open relay

output terminals.

The purpose of the control relay wired in series with the

autotransformer driving motor is to break the constant current feedback

loop when the circuit breaker under test opens or when the stop button on the CU is operated. This prevents the motor from driving the autotransformer

to maximum output in a futile attempt to keep test current constant.

The purpose of the relay in the CU is to hold the GIU main contactor

closed after the START button is pushed if test current is flowing, and

to release the contactor if current ceases or is not flowing. (As explained

earlier, 240-V ac input to the motor driven variac primary is supplied

through this contactor.) Thus, the contactor will remain closed after

the START button is released only if the test circuit is complete.

Opening of the circuit breaker under test, pushing the STOP switch, or breaking any connection in the current path causes this contactor to open

and thereby remove voltage from the test equipment output terminals.

Also, included in the CU is circuitry to cause resetting of the peakand-hold ammeter approximately 3 seconds after a test is started. This

prevents an abnormally large turn-on transient from being registered and

held by this meter. The reset pulse is obtained from a duo-monostable

multivibrator integrated circuit (see fig. 11) which is activated by the

comparator circuit. When current starts flowing, the comparator output

goes positive and activates the first monostable multivibrator. After a time determined by capacitor C3, the first multivibrator returns to its

original condition. This event activates the second monostable multivibrator

to produce a pulse the length of which is determined by capacitor C4.

This pulse is used to reset the peak-and-hol d meter. The meter may also

be reset manually by pressing the small pushbotton "reset" switch directly

under the CU operating light.

A three-pole, double-throw relay located in the CU chooses the

precision resistor corresponding to the output test current range. This

relay also changes decimal point location on the digital ammeters so it

corresponds to the test current range selected. The relay accomplishes

this by switching certain connections on the rear of the test current

indicating meters. The relay coil is connected to its 120-V ac energizing source by a switch which is ganged with those that select

desired test current range.

Four low voltage dc power supplies are located in the CU, one for

each of the two digital current indicators and two to supply dc voltages

to the comparator and monostable multi vibrator circuits. Each of these

supplies is operated from 120 V ac.

8
4. PREPARATIONS FOR TEST

Some advance planning and a number of setup procedures must be

accomplished before actual testing can begin. This section discusses

those needs. Note that the test procedures are intended to be carried

out by a crew of at least two persons.

Permission to pull the electricity meter at each test site should

always be obtained from the electric utility company. If a number

of test sites are located in a particular area, a prior agreement with

the local utility company may permit a simple notification of test site

and date. The power company may choose to have a representati ve present

during the test. In addition, someone from the company will have to

reseal the electric meter once the tests have been completed.

Utility power will not be restored until the electric meter is

replaced following testing. In some situations, therefore, a portable

generator may be necessary to supply temporary power for heating equipment

or food freezers for the duration of the circuit breaker tests. In such

cases, the auxiliary power must be supplied di rectly to the desired

equipment, not through the circuit breaker panel. This is necessary for

the safety of test personnel and to avoid any possible interference with

the subsequent tests.

The parts necessary to test circuit breakers in the field are given

in table 1. Photographs of the various parts are shown in figures 7, 8,

9, and 12. Operating personnel should be certain that all parts are on hand before proceeding to the test location.

The Control Unit (CU) and most of the necessary cables can be placed

on the hand truck along with the Generator Units (as shown in fig. 13)

while moving the equipment from its storage area to the vehicle used for

travel to the test site. Separation of the units from the hand truck

will generally be necessary before they can be loaded into the transporting

vehicle, however. Weights of various units and interconnecting cables

are given in table 2.

At the test site, the equipment should be unloaded and repositioned

on the hand cart for transport to the actual test location. Precautions

should be taken during transport to avoid moisture or dust contamination

through the ventilation openings of the Generator Units. The hand cart

and Generator Units must be located within 15 ft of the electric meter,

whereas the CU should be placed near the panel board housing the circuit

breakers to be tested. If more than one electric meter is present, it

must be determined which one serves the panel board in question.

The CU is most easily used if placed on the ground or floor with the

front panel facing upwards. The meters are easily read from above in

this position and the wide metal legs keep the unit away from any dirt

and moisture on the floor in the test area.

