Triplett MG420 Analog Megohmmeter/Insulation Tester

Introduction

Congratulations on your purchase of the Triplett MG420 Analog Megohmmeter/Insulation Tester. The MG420 features three Insulation test ranges with a live circuit indicator, as well as low resistance and AC voltage measurements. The Power Lock On feature allows hands-free operation.

Safety

International Safety Symbols

• ⚠️ This symbol, adjacent to another symbol or terminal, indicates the user must refer to the manual for further information.
• ⚠️ This symbol, adjacent to a terminal, indicates that, under normal use, hazardous voltages may be present.
• [Double Insulation] Double insulation.

Safety Notes

• Do not exceed the maximum allowable input range of any function. Set the function switch OFF when the meter is not in use.
• Remove the battery if the meter is to be stored for longer than 60 days.
• Circuits under test must be de-energized and isolated before connections are made (except for voltage measurements).
• Circuit connections must not be touched during a test. Use extreme caution when working near bare conductors and bus bars.
• Accidental contact with conductor could result in electrical shock.
• After insulation tests, capacitors must be discharged.

Warnings

• Set function switch to the appropriate position before measuring.
• When changing ranges, always disconnect the test leads from the circuit under test.

Cautions

• Improper use of this meter can cause damage, shock, injury or death. Read and understand this user manual before operating the meter.
• Always remove the test leads before replacing the battery.
• Inspect the condition of the test leads and the meter itself for any damage before operating the meter. Repair or replace any damage before use.
• Use great care when making measurements if the voltages are greater than 25VAC rms or 35VDC. These voltages are considered a shock hazard.
• Voltage checks on electrical outlets can be difficult and misleading because of the uncertainty of connection to the recessed electrical contacts. Other means should be used to ensure that the terminals are not "live".
• If the equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired.

Description

The Triplett MG420 features several controls and indicators:

1. Analog display: See Display Description below.
2. Batt Check key: Checks battery level (used with the TEST key).
3. 0 ADJ key: Adjusts the zero point for the analog display.
4. Backlight key: Turns on the backlight.
5. TEST/LOCK key: Enables Battery Check, Resistance, and Megohmmeter functions. This key can be locked in the ON position by rotating it clockwise.
6. Function Selector knob: Selects the desired range and function.

The front panel displays the analog meter, various function labels, and the Triplett logo. The CE mark indicates compliance with relevant European directives.

Top View

The top of the meter has input terminals:

1. V Test Lead Input: For the positive (red) test lead.
2. COM Test Lead Input: For the negative (black) test lead.

Display Description

The analog display has multiple scales:

1. Red: Megohmmeter Scale: Readings on this scale must be multiplied by a factor: 0.5 for the 250V range, 1 for the 500V range, and 2 for the 1000V range.
2. Green: Low Resistance Scale: Ranges from 0 to 3.
3. Green: Resistance Scale: Ranges from 0 to 500.
4. Blue: AC Voltage Measurement Scale: Ranges from 0 to 600V.
5. BATT GOOD Indicator: Shows the battery charge status.
6. Live Circuit Indicator LED: Illuminates when a live circuit is detected.

The display also shows labels like "LIVE CIRCUIT", "DO NOT OPERATE", and "BATT GOOD".

Operation

Cautions

• Observe all safety precautions when the FUNCTION switch is set to the 250V, 500V, or 1000V positions.
• Connect the meter test leads to the circuit under test before operating the TEST key.
• Do not touch the clip ends of the test leads when the TEST key is pressed.
• Some electrical equipment may retain an electrical charge when disconnected. Discharge such equipment with grounding straps or other suitable devices before touching or making connections. The meter automatically discharges test circuits when the spring-loaded TEST key is released.

Important Note

• Remove all power to the circuit under test when making resistance measurements. If any voltage is present, the Live Circuit indicator LED will light. Immediately disconnect test leads and turn off power to the test circuit.

Live Circuit Indicator LED

If the Live Indicator status LED is lit, voltage is present on the device under test. DO NOT proceed to test with voltage present, as this can result in shock to the user and damage to the meter or device. Proceed with testing only when the voltage is removed.

