• Megger

Megger® BM121 & BM122 Series

Insulation & Continuity Testers

Megger BM121 & 122 Insulation & Continuity Testers


  • Tests insulation at rated voltage into a 1 mA load
  • 200 mA short circuit continuity current
  • Automatic discharge of circuit under test
  • Visual warning of energised circuits above 25 V
  • Designed to International Safety Standards


The Megger® BM120 Series of Digital Insulation and Continuity Testers offers a cost effective solution to testing where only basic test facilities are required. Instruments are available with single insulation test voltages of 500 V d.c. or 1000 V d.c. and test results are displayed on a clear 3-digit autoranging liquid crystal display. Full rated test voltage is produced when supplying up to 1 mA load.

Both instruments offer hands free continuity measurement with a short circuit current of greater than 200 mA and an open circuit voltage of 5 V.

If either instrument is connected to a system which is energised to greater than 25 V, a warning symbol on the display will flash. Under this condition an insulation or continuity test cannot be carried out and the instrument will therefore automatically inhibit any further action until the source of voltage has been removed.

Although insulation tests should only be carried out on de-energised systems, the instruments are protected against accidental connection to phase to earth voltages up to 300 V AC and phase to phase voltages of 440 V AC, Installation Category III.

Further indicators illuminate to show a low battery state and if the protective fuse has ruptured. The instruments will automatically shut down after 5 minutes of non use.

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The BM120 Series will find applications in domestic and industrial electrical contracting and in site maintenance departments.

Both instruments may be used on capacitive circuits since, at the end of an insulation test, the circuit under test will be automatically discharged through 360 k½ internal resistance.

The BM120 Series of Insulation and Continuity Testers are ideal for testing transformers, motors, generators, switchgear, domestic appliances, power tools etc. as well as fixed wiring systems.

Although low cost, both instruments meet the requirements of most International Standards including VDE0413 Part 1, HD384, IEC364 and BS7671 (the 16th Edition of the IEE Wiring Regulations).

This ensures that the rated insulation test voltage can be achieved into a 1 mA load, ie. 500 V into a 500 k½ load or 1000 V into a 1 M½ load.


  • Insulation test ranges produce the rated test voltage into a 1 mA load. Testing can be carried out to International Standards requirements.
  • Single test voltage avoids accidentally overstressing the insulation of the item under test.
  • Clear three digit liquid crystal display produces unambiguous test results.
  • Automatic discharge of capacitive items following an insulation test ensures that circuits are not left dangerously charged.
  • Continuity range has 0,01 ½ resolution and a short circuit current in excess of 200 mA to meet the requirements of International Standards.
  • No need to press the test button when continuity testing leaves both hands free.
  • One button turns instrument on and operates insulation test.
  • Automatic switch-off after 5 minutes.
  • Literature
  • Specifications
Insulation Ranges
BM121 500V
BM122 1000V
Measuring Range:
Digital: 0,01 MΩ to 999 MΩ
Test Current on load:

1mA at minimum pass values
of insulation as specified in
BS7671, HD384, IEC364 and
VDE0413 part 1.

Accuracy (at 20°C): ±3% of reading ±2 digits up to 10 MΩ±5% of reading ±2 digits up to 100 MΩ±30% of reading up to 999 MΩ
Continuity Range:
Measuring Range: 0,01 Ω to 9,99 Ω10,0 Ω to 99,9 Ω
Short Circuit Current: 0,01 Ω to 9,99 Ω 210 mA10,0 Ω to 99,9 Ω 21 mA
Accuracy: 0,01 Ω to 9,99 Ω ±3% ±2 digits10,0 Ω to 99,9 Ω ±5% ±2 digits
Automatic Discharge
When the test button is
released after an insulation
test the item under test will be
automatically discharged
through 360 kΩ internal
Voltage Warning
Symbol flashes on the display and the buzzer sounds
intermittently in the presence of more than 25 VAC, VDC
Auto Shut off
The instrument will automatically switch off after 5 minutes’ inactivity. If the instrument is not to be used for several months,
it is recommended that the batteries be removed from the
Battery Type: 6 X 1,5 V cells IEC LR6 type.
Nickel Cadmium rechargeable
cells may be used.
Battery Life: Typically more
than 2000 tests each of 5
second duration.