Once at the test site, the various interconnections between units

can be made. The 4-ft mul ticonductor cable should be connected between

the rear panels of the two Generator Units and the longer (30-ft)

9
mul ti conductor cable connected between the rear panel of the Generator

Output Unit (GOU) and the rear of the CU. The connector pins on the

longer cable can be easily bent, hence the connector should not be forced

into the socket. The guide bar on the bottom and the guide pins on the

exterior of the plug shell should be lined up with their couterparts on the socket and then the connector plug shell gently turned. The cable

should mate easily; if not, the components are not lined up, and forcing

may bend one or more of the connector pins. Following this, one end of

the 30-ft long, high current, single-conductor cable with the red

connectors should be connected into the red or yellow terminal on the GOU

(only one end of this cable will fit into the GOU), and then the range

switch located between the terminals should be set in the direction of

the terminal selected. The other end of the cable should be located near

the CU at the panel board.

The electric meter is typically located outside the building and the

panel board inside (usually in close proximity to the electric meter),

hence the two 30-ft cables must be routed through an opening in the

building, e.g., window, door, etc. Should a convenient opening be lacking

or the panel board be located at some distance from the meter, 35-ft

extensions are provided for each cable to enable total cable runs of as much as 65 ft.

Following the above steps, the connection from the substitute meter

base assembly to the Generator Input Unit (GIU) can be connected. After

checking to be certain that both front panel switches of the GIU are in

the OFF (down) position, the longer cable coming from the substitute

meter base assembly can be inserted into its mating, three-terminal motor

base receptacle on the rear panel of the GIU.

The next step is to prepare for pulling the utility company electric

meter and inserting the substitute meter base assembly. Prior to pulling

the electric meter, any load on branch circuits served from that meter

should be disconnected to eliminate arcing and possible damage to the

contacts when the meter is pulled. Note that the circuit breakers to be

tested must not be opened to remove the load since exercising these

breakers prior to testing may affect the test results. If there are master breakers for the panel, and they are not to be tested themselves,

they should be switched off. Otherwise, all Tights and appliances, etc.,

connected to branch circuits served from the panel board in question

should be turned off. The rotation of the meter disk should be observed

to verify that the loads have been disconnected.

REMOVAL OF THE UTILITY COMPANY ELECTRIC METER SHOULD BE DONE CAREFULLY,

USING THE PROCEDURES APPLICABLE TO THE PARTICULAR METER TYPE. REMOVAL OF

THE METER LEAVES ELECTRICALLY LIVE TERMINALS EXPOSED AT THE METER SOCKET.

DO NOT COME IN CONTACT WITH THESE TERMINALS . The exposed meter socket

should be observed, however, to note whether the socket contacts are spaced to accept the substitute assembly and whether contact can be made

with the power company neutral at the center of the socket. (The neutral

connection needed by the circuit breaker tester is obtained after the

substitute meter assembly has been installed: a threaded brass rod in the

center of the assembly is rotated until it makes contact with the utility

company neutral . Contact between the brass rod and the meter socket case

10
may also be sufficient for obtaining the neutral connection. If the

neutral connection cannot be made with the brass rod, the tests should

be cancelled.)

Before installation of the substitute meter assembly, the threaded

brass rod should be rotated counterclockwise to move it upwards into

the meter base and the assembly positioned so that the wires emerge from

it at the bottom^ Following this the substitute meter assembly can be

inserted into the meter socket and the brass rod rotated clockwise until

it contacts the utility neutral. Connection to the two short cables

coming from the substitute meter assembly or procedure with other steps

must not be made until the correctness of the substitute meter assembly

installation has been verified.

