EXTECH 380353

User's Manual
High Voltage Megohmmeter
Analog Insulation Tester
plus AC Voltage and Continuity Tests
Model 380353
EXTECH INSTRUMENTS CORPORATION warrants this instrument to be free of defects in parts and
workmanship for one year from date of shipment (a six month limited warranty applies on sensors and
cables). If it should become necessary to return the instrument for service during or beyond the warranty
period, contact the Customer Service Department at (781) 890-7440 ext. 210 for authorization or visit our
website at www.extech.com (click on ‘Contact Extech’ and go to ‘Service Department’ to request an RA
number). A Return Authorization (RA) number must be issued before any product is returned to Extech. The
sender is responsible for shipping charges, freight, insurance and proper packaging to prevent damage in
transit. This warranty does not apply to defects resulting from action of the user such as misuse, improper
wiring, operation outside of specification, improper maintenance or repair, or unauthorized modification.
Extech specifically disclaims any implied warranties or merchantability or fitness for a specific purpose and
will not be liable for any direct, indirect, incidental or consequential damages. Extech's total liability is limited
to repair or replacement of the product. The warranty set forth above is inclusive and no other warranty,
whether written or oral, is expressed or implied.
Congratulations on your purchase of Extech’s High Voltage Megohmmeter. This meter is
geared toward high voltage insulation testing applications such as appliance testing. In
addition to Megohmmeter (Insulation Resistance) measurements, low resistance and AC
Voltage can be measured. This professional meter, with proper care, will provide years of
safe reliable service.
1. Circuits under test must be de-energized and isolated before connections are made
(except for voltage measurements).
2. 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.
3. Use caution when working near voltages above 60VDC or 30VACrms.
4. After insulation tests, capacitors must be discharged.
5. Test leads (including alligator clips) must be in good working order, clean and without
broken or cracked insulation.
6. When servicing, use only specified replacement parts.
International Safety Symbols
Caution, refer to this manual before using this meter
Dangerous Voltages
Meter is protected throughout by double or reinforced insulation
Rated Environmental Conditions
• Indoor use only
• Installation Category III
• Pollution degree 2
• Altitude up to 2000 meters
• Ambient conditions: Temperature: 32 to 104 F (0 to 40 C); RH: 80% max.
Model 380353 V1.4 02/05
General specifications
Taut band multi-scale analog display with status indicators
and zero adjust
Live circuit indicator
LED lights when live circuit is sensed
Withstand voltage
Meets IEC-1010 safety requirements for Cat. III 600V
Power source
Eight (8) 1.5 AA cells
Power consumption
Megohmmeter: 190mA; Continuity: 120 mA (approx.)
Fuse protection
250V (1A) for Insulation Resistance and Continuity Tests
Operating conditions
32 to 104 F (0 to 40 C); < 80% RH
6.7 x 6.5 x 3.6” (170 x 165 x 92mm)
2.1 lbs (970g)
Low Resistance
Overload Protect.
±5% of reading
0 to 50Ω
Open Circuit V: approx 600mV, Short circuit A: approx. 240mA
AC Voltage
± 5% of full scale
Line Frequency
40Hz to 1kHz
Insulation Resistance / Megohmmeter
Voltage (±10%)
0 to 50MΩ
± 5% of reading
0 to 100MΩ
0 to 400MΩ
Short circuit current: 2mA, Overload Protection: 250V
Model 380353 V1.4 02/05
Meter Description
1. Analog Display
2. Live Circuit status LED
3. Pointer zero adjustment
4. Power Test status LED
5. TEST pushbutton with
Lock function
6. Function select switch
7. Battery/Fuse
compartment on rear
8. Test lead EARTH input
9. Test lead LINE input
10. Test lead storage
Analog Scale Description
1. Black: Megohmmeter Scale: Multiply reading by 0.5 (for 250V range), 1 (500V), 2
2. Red: AC Voltage Measurement Scale (0 to 600V
3. Green: Low Resistance Scale (0 to 50Ω)
Model 380353 V1.4 02/05
Observe all safety precautions when the FUNCTION switch is set to either the 100MΩ
(500V) or the 400MΩ (1000V) position.
Connect the meter test leads to the circuit under test before operating the TEST switch.
Do not touch the clip ends of the test leads when the TEST switch 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
switch is released.
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.
Function switch
The FUNCTION switch is a five position rotary switch and is used to select the desired
range or function.
