Megger MIT300 User manual

M
MIT300 Series
Insulation and Continuity Testers
USER MANUAL

GSAFETY WARNINGS
nSafety Warnings and Precautions must be read and understood before the instrument is used. They must be observed during use.
nThe circuit under test must be switched off, de-energised and isolated before test connections are made when carrying out insulation and continuity
tests.
nCircuit connections and exposed metalwork of an installation or equipment under test must not be touched.
nThe live circuit warning and automatic discharge are additional safety features which may fail and therefore safe working practices must be
observed.
nThe voltage function will only work if the instrument is functional and switched on.
nAfter insulation tests, capacitive circuits must be allowed to discharge before disconnecting test leads.
nThe instrument should not be used if any part of it is damaged.
nTest leads, probes and crocodile clips must be in good order, clean and with no broken or cracked insulation.
nEnsure that hands remain behind guards of probes/clips when testing.
nNational Safety Authorities may recommend the use of fused test leads when measuring voltage on high-energy systems.
nReplacement fuses must be of the correct type and rating. Failure to fit the correctly rated fuse may result in a safety hazard and may cause damage to
the instrument in the event of an overload.
nThe battery cover must be in place whilst conducting tests.
n The MIT310A is designed for use only in a controlled electromagnetic environment.
2
Users of this equipment and/or their employers are reminded that National Health and Safety Legislation requires them to carry out valid risk assessments of
all electrical work so as to identify potential sources of electrical danger and risk of electrical injury such as inadvertent short circuits. Where the assessments
show that the risk is significant then the use of fused test leads may be appropriate.
NOTE
THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.
CAT II - Measurement category II: Equipment
connected between the electrical outlets and the
user’s equipment.
CAT III- Measurement category III: Equipment
connected between the distribution panel and
the electrical outlets.
CAT IV - Measurement category IV: Equipment
connected between the origin of the low-voltage
mains supply and the distribution panel.

Insulation testing 15
Test lock 15
SP4F Switched (optional accessory for MIT320) 16
Test result storage (MIT330 only) 16
Replacing batteries and fuses 18
Low battery warning symbol 18
To replace batteries 18
Fuse replacement (user replaceable) 19
Preventive maintenance 19
Technical specification 20
Accessories and equipment 23
Repair and Warranty 24
Symbols used on the instrument are:
F Caution: risk of electric shock
G Caution: refer to accompanying notes
t Equipment protected throughout by Double
Insulation (Class II)
c Equipment complies with current EU directives.
Equipment complies with ‘C tick’ requirements
CONTENTS
3
Safety warnings 4
Introduction 2
General description 4
Case contents 5
LCD display 6
Front panel (digital instruments) 6
Connection panel 7
Lid open/closure 7
Preparations for use (all instruments) 8
Batteries 8
Preliminary test lead check 8
General operating instructions 8
General functions 8
Test lead connection. 9
Continuity measurement (MIT300, 310, 320, 330) 10
Test lead null 10
Continuity test (MIT300, 310,320, 330) 10
Continuity Buzzer (MIT300, 310, 320, 300) 11
Continuity buzzer mode: 11
Setup mode (MIT320/330 only) 11
Insulation testing - General 12
Insulation test 12
Test lock 13
Insulation test (MΩ alarm ON/OFF (MIT320 only) 13
MΩ threshold adjustment (MIT320/330 only) 13
Insulation test lock disable (MIT320/330 only) 13
AC / DC Voltage measurement 14
Analogue Instrument MIT310A 14
Test lead null 14
Continuity test 15
Continuity buzzer test 15

The MIT300 series variants have the following features:
MIT300 MIT310 MIT310A MIT320 MIT330
Insulation testing
1 kV Insulation range nnn n
500 V Insulation range nnnn n
250 V Insulation range nnnn n
Insulation test full scale 999 MΩ 999 MΩ 999 MΩ 999 MΩ 999 MΩ
Insulation limit alarm
0.01 MΩ to 1 GΩ n n
Continuity
Voltmeter range
(600 V digit) nnn n
Continuity buzzer nnnn n
Adjustable buzzer
threshold 1 Ω to 20 Ω nn
Audible buzzer disable nn
Lead null to 9.0 Ω
(0.5 Ω for MIT310A) nn0.5Ω nn
Stored test lead null nnnn n
Resistance
10 Ω to 1M Ω resistance
range nn
INTRODUCTION GENERAL DESCRIPTION
4
Thank you for purchasing the Megger Insulation Tester.
For your own safety and to get the maximum benefit from your
instrument, please ensure that you read and understand the following
safety warnings and instructions before attempting to use the
instruments.
This user guide describes the operation and functions of the following:
MIT300 Series of insulation and continuity testers:
MIT300
MIT310
MIT310A
MIT320
MIT330