Connecting Test Leads

For all measurements, connect the red test lead to the V input terminal and the black test lead to the COM input terminal.

Battery Check

1. Set the range selector switch to the BATT.CHECK position.
2. Press and hold the TEST key.
3. Press the Batt Check key.
4. Observe the meter pointer. If the pointer falls within the BATT GOOD range on the bottom scale, the batteries are good. If it falls outside this area (to the left), replace the batteries.

Test Lead Check

1. Set the FUNCTION switch to the 3Ω range.
2. Touch the test lead tips together and press the TEST key.
3. The resistance should read less than 0.5Ω.
4. With the leads not touching, the display should read infinity.
5. Readings other than these indicate a test lead problem. Replace the test leads before using the meter to avoid damage or shock.

Megohm Measurements

1. Disconnect all power from the circuit to be tested.
2. Connect the red test lead to the V input terminal and the black test lead to the COM input terminal.
3. Set the FUNCTION switch to the desired test range.
4. Connect the test leads to the circuit to be tested.
5. CAUTION: If the LIVE CIRCUIT indicator lights up, DO NOT operate the TEST key. Remove the test leads and disconnect all power from the circuit.
6. Press and hold the TEST key to make the measurement. Turn the key clockwise to lock the test on.
7. Read the value on the MΩ scale and apply the range multiplier to determine the Megohm resistance reading.
8. Release or unlock the TEST key and allow the device to discharge before removing the test leads.

Range Multipliers for Megohm Measurements:

Resistance Measurements

WARNING: Do not run this test unless the voltage on the device under test is zero. If the Live Circuit status LED lights when a test is initiated, immediately abort the test and check that the circuit under test is not powered.

1. Set the Function select switch to the appropriate Resistance (3Ω or 500Ω) position.
2. Connect the red test lead to the V input and the black lead to the COM input.
3. Perform a zero adjustment using the 0 ADJ screw on the unit as described below.
4. Connect the test lead tips to the circuit under test.
5. Press the TEST key. Lock by rotating clockwise if desired.
6. Read the resistance on the appropriate green display scale (3Ω or 500Ω).
7. Release or unlock the Test key.

Zero Adjust

1. Set the range selector switch to the 3Ω or 500Ω range.
2. Short the test leads together.
3. Press the TEST key. Lock by rotating clockwise if desired.
4. Use the 0 ADJ control to align the display pointer with the 0 point on the 3Ω or 500Ω scale.
5. Release or unlock the Test key.

AC Voltage Measurements

1. Set the Rotary switch to the OFF/VAC position.
2. Connect the red test lead to the V input and the black lead to the COM input.
3. Connect the other end of the test leads to the circuit under test.
4. Read the voltage value on the meter.

Battery Replacement

1. If the Battery Check indicates low battery power, the 6 AA batteries must be replaced.
2. Remove the test leads and turn the meter over.
3. Unsnap the tilt stand from the rear of the meter.
4. Remove the 4 Phillips head screws that secure the battery cover.
5. Remove the battery compartment cover.
6. Replace the batteries, observing correct polarity.
7. Replace the battery compartment cover and secure the 4 screws.
8. Re-attach the tilt stand.

♻️ You, as the end user, are legally bound (Battery ordinance) to return all used batteries and accumulators; disposal in the household garbage is prohibited!

You can hand over your used batteries / accumulators at collection points in your community or wherever batteries / accumulators are sold!

Disposal: Follow the valid legal stipulations in respect of the disposal of the device at the end of its lifecycle.

Specifications

General Specifications

RANGES

Resistance Ranges

AC Voltage

Megohmmeter Specifications

Warranty

Triplett / Jewell Instruments extends the following warranty to the original purchaser of these goods for use. Triplett warrants to the original purchaser for use that the products sold by it will be free from defects in workmanship and material for a period of (1) one year from the date of purchase. This warranty does not apply to any of our products which have been repaired or altered by unauthorized persons in any way or purchased from unauthorized distributors so as, in our sole judgment, to injure their stability or reliability, or which have been subject to misuse, abuse, misapplication, negligence, accident or which have had the serial numbers altered, defaced, or removed. Accessories, including batteries are not covered by this warranty.

Copyright © 2021 Triplett