Megger MOM200A User manual

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MOM200A/600A
Microohmmeters
ZP-BB04E
User’s Manual

ZP-BB04E MOM200A/600A 3
User’s Manual
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Megger Sweden AB is certified according to ISO 9001 and 14001.
Megger Sweden AB
Eldarvägen 4
Box 2970
SE-187 29 TÄBY
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T [phone]
F [phone]
[e-mail]
www.megger.com
MOM200A/600A
Microohmmeters

4MOM200A/600A ZP-BB04E
Contents
1 Introduction
............................................................. 6
General ..............................................................6
Function description ...........................................6
2 Safety
............................................................. 8
General ..............................................................8
Symbols on the instrument ...................................... 8
Safety instructions ..............................................8
3 Control panels
........................................................... 10
Control panel for MOM200A ...........................10
Control panel for MOM600A ...........................11
4 Operating instructions
........................................................... 12
External measuring instrument............................... 13
Troubleshooting ..................................................... 13
5 Application examples
........................................................... 14
Measuring resistance in a breaker ....................14
Measuring resistance at bus-bar joints ..............15
Expanded measuring range ..............................16
Application example .............................................. 16
6 Specifications
........................................................... 18
Specifications MOM200A ................................18
Specifications MOM600A ................................18

ZP-BB04E MOM200A/600A 5

6MOM200A/600A ZP-BB04E
1 INTRODUCTION
1 Introduction
Function description
Connect the instrument to the object being tested.
After you have adjusted the instrument to provide the
desired current through the test object (100 A for ex-
ample), the actual voltage drop across the test object
will be measured automatically, and all you have to do
is press a button to display the actual resistance.
High current is generated and sent out by the instru-
ment during measurement. A miniature circuit breaker
and a thermal cut-out are provided to make certain
this current doesn’t generate excessive heat inside the
instrument.
The instrument is equipped with a device that guards
against induction. A relay short-circuits the sensing
input when the instrument’s ON/OFF switch is off
and also when the instrument is in the m mode.
To protect against external overvoltages, both the
current output and the sensing input are decoupled to
ground.
MOM200A is used for currents up to 200 A.
MOM600A can provide an output current of up to
600 A, and it can be set to six different measuring
ranges.
Full-wave rectified current is used for measuring.
General
This manual is for the MOM200A, and MOM600A
microohmmeters.
The microohmmeter is designed to measure the
resistances of breaker contacts, bus-bar joints, contact
elements in bus-bars and other high-current links.
When contact resistance rises because of oxidation,
loosened or improperly tightened threaded joints,
temperatures rise abnormally at the points of contact.
This abnormal heating reduces conductivity thereby
accelerating the rise in temperature — and this often
leads to serious trouble.
The microohmmeter can be used to detect such pro-
blems early so that they can be remedied long before
trouble starts. Checking contact resistance at regular
intervals provides a clear indication of the state of
your system.

ZP-BB04E MOM200A/600A 7
1 INTRODUCTION

8MOM200A/600A ZP-BB04E
2 SAFETY
2 Safety
General
Important
Read and comply with the following in-
structions.
Always comply with local safety regula-
tions.
Symbols on the instrument
Caution, refer to accompanying docu-
ments.
Protective conductor terminal.
WEEE, Waste Electrical and Electronic
Equipment. Please utilize your local
WEEE collection facilities in the dispo-
sition of this product and otherwise
observe all applicable requirements.
Safety instructions
Warning
1. Before measuring resistances in circuit breakers
or disconnecting switches (isolators), always
check to see that the object being tested is
closed and grounded on one side.
2. If there is a current transformer in the current
circuit, the protective relay equipment that is
connected to it must be blocked to prevent ac-
tuation. After completing your measurements,
you can follow the normal procedures that are
used to demagnetize current transformer cores
after DC has passed through their current trans-
former.
3. Never open a circuit breaker while a microohm-
meter is connected to it.
4. Current continues to flow for a while after the
microohmmeter is turned off. How long it con-
tinues depends on the ratio of the components
in the L/R circuit.
5. Always connect protective earth (ground).
6. Always use safety connecting leads.
7. Always turn the equipment off before connec-
ting.
8. High voltage/current on input/output terminals.
9. Never leave the instrument unattended while it
is turned on and in the high current mode.
10. Unplug the instrument from the mains supply
when it is left unattended or not in use.
11. Do not attempt to service the instrument your-
self. Opening or removing covers may expose
you to dangerous voltage. If you attempt to
service the instrument yourself the warranty is
no longer valid.
12. Do not use any accessories that are not inten-
ded for use together with the instrument.
13. Disconnect the instrument from the mains
before cleaning. Use a damp cloth for cleaning.
Do not use liquid cleaners or aerosol cleaners.