Test switch
The TEST switch is normally OFF. It is a spring loaded, momentary action for safety. The
test voltage generated by the meter is automatically discharged when the TEST switch is
Connecting Test Leads
For all functions connect the red test lead to the LINE terminal and the black lead to the
EARTH terminal.
Test Lead Check
Set the rotary switch to the low resistance position (Ω). Connect the leads to the meter and
short the clip ends of the test leads and read the green resistance scale on the display.
Depress the TEST switch and the resistance should read between 0 and 0.5 Ω. The
display should read maximum range with the leads open (not shorted). If any readings are
obtained other than the readings just described, the test leads should be considered faulty
and must be replaced before using the meter. Failure to do so could result in damage to
equipment and electrical shock.
Live Circuit Status LED
If the Live Circuit 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.
Power Test Status LED
When the meter is actively testing, the Power Test status LED will blink. When this status
LED is flashing DO NOT touch the test leads or any exposed parts in the testing area.
Hazardous voltages exist that can cause shock. If the Power Test LED fails to light, the
batteries must be replaced. Refer to the Maintenance section near the end of this manual.
Mechanical zero adjust
The pointer should indicate zero on the green 50Ω scale when the FUNCTION switch is in
the Ω position, when the test leads are shorted together, and when the TEST switch is
depressed. If the pointer does not indicate zero, adjust the white plastic mechanical zero
screw located on the lens cover.
Model 380353 V1.4 02/05
Megohm Measurements
Disconnect all power from the circuit to be tested.
Set the FUNCTION switch to the desired test range
Connect the alligator clips to the circuit to be tested
CAUTION: If the LIVE CIRCUIT indicator lights up at this point, DO NOT operate the test
button. Remove the alligator clips and disconnect all power from the circuit.
Press and hold the PRESS TO TEST button to make the measurement. Turn the
button ¼ turn to the right to lock the test on.
Read the value on the MΩ scale and apply the range multiplier to determine the
Megohm resistance reading.
Release the PRESS TO TEST button and allow the device to discharge before
removing the alligator clips.
Reading Multiplier
Low Resistance (Continuity) 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.
Set the Function select switch to the Resistance (Ω) position.
Connect the red test lead to the LINE input and the black lead to the EARTH input.
Perform a zero adjustment using the zero adjust screw on the display as described
Connect the test lead tips to the circuit under test and read the resistance on the
green display scale. The maximum resistance is 50Ω.
The main application for low resistance tests is the identification of low Ω circuits such as
motor runs and start windings which may differ by only a few ohms. With a mid-scale
reading of 2Ω, this test mode can also be used to check relay contact resistance.
AC Voltage Measurements
Set the Function select switch to the red ACV 600V position.
Connect the red test lead to the LINE input and the black test lead to EARTH.
Connect the test lead tips to the circuit under test.
Read the voltage value on the red display scale.
Model 380353 V1.4 02/05
Battery Replacement
If the red Power Test status LED no longer lights when a test is initiated, the eight 1.5 V AA
batteries must be replaced.
1. Ensure that the meter is not in the test mode and that the test leads aren't connected.
2. Remove the Phillips head screw on the rear battery compartment cover.
3. Remove the battery compartment cover.
4. Replace the eight AA batteries ensuring proper polarity.
5. Affix the rear cover and secure the rear screw.
Fuse Replacements
To test for an open fuse first assure that the batteries are not defective and then proceed
as follows:
1. Connect the test leads to the meter and short the clip ends of the test leads.
2. Set the function switch to the ohms position and press the TEST button.
3. If the fuse is open (blown), the pointer will indicate an open circuit (max resistance).
4. To locate the fuse, open the rear battery/fuse compartment via the Phillips head screw
located at the center of the meter case.
5. Replace the fuse (250V, 1A fast blow) located in the battery/fuse compartment just
above and to the right of the batteries. Secure the battery/fuse cover.
Periodically wipe the case with a dry cloth. Do not use solvents or abrasives. Do not allow
water to seep into the meter case.
Calibration and Repair Services
Extech offers complete repair and calibration services for all of the products we sell.
For periodic calibration, NIST certification on most products or repair of any Extech
product, call customer service for details on services available. Extech recommends that
calibration be performed on an annual basis to ensure calibration integrity.
Support Hotline (781) 890-7440
Tech support: Ext. 200; Email: [email protected]
Repair/Returns: Ext. 210; Email: [email protected]
Website: www.extech.com
Copyright © 2005 Extech Instruments Corporation.
All rights reserved including the right of reproduction in whole or in part in any form.
Model 380353 V1.4 02/05