Megger MJ159 Operating Manual

Major MEGGER® Insulation Testers

User Guide

MEGGER

®

Contents

2

Safety Warnings 3

General Description 4

Operation

Testing precautions 5

Preliminary checks 5

Battery condition check (MJ459 and MJ559)5

Battery replacement (MJ459)5

Battery Charging (MJ559)5

Performance checks 6

Voltage measurement 6

Resistance Measurement 6

Insulation testing 7

Using the Guard terminal 7

Fuse Checking and Replacement 8

Specification 9

Accessories 12

Application Notes

Preventive maintenance 13

Insulation Testing Concepts 14

Repair and Warranty 15

Safety Warnings

• Safety Warnings and Testing Precautions must be read and understood before the
instrument is used. They must be observed during use.

• The circuit under test must be switched off, de-energised and isolated before any test
connections are made.

• Test leads, probes and crocodile clips must be in good order, clean and with no broken
or cracked insulation.

• Circuit connections must not be touched during a test.

• Circuits must be discharged before disconnecting the test leads.

• Replacement fuses must be of the correct type and rating.

• When making a voltage measurement, the ‘Test’ button must not be pressed.

• The instrument should not be used if any part of it is damaged.

• U.K. Safety Authorities recommend the use of fused test leads when measuring voltage
on high energy systems.

• Refer to ‘Testing Precautions‘ for further explanations and precautions.

NOTE

THE INSTRUMENTS MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

3

General Description

4

Major Megger MJ159, MJ160, MJ359, MJ459, and
MJ559 testers are compact instruments designed to give

rapid, accurate and direct measurement of continuity and
insulation resistance of domestic and industrial wiring, cables,
transformers, motors, generators electrical machinery and
appliances.

Being self-powered, the instruments are suitable for use
during installation and commissioning work as well as for
service and maintenance applications.

Insulation measuring range is 0,1 Ω to 2000 MΩ (MJ160
0,1 Ω to 1000 MΩ). Automatic discharge for capacitive circuits
under test is provided.

A guard terminal can be used to minimise the effects of
surface leakage when carrying out insulation resistance tests.

In addition each instrument has a 5000Ω Resistance range
making them ideal for testing electrical installations.

Nominal test voltages are 100 V, 250 V, 500 V and 1000 volts
selectable. (MJ160: 50 V, 100 V, 250 V and 500 volts).

All instruments have a mains (line) voltage measuring range
of 0 to 600 V. Although calibrated for a.c voltage, this feature
will give decaying voltage indication following the testing of
equipment possessing capacitance.

The instruments use a moving coil meter with taut band
suspension; white scales on a black scale plate and an
orange ‘dayglow’ needle indicates the resistance value being
measured.
MJ159 and MJ160 are powered by a low voltage, hand
cranked, brushless a.c generator which is connected, after

rectification, to a d.c. to d.c. converter. The generator is
designed to be easy to turn even under full load.

Dual powered units are mains (line) powered with either an
internal hand cranked generator, or battery cells that are re­chargeable by the instrument’s internal charger.

The MJ359 is dual mains (line) or

hand cranked generator

powered.

The MJ559 is dual mains (line) or

rechargeable battery

powered.

Power for the MJ459 is derived from six 1,5 V (IEC LR6)
cells. The cells are connected to a d.c. to d.c. converter to
provide the test voltages.

MJ459 and MJ559 are fitted with a button switch to enable

the battery charge to be checked.

The case is robust, yet light-weight, made from a strong
polycarbonate plastic. Mounted on top of the case is a 5
position, rotary, range selection switch and a ‘Test push
button.

Three shrouded 4 mm terminal sockets marked ‘-’, ’G’ and ’+’
are provided on the side of the case for test lead connection.
Test lead resistance is included in the instrument calibration.
For this reason, only the test leads supplied or replacement
ones should be used.

After the test leads have been connected to the instrument
terminals, the carrying handle folds down neatly over them.
Should the carrying handle accidentally become detached
from the case it may easily be ‘sprung’ back into position.

Operation

TESTING PRECAUTIONS

1. The instruments must only be used by suitably trained
and competent persons.

2. The instruments can give an electric shock. Highly
capacitive circuits (e.g. long lengths of cable) charged to
several kV can create a potentially lethal charge. Circuit
connections must not be touched when testing.

3. Care must be taken to prevent capacitive circuits
becoming disconnected during a test, leaving the circuit
in a charged state.

4. The voltmeter and automatic discharge feature of the
instruments should be regarded as additional safety
features and not

a substitute for normal safe working

practice.

5 Fuse replacements must be of the correct type and

rating. See ‘Specification‘.

6. If any part of the instrument is damaged, it should not be
used, but returned to the manufacturer or an approved
organization for repair.

7. Should the plug on the power cord (MJ359 and
MJ559) not be the type for your receptacles (socket
outlets) do not use an adaptor. Use a suitable alternative
power cord, or if necessary change the plug by cutting
the cord and fitting a suitable plug.

The colour code of the cord is :

U.S.A.

U.K./ International

Ground) Green Yellow/Green
Neutral White Blue
Line Black Brown

If using a fused plug, a 13 Amp fuse to BS1362 should be
fitted.

PRELIMINARY CHECKS

Battery Condition Check (MJ459 & MJ559)

Before initial use of MJ559, charge the battery. To carry out
a battery condition check, press the black battery condition
button (marked ) and confirm that the needle settles within
the portion of the scale marked with the battery symbol. If the
needle settles at less than half scale, the cells must be
replaced (MJ459), or re-charged (MJ559) before
proceeding with any checks or testing.

Battery Replacement (MJ459 only)

The cells are housed in a battery compartment in the base of
the instrument. To change the cells, use a screwdriver to
remove the battery cover securing screw and lift off the
battery compartment cover. Install 6 IEC LR6 cells ensuring
that the polarity is as marked on the base of the battery
compartment. Replace and secure the battery compartment
cover.

Battery Charging (MJ559)

Using the power cord supplied, connect the tester to a
standard a.c. power supply (120 V 50/60 Hz). The red
CHARGE indicator will light to indicate that charging is in
progress. A full charge takes approximately 16 hours. The
MJ559 may be used for testing at the same time as the
battery is being charged.

5

The circuit under test must be completely de-energized
and isolated before test connections are made.