ZP-BB04E MOM200A/600A 9
2 SAFETY
Important
1. Use only approved mains detachable cable set
with the instrument. Main supply cables shall be
rated for the maximum current for the equip-
ment and the cable shall meet the requirements
of IEC 60227 or IEC 60245. Mains supply cables
certified or approved by a recognized testing au-
thority are regarded as meeting this requirement.
2. Refer all servicing to authorized personnel.
3. If you need to return the instrument, please use

10 MOM200A/600A ZP-BB04E
3 CONTROL PANELS
21 2
4
5
8
6
9
10
7
11
15
14
12
13
16
3 Control panels
Control panel for
MOM200A
1. Positive current output (IOUT+)
2. Sensing terminal (SENSE)
3. Negative current output (IOUT-)
4. Resistance button (R)
5. Current-shunt terminal (SHUNT)
6. Miniature circuit breaker for mains (F1)
7. Miniature circuit breaker for variable trans-
former
8. Grounding terminal
9. ON/OFF switch
10. Mains inlet
11. LED, resistance
12. LED, current
13. LED, thermal cut-out
14. Resistance range switch
15. Current range switch
16. Variable transformer

ZP-BB04E MOM200A/600A 11
3 CONTROL PANELS
21 3
4
5
7
6
8
9
10
11
14
15
12
13
Control panel for
MOM600A
1. Positive current output (IOUT+)
2. Sensing terminal (SENSE)
3. Negative current output (IOUT-)
4. Resistance button (R)
5. Sensing current push buttons
6. Current-shunt terminal (SHUNT)
7. Miniature circuit breaker for mains (F1)
8. Grounding terminal
9. Mains inlet
10. LED, resistance
11. LED, current
12. LED, thermal cut-out
13. Miniature circuit breaker, 17 A
(F3, MOM600 115 V only)
14. ON/OFF switch
15. Variable transformer

12 MOM200A/600A ZP-BB04E
4 OPERATING INSTRUCTIONS
4] Connect the two current cables on two sides
of the test object.
5] Connect the two sensing cables (using the
same polarities as those used for the current
cables) on two sides of the test object and as
close to the test object as possible.
Note The sensing cables must be connected inside
the current cables. Otherwise the test data
may be incorrect. See Fig.1.
Fig. 1
6] Connect the microohmmeter to the mains.
7] Turn on the ON/OFF switch.
8] MOM200A: Select the desired current range
using the "Current range switch".
MOM600A: Select the desired current ran-
ge using the proper "Sensing current push
button".
9] Clear, 0-set, the instrument by turning the
knob (16) on the variable transformer down
to "0", whereupon it will enter the current-
generation mode and LED (12) will light up.
10] Now turn the knob (16) on the variable trans-
former to the right until the current rises to
the desired value. Check the value on the
digital measurement instrument. The analog
instrument (on MOM 600A) provides only an
approximate current reading. To obtain the
best microohm reading, you should try to
generate a current value as close as possible
to the current that you selected with the cur-
rent range switch on MOM200A or the push
buttons on MOM600A.
4 Operating instructions
Important
Read the manual and comply with the
Safety instructions before using the micro-
omhmmeter.
Always comply with local safety regula-
tions.
Note Operating this equipment near sources of
strong electric fields may cause it to display
erroneous current values.
Since power consumption is high, the instru-
ment requires a 16 A fuse.
On the MOM200A model, you must set the
decimal point selector so that the decimal
point is located correctly for the measuring
range. If the display shows an "1" to the far
left the current range has been exceeded
If the thermal cut-out trips (indicated by a
lamp), you must wait until the instrument’s
temperature drops. The thermal cut-out will
then be reset automatically, whereupon the
microohmmeter will be ready to use again.
WARNING
Current continues to flow for a while af-
ter the microohmmeter is turned off. How
long it continues depends on the ratio of
the components in the L/R circuit.
1] Keep the microohmmeter disconnected from
the mains while making connections.
2] Ground one side of the test object.
3] Ground the microohmmeter.