A correct meter assembly installation is verified if the small red

light above the left-hand switch on the GIU lights when that switch is

moved to the ON position. There is no danger in operating this switch

because no voltage is available at any of the instrument output terminals

unless the START button on the CU is depressed and held. Should the

light fail to come on, either (1) the substitute meter may have been

installed incorrectly, (2) the neutral connection may not have been

engaged, or (3) the lamp may have burned out. To determine whether the

neutral has been engaged and the lamp is operable, the right-hand switch

on the GIU should be briefly moved to the ON position and the large white

lamp above that switch observed along with the digital panel meters on the CU. If the large white lamp comes on but the meters don't light up,

then the neutral connection at the meter socket has not been properly

made. If both the lamp and the panel meters light up, then the small red

lamp is probably defective and should be replaced. If neither the lamp

nor the meters light up, then the substitute meter assembly has probably

been installed incorrectly and should be removed immediately.

Once it has been confirmed that the substitute meter assembly has

been installed correctly, both switches on the GIU should be turned off

and the 15-ft long, high current, single-conductor cable with the black

connectors connected between the GOU black terminal and either one of the

two short cables hanging from the substitute meter assembly.

The next step is to select a specific single-pole circuit breaker in

the panel board for test. This requires that the circuit breaker ultimately

be connected between a pair of terminals on the GOU, either the yellow

and black or the red and black.

If proper connections have been made, the line side for one of two

groups of circuit breakers is already connected to the GOU black

terminal. As just described, the black terminal is connected by a high current, single-conductor cable to one of the lower bayonets in the

substitute meter assembly. From there it is connected through the meter

socket to one of the main bus bars in the panel board by means of the

utility company service entry wires. (The other lower bayonet in the

substitute meter base assembly is connected by the same method to the

11
other bus bar in the panel board. )6 The line side of each single-pole

breaker is connected to one or the other of main bus bars depending upon

its location in the panel board. Thus, some circuit breakers have been

connected with the black GOU terminal. Either the red or yellow GOU

terminal must now be connected to the load terminal of the selected

circuit breaker.

Contact with the load terminal of a specific circuit breaker in the

panel board is achieved by means of the probe assembly pictured in

figure 9. FOR INCREASED SAFETY TO OPERATING PERSONNEL, THIS ASSEMBLY

SHOULD BE SET UP AFTER THE UTILITY COMPANY POWER METER HAS BEEN PULLED

AND THE SUBSTITUTE METER ASSEMBLY INSTALLED. (Safety is enhanced since

the utility company's 240 V ac is removed from the panel board when its

meter is removed. Only 11.5 V ac is available from the tester, and even

this is not present until a test is started.)

In most houses, removal of the electricity meter will result in

loss of electric lighting in the panel board area. A 1 20- V ac outlet

(7.5 A max. current) has therefore been installed on the front panel

of the CU for connection of auxiliary lighting. Of course, the substitute

meter assembly must be installed for power to be supplied at the CU.

The circuit breakers to be tested should not be switched nor otherwise

disturbed during the fofl owing setup operation . The panel board cover

plate must be removed to gain access to the circuit breaker terminals and

to provide a surface on which to clamp the probe assembly. The probe

itself is a spri ng-1 oaded brass rod which is positioned, by means of

various clamps, rods, etc., so that its major axis is perpendicular to

the plane of the circuit breaker load terminal (see fig. 14). In the

usual installation, the only accessible portion of the load terminal

(without disturbing any connections) is the head of the screw which clamps

the branch circuit wire to the circuit breaker. Accordingly, the probe

must be positioned to contact that screw head.

After the probe tip has been placed in contact with a surface, spring

tension on the probe can be reduced by turning the white plastic knob at

the rear of the threaded section (see fig. 14) counterclockwise within

the threaded U-shaped metal clamp. Alternatively, the tension can be

eliminated by pulling back on the knurled metal handle surrounding the

wire leading to the probe connector and inserting the dark-colored

"Y-shaped" fork between the white plastic knob and the knurled metal handle

(see fig. 9). This fork should be in place (i.e., eliminating spring

tension) while adjusting the clamping assembly to position the probe

correctly. Spring tension should then be adjusted so that moderate

^Access to both bus bars in the circuit breaker panel cannot be made

with a single connection because the two lower bayonets of the meter

base assembly are purposely not connected together. This was done as

a safety precaution to prevent the extremely hazardous situation that

could otherwise result if the meter base were incorrectly installed

in the inverted position, thereby causing a short circuit across the

incoming 240-V lines.