Please complete the warranty card and return it to Megger Limited as
soon as possible to help us reduce any delays in supporting you, should
the need arise.
Case contents
1 x MIT300 series insulation tester
1 x Red/Black test lead set with clips
8 x AA (LR6) batteries fitted
1 x Warranty card
1 x Certificate of test
1 x Calibration certificate
1 x CD containing user manual
1 x Printed quick start guide
1 x USB lead (MIT330 only)
1 x SP4F switched probe (MIT320 and MIT330 only)
CASE CONTENTS
5
MIT300 MIT310 MIT310A MIT320 MIT330
Features
Locking test button nnnn n
Backlight and rotary
switch illuminations nn
Voltage warning n
Default voltmeter nnn n
Auto-power-down with
defeat nnnn
Switched test probe
connector nn
Switched test probe nn
Results storage n
Downloading n
USB n

6
LCD DISPLAY FRONT PANEL (DIGITAL INSTRUMENTS)
MIT300, 310, 320 and 330
MIT310A
Voltage warning LED
Test Lock LED
Test lead null
Battery check
Battery condition
indication
Moving coil
Analogue
display
indication
Test lead
connections
Insulation test
ranges
LCD Display
Test lock
Measurment
ranges
Analogue
pointer
Battery
condition
indicator
Warning - refer
to user guide
Multi-fuction
analogue
range display
Fuse blown
indicator
Continuity
indicator
Test lock
warning
Infinity
symbol
Lead null
indicator Digital range
Test button &
test lead null
Back light On/Off
(MIT320 & MIT330
only)
Continuity buzzer
and Resistance
range (MIT320 &
MIT300)
Voltage
range
Neck strap
slots
Range knob
Setup menu
(MIT320 & 330)
Front panel cover
(folded under
instrument)

Memory control keys:
STORE: Store initiates the storing of a test result.
LAST/NEXT: Selects the type of location; ie Job, distribution
board, circuit, phase etc.
ESC: Aborts a save at any time.
OK: Final operation to save the result.
sSelects the job, db, circuit number; ie 01,02,03 etc
t
Lid open/closure
1. Open lid by lifting up front panel tab (1).
2. Fold-away underneath instrument (2 & 3) and push into retaining slot
(4).
Connection Panel
MIT300 Series test lead connections
An interlock sliding panel prevents connection of unsafe test lead
configurations. (MIT320/MIT330 only)
MIT330 Additional Controls
7
Warning!
Refer to user
manual
Memory controls
Last
results
recall
Stored
data
download
Last
result
delete
Voltage
measurement
Minimum input
voltage USB download
Lead connection
(330 only)
Red and black test lead
connections
Switch probe Connection
(320 & 300 only)

GENERAL OPERATING INSTRUCTIONS
8
Safety note:
If a voltage greater than 25 V appears on the circuit under test the
instrument will default to a voltage measurement and display the
supply voltage.
On supply voltages over 50 V the instrument will prevent the
test button from performing an insulation test, protecting your
instrument from damage.
General functions
Voltage Testing on High Energy Systems
Use extreme care when using or measuring voltages above 30 V,
particularly in high energy systems. Fused test leads are available as
optional accessories for local situations where increased protection is
required. See accessories section.
Tests lock
The LOCK Lindicates when an INSULATION test range is locked ON.
It is activated by holding down the [TEST] button, and pressing the LOCK
Lbutton.
Note: See analogue section for MIT310A
Warning: Hazardous voltages can exist on the insulation test range all the
time the [TEST] button is locked down.
Voltage warning (MIT300 only)
If a voltage exists on the circuit under test, the instrument will emit a
warning beep.
If a voltage greater than 50 V exists, testing will be automatically
inhibited.
Batteries
The Megger MIT300 series of instruments are supplied with batteries
fitted. When batteries become exhausted, refer to page 18, battery
replacement.
Warning: Do not switch the instrument on with the battery cover
removed.
Preliminary test lead check
Functional verification
1. Before each use of the instrument visually inspect the test leads, prods
and crocodile clips to confirm that their condition is good, with no
damaged or broken insulation.
2. Check continuity of the test leads by firmly shorting the leads together
and read the test lead resistance measurement directly from the display,
which should be less than 1.0 Ω.
Refer to page 10 for operation guide.
3. Supply voltage
Using an approved method, ensure the circuit to be tested has been
fully disconnected from the supply prior to using the instrument.
PREPARATIONS FOR USE (ALL INSTRUMENTS)