ZP-BB04E MOM200A/600A 13
4 OPERATING INSTRUCTIONS
11] Press resistance button R.
The instrument will interrupt the current
flowing through the test object and enter
the calculation mode. After about two se-
conds, the resistance reading will appear on
the digital display expressed in microohms
(on model MOM600A) or milliohms (on
model MOM200A). The current flowing
through the test object is interrupted auto-
matically, but the reading remains visible on
the display.
12] Turn off and disconnect the microohmmeter
from the mains before doing any disconnec-
tion work or moving any cables or wiring.
External measuring instrument
If, for some reason, you want to use an external
measuring instrument to set the measurement cur-
rent, you can connect it to the current shunt. Voltage
across the current shunt is proportional to the mea-
surement current flowing through the test object,
10 mV per 100 A.
Troubleshooting
Fault Cause Remedy
Display shows
only a 1 at
left.
Current range set on
instrument has been
exceeded.
If possible, select ano-
ther current range.
Expand the current
range using the method
described in section
"Expanded measuring
range".
Poor contact at ends
of sensing cables.
Check the sensing cable
connections.
Thermal
cut-out has
tripped.
Overload. Wait until the tempe-
rature drops and the
light-emitting diode
goes out.
Mains mini-
ature circuit
breaker has
tripped
Overload or fault in
instrument.
Reset the miniature
circuit breaker. If it trips
again, contact service
personnel.

14 MOM200A/600A ZP-BB04E
5 APPLICATION EXAMPLES
Measuring resistance in a
breaker
Important
Read the manual and comply with the
Safety instructions before using the micro-
omhmmeter.
Always comply with local safety regula-
tions.
Fig. 2
1] Make certain the mains are de-energized on
both sides of the breaker. Ground the brea-
ker on one side and make certain it is closed.
2] Keep the microohmmeter disconnected from
the mains while making connections.
3] Ground the microohmmeter.
4] Connect the current cables and the sensing
cables (with the same polarities) on both
sides of the breaker.
Important
The sensing cables must be connected in-
side the current cables. Otherwise the test
data may be incorrect. See fig. 2.
5] Connect the microohmmeter to the mains.
6] Turn on the ON/OFF switch.
7] MOM200A: Select the desired current range
(100 A for example) using the "Current range
switch".
MOM600A: Select the desired current range
(100 A for example) using the proper "Sen-
sing current push button".
8] Clear, 0-set, the instrument by turning the
knob (16) on the variable transformer down
to "0", whereupon it will enter the current-
generation mode and LED (12) will light up.
9] Increase the current as close as possible to
the desired value (100 A in this case, which
was the range you just selected). Set the
current accurately using the digital measu-
ring instrument. If you want to generate
currents that are outside the selected measu-
ring range, you must calculate the resistance
manually as set forth in application example
"Expanded measuring range"(see below).
10] Press resistance button R, whereupon the
instrument will calculate the actual resistance
and present it on the display.
11] Turn off and disconnect the microohmmeter
from the mains before doing any disconnec-
tion work or moving any cables or wiring.
5 Application examples