12
pressure will be placed on the circuit breaker load terminal (screw head)

when the fork is removed. This pressure can be increased later, if

necessary, by rotating the white plastic knob clockwise.

The configuration of the probe clamping assembly can be varied

somewhat in order to conform to the physical characteristics of a given

panel board. Individual probe assembly parts are shown in figure 15,

and their configuration for a typical panel board is depicted in figure 9.

The vise-grip clamps at either end of the assembly are locked onto the

upper and lower edges of the panel board, as shown in figure 16. The

probe itself is attached to a one-half-inch rod which is 26 in. long.

A 48-in. rod is available for use when larger panel boards are encountered.

The real world may present more difficult situations than illustrated

by the mock-up in the photograph. As an example, wires and cables emerging

from the panel board may limit the area available for placing the visegrip clamps. Clamping arrangements within the assembly may have to be

adjusted to compensate for this. In some cases, the edges of the panel

board may have lips which prevent fastening the vise-grip clamps.

Accessory wooden blocks of various thicknesses and shapes will be needed

to fit into the area and provide a clamping surface.

Once the probe clamping assembly is correctly positioned, movement

of the probe to test any circuit breaker in the same vertical column

can be achieved by raising or lowering the U-shaped clamp, which holds

the probe, along the vertical rod. To do this, the spacer fork should be

inserted to remove the probe from contact with the breaker just tested,

the probe clamp thumb screws loosened to permit rotation of the probe

away from the circuit breaker and reposition of it at the next circuit

breaker to be tested, the probe clamp thumb screws re-tightened, and then

the spacer fork removed to bring the probe back into contact with the

(next) screw head.

The high current, single-conductor cable end (red color-coded)

previously left in the vicinity of the CU will eventually be inserted

into the connector at the rear of the probe. This will complete the

connection between the GOU red or yellow terminal and the circuit breaker

load terminal. Refer to the operating procedures for further details.

5. OPERATING PROCEDURES

After the initial setup procedures (as described above) have been

completed, circuit breaker testing can begin. It should be emphasized

here that, even though the maximum tester output voltage of 11.5 V ac

is much less than that thought capable of presenting a shock hazard to

humans, operating personnel should avoid contact with exposed terminals

throughout the testing. Once test current stops flowing, there is no voltage at the output terminals until the START button is pushed again.

(Voltage is available while the START button is being pushed. Voltage

remains after the button is released only if a test current in excess

of 2 A is flowing.) The equipment is configured with both fast-acting

13
fuses and ground fault circuit interrupters to protect operating

personnel in the event of malfunction. Avoiding unnecessary contact

with exposed terminals provides increased assurance of safety for the

operation.

Before a test can begin, the spring-loaded probe assembly (pictured

in fig. 9) must be positioned so that the tip of the probe will be

perpendicular to the plane of the load terminal screw head (see figs. 14 and

16) of the circuit breaker to be tested. (Details of this procedure were provided above.) During initial and all subsequent position adjustments,

the probe tip should be restrained from the test position (i.e., there

should be no contact between probe and circuit breaker) by insertion of

the one-half-inch thick fork-shaped spacer between the knurled metal

probe handle and the white plastic knob used to adjust probe spring

tension (see fig. 9). The probe spring tension should be initially set

at its minimum by rotating the threaded white plastic section counterclockwise

within the metal probe clamp.

After the probe is correctly positioned and before the spacer fork

is removed, the test unit must be preadjusted to deliver the approximate

value of test current desired. This must be done without the circuit

breaker in the current path so that the very large currents which may occur during adjustment will not pass through the circuit breaker.

As a first step in presetting the test current, it must be determined

which panel board bus bar connects to the line terminal of the circuit

breaker to be tested. Contact with this bus bar must be made later in

the preset sequence. If observation and knowledge of panel board

construction are not sufficient to determine this information, a continuity

tester (ohmmeter) may be used. 8 Next, the connections and switches on the

GOU must be set for the desired output current range. For test currents

equal to or less than 100 A, the yellow output connector (10-100 A) should

be used. For currents exceeding 100 A, the red output connector (30-300 A)

must be used. The switch between the yellow and red connectors should be

set in the direction of the output to be used.

