Megger BMM80 User Manual

M BMM80 Series

Insulation Multimeters

User Guide

SAFETY

WARNINGS

• Safety Warnings and Precautions must be read and

understood before the instrument is used. They

must be

observed during use.

• The circuit under test must be de-energised and isolated
before connections are made except for voltage measurement.

• Circuit connections must not be touched during a test.

• After insulation tests, capacitive circuits must be allowed to

discharge

before disconnecting the test leads.

• The Live Circuit Warning and Automatic Discharge are additional
safety features and

should not be regarded as a substitute for

normal safe working practice.

• Replacement fuses must be of the correct type and rating.
Failure to fit the correctly rated fuse

will result in damage to the

instrument in the event of an overload.

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

• Ensure that hands remain behind guards of probes/clips when
testing.

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

NOTE

THE INSTRUMENTS MUST ONLY BE USED BY

SUITABLY TRAINED AND COMPETENT PERSONS

Users of this equipment and/or their employers are reminded that
Health and Safety Legislation require them to carry out valid risk
assessments of all electrical work so as to identify potential
sources of electrical danger and risk of electrical injury such as
from inadvertent short circuits. Where the assessments show that
the risk is significant then the use of fused test leads constructed
in accordance with the HSE guidance note GS38 ‘Electrical Test
Equipment for use by Electricians’ should be used.

Symbols used on the instruments are:

Caution, risk of electric shock.

Caution, refer to User Guide.

Equipment protected throughout by
Double Insulation (Class II).

Equipment complies with current EU Directives.

Equipment must not be connected
to installations >500V.

>500V

GENERAL DESCRIPTION

The Megger BMM80 Series instruments are battery powered
Insulation and Continuity testers, with a measurement
capability from 0,01Ω Continuity to 200GΩ Insulation.

Offering multi-voltage facilities, the instruments take full
advantage of microprocessor technology and feature a large
liquid crystal display combining digital and analogue readings.
The analogue display has the benefit of indicating trends and
fluctuations in readings, while the digital readout gives direct
accurate results. The display is also backlit giving clear visibility
even in low light conditions.

The BMM80 Series instruments have the unique capability of
being able to measure voltages down to a resolution of 0,1mV.
This gives the user the option to fit a wide variety of
transducers to further enhance the capabilities of the BMM
Series instruments, e.g. temperature or humidity measurement.

There is also a facility to measure capacitance on the BMM80,
this can be used in some types of telecommunications
applications for fault analysis.

A customised connector on the top of the instrument enables
the optional Megger SP6F Switched Probe to be used for two­handed probe operation.

The 250V, 500V and 1000V ranges can be used to test
electrical installations in compliance with BS7671 (16th Edition
IEE Wiring Regulations) IEC364 and HD384, since each range
has a 1mA minimum test current at the minimum pass values
of insulation specified in these documents. The 100V range is
ideal for testing telecommunications equipment which would be
damaged by higher voltages. The 50V range is useful for
testing sensitive equipment, such as electronic components,
and computer peripherals.

Designed to IEC1010-1 the BMM80 Series are protected
against connection to a 500V Category III supply. The
instruments have a basic accuracy of ±2% at 20°C. The
instruments are waterproof and dustproof to IP54. This helps
maintain accuracy and ensures maximum reliability in harsh
environments.

OPERATION

Refer to Safety Warnings before using the instrument

Testing is automatically inhibited if:

• An external voltage >25V is present when
switched to any insulation range position.

• An external voltage >10V is present on all
other ranges (excluding

OFF/V/mV).

The external voltage is indicated on the display, on insulation
ranges an audible bleeper will sound if a test is attempted.

Live Circuit Warning

When more than 25V is applied to the terminals in the insulation
ranges, the instrument defaults to a voltmeter will give an
audible warning if a test is attempted. On all other switch
positions except OFF/v/mV when more than 10V is applied the
default voltmeter will be activated. Testing will be inhibited.

Voltage Testing on High Energy Systems

Use extreme care when using or measuring voltages above
30V, particularly in high energy systems. Fused test leads are
available as optional accessories for local situations where
increased protection is required.

Auto-shut Off

To conserve battery life, Auto-shut Off (preceded by a series of
bleeps) operates after approx. 10 minutes of instrument
inactivity on the insulation ranges, 5 minutes on all other ranges.
If the instrument is switched on whilst holding the key,
the Auto shut-off time is extended to 60 minutes. To restore
operation after Auto-shut Off, either select OFF followed by the
required switch position.

Note: It is recommended that the instrument is switched to the
OFF position when not in use.

Backlight

The backlight is activated by pressing the key. The
backlight will remain illuminated for approximately one minute
before automatically switching off to conserve battery life,
alternatively the key can be re-pressed.

Insulation Tests (MΩ) (See fig.1)

The insulation tests apply a known voltage to the circuit under
test and measure the resulting leakage current. The circuit
under test must be completely de-energised and isolated
before test connections are made.

Insulation tests are only initiated when the TEST button is pressed.

1. Set the range switch to the test voltage required.

2. Connect the test leads, first to the instrument, and then to
the isolated item under test.

3. Press the

TEST button to activate the test voltage. Take

the reading.

4. Release the

TEST button at the end of the test. The last

reading will hold on the display.

5. Any capacitive circuits charged during a test will automatically
discharge. If significant voltage remains the voltage warning
will occur and the voltage present displayed.

6. Remove the test leads only when no voltage is indicated.

Locking Test Button (ltb)

When it is desired to do a long insulation test, the test can be

∼

‘locked on’ by pressing the

key while the TEST

button is held down. The
warning will appear on
the display and both
buttons may be released
whilst the test continues.
The next press of the test
button will terminate the
test.

Note: There is a safety
delay of a few seconds on
the first operation of
‘1000V’ range, each time
the range is selected.

Polarisation Index Testing

Polarisation Index (PI) is the term applied to the Dielectric
Absorption Ratio when resistance values are measured after 1
minute and again after 10 minutes. Polarisation Index is then the
resistance value after 10 minutes divided by the resistance value
after 1 minute. The test can be run at any voltage. More detailed
information on PI Testing and value assessment can be found in
Megger Limited publications listed in the Accessories page.

Automatic Discharge

When the TEST button is released after an insulation test (or
re-pressed if ltb feature is enabled), a 200kΩ load is
automatically switched across the terminals to discharge the
item under test. Any voltage present will be indicated on the
display so that the discharge can be monitored.

TYPICAL TERMINAL VOLTAGE CHARACTERISTICS

Continuity Testing (Ω) (See fig.2)

The continuity tests are activated when the probes make
contact of less than a few kΩ. The tests apply a constant
current and measure the resulting volt drop across the circuit
under test. The test operates without the need to press the
TEST button. When the test leads are removed the reading will
hold for a few seconds and then reset. This range is not
suitable for diode testing since the automatic contact detector

∼

FIG.1