ZP-BB04E MOM200A/600A 15
5 APPLICATION EXAMPLES
Measuring resistance at
bus-bar joints
Important
Read the manual and comply with the
Safety instructions before using the micro-
omhmmeter.
Always comply with local safety regula-
tions.
Fig. 3
1] Make certain the mains are de-energized and
the test object is grounded.
2] Keep the microohmmeter disconnected from
the mains while making connections.
3] Ground the microohmmeter.
4] Connect the microohmmeter’s current cables
to the test object, see fig. 5. Do not connect
the sensing cables. Measurement will be
done manually using an external portable
voltmeter.
5] Connect the microohmmeter to the mains.
6] Turn on the ON/OFF switch.
7] MOM200A: Select the desired current range
(100 A for example) using the "Current range
switch".
MOM600A: Select the desired current range
(100 A for example) using the proper "Sen-
sing current push button".
8] Clear, 0-set, the instrument by turning the
knob (16) on the variable transformer down
to "0", whereupon it will enter the current-
generation mode and LED (12) will light up.
9] Increase the current as close as possible to
the desired value (100 A in this case, which
was the range you just selected). Set the cur-
rent accurately using the digital measuring
instrument.
10] Using an external voltmeter, measure the
voltage drop (voltage) across each contact
element within every section of the bus-bar
being tested. The multimeter must be set to
DC and to measure voltage. You must calcu-
late the actual resistance yourself.
Example: If the voltage drop is 0.0067 V at
a current of 100 A, the resistance will be
0.0067/100 ohms, i.e. 67 microohms.
11] Turn off and disconnect the microohmmeter
from the mains before doing any disconnec-
tion work or moving any cables or wiring.

16 MOM200A/600A ZP-BB04E
5 APPLICATION EXAMPLES
Expanded measuring range
The measuring range can be expanded by setting
the current lower than what was selected using the
current range switch. Here, you must measure and
calculate the resistance manually, and the accuracy is
somewhat lower than normal. Application example
(see below) illustrates the procedure.
Application example
Important
Read the manual and comply with the
Safety instructions before using the micro-
omhmmeter.
Always comply with local safety regula-
tions.
1] Make certain that the mains are de-ener-
gized and that the test object is grounded.
2] Keep the microohmmeter disconnected from
the mains while making connections.
3] Ground the microohmmeter.
4] Connect the two current cables and two
sensing cables (using the same polarities) to
the two sides measurement site. The sensing
cables must be connected close to the test
object.
5] Connect the microohmmeter to the mains.
6] Turn the instrument’s ON/OFF switch ON.
7] Select the desired current range (400 A for
example) using the sensing current push but-
tons on the MOM600A.
8] Clear, 0-set, the instrument by turning the
knob (16) on the variable transformer down
to "0", whereupon it will enter the current-
generation mode and LED (12) will light up.
9] Increase the current as close as possible to
the desired value (100 A in this case). Set the
current accurately using the digital measu-
ring instrument.
10] Press resistance button R. The instrument will
do the calculation and present an incorrect
resistance reading.
11] To obtain the correct resistance reading you
must multiply the displayed reading by a
factor of X. To obtain X, divide the selected
current range by the generated current.
Example: 400/100 = 4.
Note This procedure expands the microohmmeter’s
measuring range, but the accuracy drops
somewhat.
12] Turn off and disconnect the microohmmeter
from the mains before doing any disconnec-
tion work or moving any cables or wiring.