Long-term continuous operation at currents exceeding 250 A is not

recommended. However, at 260 A the unit can be operated continuously for

periods up to one hour provided an OFF period of at least one tenth the

7The actual pressure exerted on the circuit breaker load terminal when

the spacer fork is removed will, of course, depend upon how close the

probe tip was to the terminal while the spacer fork was in place. A

prior spacing wider than the fork width will obviously allow no contact

between the probe and the terminal when the fork is removed, while a very small spacing would allow the probe to exert maximum pressure on the terminal. Starting with the probe body rotated counterclockwise

back in its clamp, pressure can be increased substantially if necessary

(e.g., to reduce contact resistance) by turning the white plastic probe

body clockwise within the probe clamp.

80 hmmeter tests will be unambiguous only if all loads are disconnected.

14
ON period is observed. At 300 A operation should be limited to

20-minute periods separated by an OFF time of at least 10 minutes.

In no case should the current exceed 300 A.

The next step is to verify that the switches on the GIU are activated.

Both the auxiliary ac switch and the main ac switch should be placed in

the "up" position. A small red pilot light on the GIU indicates that

auxiliary ac power is available. These switches may be left ON for the

duration of all testing because no current or voltage is present at the

output terminals until the START button on the CU is pushed. Voltage and

current are removed as soon as the circuit is broken (whether the circuit

breaker under test opens, a test wire becomes disconnected, or the STOP

button is pushed).

The range of the digital timer (lower DPM on the control unit) should

be set to correspond to the estimated length of circuit breaker ON time.

If current through the breaker will be less than 150 percent of its rated

current, the thumbwheel switches on the meter face should be set to read

0000600 and the time will be indicated in tenths of a minute up to

99999.9 minutes maximum (approximately 1667 hours or 69 days). If current

through the breaker will be 150 percent or greater of its rated current,

the thumbwheel switches should be set to read 0000010 and the time will be

indicated in tenths of a second up to 99999.9 seconds maximum (approximately

1667 minutes or 27 hours).

Next, the accessory tip (pictured at the right in fig. 12) should be

placed on the end of the red color-coded, high current, single-conductor

cable. The other end of this cable should already be connected to the

G0U red or yellow terminal via passage through a convenient building opening.

This tip is then placed and held in contact with the desired panel board

main bus bar, during which time the CU START button is pushed and held

for one to two seconds before releasing. If all connections have been

made correctly, the ammeters will indicate current flow and the CU current

regulator knob can be adjusted for the desired current^ as read on the

lower ammeter.

If current does not flow when the START button is pushed, the G0U common is probably connected to the opposite panel board bus bar at the

substitute meter base assembly. In this event, the high current, singleconductor cable should be disconnected from the short wire emerging from

the substitute meter base assembly and reconnected to the other short

9The Generator Units have been adjusted for maximum resolution (i.e.,

smallest change of current for a given movement of the control knob)

under normal operating conditions. Should circuit resistance be less

than normal, the unit will tend to "hunt" and sensitivity must be

reduced by means of the sensitivity adjustment on the GIU front panel.

15
wire. 10 The GIU switches do not need to be turned OFF for this operation

provided that the START button on the CU is not operated during the

transfer.

The timer (lower right DPM) will be operating during the preadjustment

period, but its reading may be ignored other than to note whether it is

set for the desired units (seconds or minutes). If it is not, the

thumbwheel switches must be reset.

Once the current has been preadjusted to the desired value, either

the STOP button can be activated for approximately 2 seconds or the

connection to the main bus bar can be removed. The lower ammeter should

now read approximately zero and the timer will indicate the length of

time that the test current was flowing.

After test current preadjustment is complete, the accessory tip can

be removed from the red color-coded cable and the cable inserted into the

connector at the rear of the probe. The probe spacer fork should be

removed with one hand, while the other hand holds the knurled metal handle

to prevent the probe from suddenly lurching forward. The probe should be

allowed to come gently into contact with the circuit breaker load terminal.

