Megger BM11D, BM21 User Manual

5kV Digital Insulation Testers
MEGGER

®

BM11D

MEGGER

®

BM21

User Guide
Guide de l’utilisateur
Gebrauchsanleitung
Guía del usuario

MEGGER

®

Safety Warnings 3
General Description 4
Features and Controls 5 - 6
Operation

Instrument Controls 7 - 8
Features 8
Testing Procedures 9
Battery 9 - 10
Guard Terminal 10 -11
Condition and Warning Indicators 11 -12

Application Notes

Preventive Maintenance 13
Insulation Testing Techniques 14
Short Time or Spot Test 15
Polarization Index (PI) Test 15
Stress Conditions 16

Specification 17 -19

Accessories 20
Repair and Warranty 21
Guide Utilisateur 22 - 37
Betriebsanleitung 38 - 53
Guîa del Usuario 54 - 69

2

Contents

Symbols used on the instrument are:

Caution: Refer to accompanying notes.

Risk of electric shock.
Equipment protected throughout by Double

Insulation (Class

II).

Equipment complies with EU Directives

3

SAFETY WARNINGS

• The circuit under test must be switched off, de-energised and isolated before insulation test connections

are made.

• Circuit connections must not be touched during an insulation test.

• After insulation tests, capacitive circuits must be discharged before disconnecting the test leads.

• Turning the instrument off, and manually discharging of circuits on completion of tests is recommended as
standard procedure, before touching any connections.

• In certain circumstances, break-down of the circuit under test may cause the instrument to terminate the

test in an uncontrolled manner, possibly causing a loss of display while the circuit remains energised. In this
event, it is even more important that the ‘ON/OFF’ key is pressed, and the circuit manually discharged

before touching any connections.

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

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

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

• If water is present in the charger recess, the instrument must not be used. It is recommended that the

instrument is not used in wet weather conditions.

• See Battery Charging Power Cord on page 4.

NOTE

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

The BM11D and BM21 are compact, battery powered, high
voltage d.c. insulation testers with resistance measurement
capabilities to around 1 TΩ. The BM11D has a digital full scale
of 500 GΩ whilst the BM21 can measure up to 5 TΩ. The
BM21 can be set to display leakage current instead of
resistance and this mode of operation also allows higher
resistances to be measured, possibly up to 500 TΩ.

The instruments are microprocessor controlled and feature a
large, clear LCD combining digital and analogue readings of
insulation resistance.

Both instruments have test voltage positions of 500 V, 1000 V,
2500 V and 5000 V. The BM21 has an additional range with a
variable output voltage of 25 V to 5000 V in 25 V steps.

An integral timer is started automatically on commencement of
the test, and displays elapsed minutes and seconds since the
start of the test. The BM21 timer can be used to set the
duration of test, and will automatically stop the output voltage
when the time has expired.

At the end of a test, capacitive loads are discharged
automatically and the decaying voltage is displayed as the
value returns to zero. The test leads should not be
disconnected until the item has been discharged fully. Similarly,
during a test the test leads should not be removed, and the item
under test should not be touched. A flashing LED, and flashing
high voltage symbols on the LCD remind the user that
hazardous voltage is present.

A battery symbol is displayed continuously showing the
condition of the battery.
Power is obtained from internal mains rechargeable batteries.

To recharge the batteries requires an input voltage within the
range 95-265 V a.c., 50-60 Hz. The power input and fuses are
located in a splashproof recess on the front panel.

Battery Charging Power cord:

If the power cord plug is not suitable for your type of socket
outlets (receptacles), do not use an adaptor. You should 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:

Earth (Ground) Yellow/Green
Neutral Blue
Phase (Line) Brown

If using a fused plug, a 3 Amp fuse to BS 1362 should be fitted.
Note: A plug severed from the power cord should be destroyed,

as a plug with bare conductors is hazardous in a live socket
outlet (receptacle).

4

General Description

5

Features and Controls

BM11D Front Panel Layout

12 V Charger Input

Mains Socket

Sliding Cover (open)

Terminal Voltage

Cursor

Cursor

Timer

Selector Keys

On / Off Button

Fuse FS2

Fuse FS1

Warnings

Battery Symbol

Test Button

HV Warning LED

6

BM21 Front Panel Layout

On / Off Button

Sliding Cover (closed)

Terminal Voltage

Battery Symbol

Cursor

Range Keys

Selector Keys

Warnings

Timer

Test Button

HV Warning LED

INSTRUMENT CONTROLS

On/Off Button.

Pressing the On/Off button starts the instrument and initiates a
self check and calibration. All LCD segments appear for 5
seconds, then the word ‘CAL’ appears for about 5 seconds.
When the word ‘CAL’ disappears, the instrument is ready for
use, and is in standby mode. To switch the instrument off, press
the on/off button once. (Auto switch off will occur after 10
minutes of non-use).

Selector Keys

The test voltage is selected by moving the cursor. When the
test button is pressed the instrument will operate at the voltage
indicated.
BM21: In addition to the fixed test voltages the cursor can be
used to select the variable voltage and test duration positions.

Range Keys (BM21 only)

The range keys have two purposes. The first purpose is to
select the measuring range, whether insulation resistance,
leakage current or burn mode. The second function is indicated
by two arrows which appear above the keys when either the
variable voltage or test duration positions are selected. Using
the range keys in this mode will raise and lower the applicable
parameter. The change in voltage is shown at the top of the
display, and the change in test duration is indicated in the
bottom left hand corner of the display.

Test Button

Pressing the large ‘TEST’ button for more than one second will
initiate a test at the selected voltage, simultaneously starting
the timer. Pressing the button again will terminate the test and
connect the internal discharge resistors across the output.
If more than 50 V exists across the terminals, this will be

indicated on the display. If the current flowing into the terminals
exceeds 2 mA it will not be possible to start a test.

A test may be terminated if;

1) The test time is exceeded.

2) The insulation under test suffers a complete breakdown.

3) The battery becomes exhausted.

4) Excessive electrical interference (>2mA at 5 kV) (BM21 only).

Battery Symbol

When the battery is fully charged, all segments of the battery
symbol will be indicated. As the battery is used the segments
will recede. The symbol flashes when the battery capacity is
excessively low (See ‘Battery’).

Cursor

The cursors on either side of the display indicate the ranges
selected.

Condition and Warning Indication

Factors which may affect or inhibit a test are indicated by a
large flashing cursor next to the appropriate warning label.
(See ‘Condition and Warning Indicators‘).

FS1: Mains input fuse.
FS2: Guard fuse.
12 V Charger input

The rechargeable batteries within the instrument can be
charged from a 12 V supply. Connection is made through this
socket. – +

Mains socket

To recharge the internal batteries a mains input of 95-265 V a.c.

7

Operation