ZP-BB04E MOM200A/600A 17
5 APPLICATION EXAMPLES

18 MOM200A/600A ZP-BB04E
6 SPECIFICATIONS
6 Specifications
Specifications MOM200A
Specifications are valid at nominal input voltage and an ambi-
ent temperature of +25°C, (77°F). Specifications are subject to
change without notice.
Environment
Application field The instrument is intended for use in
high-voltage substations and indust-
rial environments.
Temperature
Operating 0°C to +50°C (32°F to +122°F)
Storage & transport -40°C to +70°C (-40°F to +158°F)
Humidity 5% – 95% RH, non-condensing
CE-marking
LVD 2006/95/EC
EMC 2004/108/EC
General
Mains voltage 115 / 230 V AC, 50 / 60 Hz
Power consumption 1610 VA (max)
Protection Miniature circuit breakers, thermal
cut-outs
Dimensions
Instrument 280 x 178 x 246 mm (11” x 7” x 9.7”)
Transport case 560 x 260 x 360 mm
(22” x 10.2” x 14.2”)
Weight 14.6 kg (32.2 lbs) 26 kg (54.1 lbs)
with accessories and transport case
Current cables 2 x 5 m (16 ft), 25 mm²
Sensing cables 2 x 5 m (16 ft), 2.5 mm²
Measurement section
Resistance
Range 0 – 1999 µΩ
0 – 19.99 mΩ
Resolution 1 µΩ
10 µΩ
Inaccuracy ±1% of reading + 1 digit
Output
Current 0 – 200 A DC
Open circuit voltage 4.7 V DC
Current shunt output 10 mV / 100 A ±0.5%, max 20 mV
out, max 10 V to protective earth
(ground)
Max. load capacity
Current adjustment set to 100%
Output
current
Min.
output
voltage
Max.
load
time
Rest
time
Input
current at
115 / 230 V AC
100 A DC 3.8 V DC 5 min.
15 min.
15 min.
60 min.
–
200 A DC 3.0 V DC 20 s 5 min. 14 A / 7 A
Specifications MOM600A
Specifications are valid at nominal input voltage and an ambient
temperature of +25°C, (77°F). Specifications are subject to
change without notice.
Environment
Application field The instrument is intended for use in
high-voltage substations and indust-
rial environments
Temperature
Operating 0°C to +50°C (32°F to +122°F)
Storage & transport -40°C to +70°C (-40°F to +158°F)
Humidity 5% – 95% RH, non-condensing
CE-marking
LVD 2006/95/EC
EMC 2004/108/EC
General
Mains voltage 115 / 230 V AC, 50 / 60 Hz
Power consumption (max) 115 V, 4370 VA
230 V, 7360 VA
Protection Miniature circuit breakers, thermal
cut-outs
Dimensions
Instrument 356 x 203 x 241 mm (14” x 8” x
9,5”)
Transport case 610 x 290 x 360 mm
(24.0” x 11.4” x 14.2”)
Weight, 115 V model 25 kg (55.1 lbs)
43.1 kg (95 lbs) with accessories and
transport case
Weight, 230 V model 24.7 kg (54.5 lbs), 42.8 kg (94.4 lbs)
with accessories and transport case
Current cables 2 x 5 m (16 ft), 50 mm²
Sensing cables 2 x 5 m (16 ft), 2.5 mm²
Measurement section
Resistance
Range 0 – 1999 Ω
Resolution 1 μΩ
Inaccuracy ±1% of reading + 1 digit
(at 100 – 600 A test current)
Output, 115 V model
Current 0 – 600 A DC
Open circuit voltage 5.2 V DC
Current shunt output 10 mV / 100 A ±0.5%, max 60 mV
out, max 10 V to protective earth
(ground)
Output, 230 V model
Current 0 – 600 A DC
Open circuit voltage 9 V DC
Current shunt output 10 mV / 100 A ±0.5%, max 60 mV
out, max 10 V to protective earth
(ground)

ZP-BB04E MOM200A/600A 19
6 SPECIFICATIONS
Max. load capacity, 115 V model
Current adjustment set to 100%
Output
current
Min.
output
voltage
Max.
load
time
Rest
time
Input cur-
rent
100 A DC 4.6 V - - 8 A
300 A DC 3.8 V 1.5 min. 15 min. 20 A
600 A DC 2.6 V 10 s 5 min. 38 A
Max. load capacity, 230 V model
Current adjustment set to 100%
Output
current
Min.
output
voltage
Max.
load
time
Rest
time
Input cur-
rent
100 A DC 8.3 V – – 6 A
300 A DC 7.2 V 2.5 min. 15 min. 16 A
600 A DC 5.6 V 15 s 5 min. 32 A

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Subject to change without notice. Printed matter No. ZP-BB04E BB0141IE V01 2010