If an indication of ac voltage developed across the circuit breaker

while it is undergoing test is desired, the meter connections should be

made at this time. Connections to the top DPM, which indicate ac voltage,

are made through the male microphone latch lock panel connector located

to the right of this meter and above the current adjustment knob. A greycolored, two-wire, shielded cable (the upper center cable of fig. 12)

fits into this connector. The white wire emerging from the other end of

this cable has a small pin on its end which plugs into a small red jack

located at the rear of the threaded white plastic portion of the probe.

10()ne other situation could prevent current flow. It should be investigated

if switching the meter base connectors does not rectify the situation.

If the previous test location required a high-voltage output from the

autotransformer (e.g., to drive the desired test current through a higher

than normal resistance), the output voltage will be at this same high level

when the unit is first activated again. If the present circuit resistance

is low, however, high current will flow until the autotransformer motor has

time to readjust the voltage output to a lower value. During this time the

10-A slow-blow fuses at the bottom of the GIU front panel may blow.

(These fuses have a relatively low rating because they protect the input

to the high current transformer - not its output.) If such is the case,

the fuse should be replaced and resistance added into the test circuit

temporarily. This can be done by using the 35-ft, single-conductor

extension cable. Then the equipment can be activated and the current

adjust control turned counterclockwise. Once the autotransformer has

adjusted downward, the normal procedures can begin again. If the 35-ft

extension is unavailable or does not add sufficient resistance, the

autotransformer can be turned by hand. Remove all power from the equipment

and take off one of the perforated sides’! Rotate the autotransformer arm counterclockwise by placing a finger in one of the holes in the plate

attached to the arm and turn.

16
The black lead has a larger plug on its end which fits into one of two

supplied accessory alligator clips. The appropriate alligator clip is

then attached to the panel board bus bar which feeds the breaker to be

tested.

The voltmeter will indicate to 1.9999 V ac, but as much as 100.0 V ac may be applied without damaging the meter. Resolution of the meter is

0.1 mV.

The circuit breaker test can begin after (1) the test current has

been preadjusted to the desired value, (2) the probe assembly is in place

with the probe contacting the circuit breaker load terminal, and (3) the

ac voltmeter leads have been connected. To start the test, the CU START

button must be pushed and held for approximately 2 seconds. The tester

will shut off automatically when and if the circuit breaker trips, with

time to trip indicated on the timer. This reading will remain until

another test is started or the tester is turned off. For currents no greater than the circuit breaker rating, the breaker should not trip,

hence the test will have to be terminated by pushing the STOP button

after some predetermined length of time.

The second meter from the top on the CU front panel is a peak-and-hol

ammeter. Approximately 4 seconds after a test is started, this meter

resets and thereafter indicates the maximum current flow through the

breaker during that test. This reading is held for a short time after

the test is terminated. This meter is most useful at currents which are 200 percent or more of the circuit breaker rating: at these current

levels, breaker trip time can be quite short and current readings may be

difficult to observe. The peak-and-hol d ammeter provides reassurance that

the circuit breaker test current was at the desired value.

When the test on a circuit breaker has been completed, the spacer

fork should be replaced into the probe assembly to back the probe away

from contact with the circuit breaker load terminal. H Then the probe

clamp thumb screws should be loosened and the probe raised or lowered

along the rod to contact the next circuit breaker to be tested.

6. CONSTRUCTION

The circuit breaker tester is divided into three separable units to

facilitate portability. These units have been designated: (1) Generator

Input Unit (GIU), (2) Generator Output Unit (G0U), and (3) Control Unit (CU).

A schematic diagram for each unit is shown in figures 2, 3, and 4, respectively.

Two subassemblies are located with the CU - the Comparator and the Duo-monostable

multivibrator. Schematics for these subassemblies are shown in figures 10 and 11.

llBecause the circuit breaker tripping mechanism responds to the heat

generated by current flow, consecutive tests should not normally be

conducted on the same circuit breaker. Some "cooling-off" time is

necessary to avoid affecting the results of the next test on that

circuit breaker.

