Page 1
User Manual
MG420
Analog Megohmeter/Insulation Tester
Page 2
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
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 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.
Page 3
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
1. Analog display – See Display Description below
2. Batt Check key – Checks battery level (with
TEST key)
3. 0 ADJ key – Adjusts Zero point for
Analog display
4. Backlight key – Turns on Backlight
5. TEST/LOCK key – Enables Battery
Check, Resistance, and Megohmmeter
functions (can be locked by rotating
clockwise)
6. Function Selector knob – Selects desired
range and function
Page 4
Top View
1. V Test Lead Input
2. COM Test Lead Input
Display Description
1. Red: Megohmmeter Scale: Multiply reading by 0.5 (for 250V
range), 1 (500V), 2 (1000V)
2. Green: Low Resistance Scale (0 to 3 )
3. Green: Resistance Scale (0 to 500
4. Blue: AC Voltage
Measurement Scale (0 to
600V)
5. BATT GOOD Indicator
6. Live Circuit Indicator LED
Page 5
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, especially cables, may retain an
electrical charge when disconnected from the line. It is good practice
to discharge such equipment with grounding straps, or other suitable
devices, before touching or making connections. The meter
automatically discharges the 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 in the test
circuit the red on the meter scale plate will light. Immediately
disconnect test leads and turn off power to 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. Shock to the
user and damage to the meter or device under test can result if testing is
done with voltage present. Proceed with testing only when the voltage is
removed from the device under test.
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.
Page 6
3. Press the Batt Check key.
Range
Reading Multiplier
250V
0.5
500V
1
1000V
2
4. Observe the meter pointer. If the pointer falls in the BATT GOOD
range of the bottom scale, batteries are good. If the pointer falls
outside of (to the left of) the BATT GOOD area, replace the
batteries.
Test Lead Check
1. Set the FUNCTION switch to the 3 range.
2. Touch the test lead tips together and press the TEST key.
3. Resistance should read less than 0.5 .
4. With the leads not touching, the display should read infinity.
5. Readings displayed other than the readings described above are
indicative of a test lead problem. The test leads must be replaced
before using the meter. Failure to do so could result in damage to
equipment and electrical 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
CAUTION: If the LIVE CIRCUIT indicator lights up at this point,
DO NOT operate the TEST key. Remove the test leads and
disconnect all power from the circuit.
1. Press and hold the TEST key to make the measurement. Turn
the key clockwise to lock the test on.
2. Read the value on the MΩ scale and apply the range multiplier
to determine the Megohm resistance reading.
3. Release or unlock the TEST key and allow the device to
discharge before removing the test leads.
Page 7
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 (3 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 (3 or 500
.
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.
Page 8
Battery Replacement
General Specifications
Display
Multiband analog display with
zero adjust
Live Circuit Indicator
LED lights when live circuit is
sensed
Power supply
6 x 1.5V AA batteries
Power consumption
32mA
Fuse Protection
500mA
600V
Operating Temperature
0 to 40oC (32 to 104oF)
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
Specifications
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.
Page 9
Operating Humidity
Below 80%
RH
Altitude
Up to 2000 meters
Storage Temperature
-10 to 60oC (14 to 140oF)
Storage Humidity
Below 70%
RH
Dimensions
200 x 92 x 50mm (7.9 x
3.6 x 2")
Weight
Approx. 700g. (24.7 oz) with
batteries
CAT rating
CATIII 1000V & CATIV
600V
R
RANGES
Range
Resolution
Accuracy
MIN. Open Circuit
Voltage
MIN Circuit
Current
3Ω 0.05Ω
+3%
4.1V
200mA
500Ω 1Ω
4.1V
AC Voltage
Range Res.
Accuracy
Input impedance
Overload
Protect
600VAC
20V
±5%
1.2M
Ω
1000Vrms
Megohmmeter
Specifications
Range
Accuracy
Terminal
voltage
100 Ω 250VDC
0.2M Ω-5M Ω
±5%
250V +
10% ~ -0%
5M to 100 M Ω
±10
%
Page 10
200M 500VDC
0.5M Ω-10M Ω
±5%
500V +
10% ~ -0%
10MM
±10
%
400M 1000VDC
1 M Ω-20M Ω
Ω
±5%
1000V +
10% ~ -0%
20M Ω
±10
%
Range
Test Current
/ Load
Short
circuit
Current
100M 250VDC
250K
1m
A
Approx.
1.3mA 200M 500VDC
500K
400M 1000VDC
1M
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
www.triplett.com
Loading...