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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© 2009, Megger Sweden AB. All rights reserved.
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cy of this document. However, the information contained in this
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a commitment on the part of Megger Sweden AB. Any attached
hardware schematics and technical descriptions, or software
listings that disclose source code, are for informational purposes
only. Reproduction in whole or in part to create working hardware
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Megger Sweden AB.
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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