17
A parts list and photographs showing various views of the interior

layout are included for each of the three major units and for the modified

meter base and probe assemblies. Parts for the GIU, GOU, and CU are listed

in tables 3, 4, and 5, respectively.12 Parts for the modified meter base,

the probe assembly, and the interconnecting cables are listed in tables 6

and 7.12 Construction details are shown in the photographs of figures 17

through 26.

12Certain commercial equipment, instruments, or materials are identified

in this paper in order to adequately specify the experimental procedure.

In no case does such identification imply recommendation or endorsement

by the National Bureau of Standards, nor does it imply that the material

or equipment identified is necessarily the best available for the purpose.

18
TABLE 1. Parts Necessary to Test Circuit Breakers In Situ

1 Generator Input Unit

1 Generator Output Unit

1 Control Unit

1 substitute meter base assembly and attached cables

1 hand cart and attached rubber tie-down cords

1 probe assembly including:

1 multiconductor cable - 4 feet long (female cable plugs)

1 multiconductor cable - 30 feet long (female cable plugs)

1 multiconductor cable extension - 35 feet long (one male and one female

cable plug)

1 welding cable - 15 feet long (black connectors)

1 welding cable - 30 feet long (red-coded connectors)

1 welding cable extension - 35 feet long (red-coded connectors)

1 shielded 2 wire cable - 25 feet long (microphone latch lock

connector at one end)

Miscellaneous

1 open end wrench (7/16") for use with probe assembly

1 red-coded adaptor for attachment to red-coded welding cable

2 alligator clip assemblies for attachment to shielded 2 wire cable

1 trouble light

Miscellaneous wooden spacer blocks: 1/2" x 3/4" x 3", 1/2" x 5/8" x 3",

1 probe

1 probe clamp (u shaped)

2 vise grip sheet metal clamps

1 spacer fork

2 long 1/2" rods (26" and 48")

4 short 1/2" rods (8")

2 swivel clamps

2 rod clamps

7 cables

5/8" x 3/4" x 3"

19
TABLE 2. Weight of the Various Field Circuit

Breaker Tester Parts

1 Generator Input Unit 61 lb

1 Generator Output Unit 75 lb

1 Control Unit 14 lb

1 substitute meter base assembly and attached cables 10 lb

1 hand cart (unloaded) 38 lb

1 probe assembly including extra rod 7 lb

2 multiconductor cables (not including extension) 5 lb

2 welding cables (not including extension) 14 lb

All cables (including extensions) 34 lb

Total weight of equipment including cable extensions 239 lb

20
TABLE

3.

Parts

List

for

the

Generator

Input

Unit

(GIU)

21
TABLE

4.

Parts

List

for

the

Generator

Output

Unit

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22
TABLE

5.

Parts

List

for

the

Control

Unit

(CU)

23
TABLE

6.

Parts

List

for

the

Meter

Base

Assembly

and

the

Probe

Assembly

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24
Parts

List

for

the

Interconnecting

Cables

I

25
26
GENERATOR

INPUT

UNIT

go o

QC

27

FIGURE

2.

Schematic

Diagram

of

the

Generator

input

Unit

(GiU)
30 MULTI- CONDUCTOR CABLE

FEMALE CABLE PLUG'

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p—

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1

FIGURE 3. Schematic Diagram of the Generator Output Unit |GOU)

28
e>po<o<2oro

29 i

FIGURE

4.

Schematic

Diagram

of

the

Control

Unit

(CU)
FIGURE 5. Generator Input and Generator Output Units

30
FIGURE 7. Generator Units Mounted on a Portable

Hand Truck

FIGURE 8. Substitute Meter Assembly

31
FIGURE 9. Spring Loaded Probe Assembly

32
+5VDC

OUTPUT TO CONTROL

RELAYS

OUTPUT TO TIMER AND

MULTIVIBRATOR

ALL RESISTORS AND POTENTIOMETERS ARE % WATT

Q1 CAN BE ANY MEDIUM GAIN SILICON NPN TRANSISTOR

R3 SHOULD BE ADJUSTED SO THAT A CIRCUIT BREAKER TEST CURRENT OF 2 TO 3 AMPERES PRODUCES A

HIGH LEVEL (>3.5 Vdc) OUTPUT, AND ZERO TEST CURRENT RESULTS IN A LOW LEVEL (« 1.0 Vdc) OUTPUT

FIGURE 10. Schematic Diagram of the Comparator Circuit

+ 5 VDC

INPUT FROM COMPARATOR

OUTPUT TO PEAK + HOLD AMMETER

RESET

ALL RESISTORS ARE 14 WATT

Q1 CAN BE ANY MEDIUM GAIN SILICON NPN TRANSISTOR Q2 MUST HAVE LOW i EAKAGE CURRENT. USE ANY MEDIUM GAIN SILICON PNP TRANSISTOR

D1 CAN BE ANY GENERAL PURPOSE GERMANIUM DIODE D2 & D3 CAN BE ANY GENERAL PURPOSE SILICON DIODE FIGURE 11. Schematic Diagram of the Duo Monostable Multivibrator Circuit

33
FIGURE 12. Interconnecting Cables (the two extension cables are

not shown)

FIGURE 13. Field Circuit Breaker Tester Prepared for Travel

34
FIGURE 14. Closeup of the Spring Loaded Probe Contacting

a Circuit Breaker Load Terminal

35
FIGURE 15. Individual Probe Assembly Parts

FIGURE 15. Probe Assembly Attached to a Panel Board

36
FIGURE 17. Interior View of the Generator Input Unit

(left side looking toward rear)

37
FIGURE 18. Interior View of the Generator Input Unit

(left side looking toward front)

38
FIGURE 19. Interior View of the Generator Input Unit

(right side looking tcward front)

39
FIGURE 20. Interior View of the Generator Output Unit

(right side looking toward rear)

40
FIGURE 21. Interior View of the Generator Output Unit

(left side looking toward front)

41
FIGURE 22, Side View of the Interior of the Control Unit

42
I

FIGURE 23. Rear View of the Interior of the Control Unit

43
FIGURE 24. Interior View of the Meter Base Assembly

(upper section)

FIGURE 25. Interior View of the Meter Base Assembly

(lower section)

44
FIGURE 26. Rear View of the Meter Base Assembly

45
NBS-1 14A (REV. 2-80

U.S. DEPT. OF COMM. 1. BIBLIOGRAPHIC DATA

SHEET (See instruction s)

PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. NBSIR 81-2301

Publ ication Date May 1982

4. TITLE AND SUBTITLE

FIELD CIRCUIT BREAKER TESTER

5. AUTHOR(S) n ... , -a r , P. Michael Fulcomer

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. TO 80-2

8. Ty pe of Report & Period Covered

: inal

Jan. *80 - Feb. ’81

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State , ZIP)

Consumer Product Safety Commission

Washington, DC 20207

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information . If document includes a significant

bibliography or literature survey , mention it here) Overcurrent protection devices are required within an electrical distribution system to minimize the possibility

of electrically initiated fires caused by circuit overloads.

Circuit breakers are the most commonly used form of overcurrent protection in new and recent residential construction. However,

the complexity of the circuit opening mechanism typical of these

devices makes them susceptible to mechanical deterioration,

which can affect their operation. A circuit breaker so affected

may perform its intended function for a direct short type of fault but may not respond adequately to a less severe circuit

overload condition.

The possibility that an unknown number of installed circuit

breakers might not perform as intended under certain overload

conditions prompted the Consumer Product Safety Commission (CPSC)

to initiate an investigative testing program. The program will

include visiting various field locations, subjecting installed

circuit breakers to controlled overcurrent conditions, and

evaluating their performance. In order to obtain valid field

performance data, the testing will be accomplished without

removing or otherwise disturbing the circuit breakers.

Test equipment developed at NBS for the CPSC to evaluate

the performance of single-pole circuit breakers in residential

installations is described in this report, along with instructions

for its use. The procedures are intended to be carried out by a test crew of at least two persons.

12.

KEY WORDS (Six to twelve entries; alphabet! cal order; capitalize only proper names; and separate key words by semicolons)

circuit breaker; constant current; Consumer Product Safety Commission; electric

power meter; on-site testing; overcurrent protection device; portable; residential

applications; service entry; test.

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