Voltage warning (MIT310A only)
If a voltage exists on the circuit under test the voltmeter will indicate this.
However voltages under 50 V will be displayed but may be difficult to read
from the analogue display.
Default voltmeter (MIT310, MIT320 and MIT330)
The default voltmeter automatically operates if a voltage is present across
the test probes of greater than 25 V.
In Volts range the meter operates at greater than 2 V.
If the voltage exceeds 50 V any further testing is inhibited for safety.
The voltage will be displayed.
Backlight operation (MIT320 and MIT330 only)
Both the display and test ranges are backlit. The backlight function can be
selected at any time while the instrument is switched on by pressing the
BACKLIGHT Jbutton.
The backlight function will switch off automatically 20 seconds after the
instrument has finished testing.
Display warning symbols
GRefer to user manual
Any time the warning triangle is displayed the operator should refer to
the user manual for further information.
LRange lock
Displayed at any time the [TEST] button is locked in the on position.
zLead nulled
Indicates that the test lead resistance has been removed from the test
result.
Battery condition indication. Refer to page 18.
fFuse blown indicator, appears when an instrument fuse has failed.
Refer to page 19.
Test lead connection
The Red/Black test lead set should be connected to the appropriate
sockets on the rear of the instrument marked + and – respectively.
Test probes and crocodile clips are supplied for connection to the circuit
under test.
Fused test leads are available as an optional accessory, please refer to
accessories list at the end of this document.
Application
Do NOT connect this instrument to conductors that exceed the rated
voltage with respect to each other or with respect to earth.
This instrument may be connected to CAT III conductors up to 600 V AC,
or CAT IV conductors up to 300V AC.
See the safety warnings for the definition of CAT ratings.
To maintain user safety and ensure accurate measurements, only use the
test leads supplied by Megger Limited.
9

10
4. The display shows the resistance value. (Maximum 99,9 Ω)
5. Disconnect the test probes to terminate the test.
6. On completion of testing switch to the [OFF] position. Alternatively auto
shut off operates after a period of instrument inactivity.
All continuity measurements are AUTO ranging from 0.00 Ω to 100 Ω on
Digital/analogue scale).
The MIT310A has manual range selection to 2 kΩ.
From 0.00 Ω to 10 Ω test current is greater than 200 mA. From 10 Ω to
100 Ω test current is greater than 20 mA. (See page 15 for MIT310A)
Test lead Null
(See page 14 for MIT310A)
Before using the continuity range or buzzer range for the first time, the test
lead resistance should be ‘zeroed out’. This ensures any measurement does
not include the resistance of the test leads.
1. Connect the test leads to the instrument and firmly short both leads
together.
2. Wait for the reading to stabilise and press the [TEST] button.
3. Display of the zconfirms test leads zeroing. The display
should be 0.00 Ω.
Note: Lead zeroing is retained when the instrument is switched off, or auto
shut-off operates.
To remove the ‘lead zero’ press the [TEST] button again.
Continuity test (MIT300, 310,320 and 330)
(See page 15 for MIT310A)
To make a continuity measurement:
1. Turn the instrument ‘On’ by selecting the continuity Ω range.
2. If required, zero test lead resistance, see test lead null (above).
3. Connect the test probes to the isolated circuit under test. The test will
start automatically.
CONTINUITY MEASUREMENT (MIT300, 310, 320, 330)

11
CONTINUITY BUZZER (MIT300, 310, 320, 330)
4. When the display reaches the desired value release the [TEST] button
5. Press the Lbutton to store the value
To select a threshold value above 5.0 Ω
1. Switch the MIT320 or MIT330 to [SETUP]. The display should flash
between CON and 5.00 Ω.
2. Hold the [TEST] button down until the display shows 1.0 Ω.
3. Release the [TEST] button.
4. Press the [TEST] button again. It will commence counting down from
20 Ω.
5 Release the [TEST] button at the desired value.
6. Press the LOCK Lbutton to store the value.
Buzzer ON/OFF (silent buzzer)
To disable the continuity buzzer:
1. Switch the MIT320 or MIT330 to [SETUP]. The display should flash
between CON and 5.00 Ω.
2. Press and release the [TEST] button until the BUZ sign is displayed.
3. Press and hold the [TEST] button to select the OFF option (Press and
hold again to select ON).
4. Press the Lock Lto store the value.
(See page 15 for MIT310A)
Continuity buzzer mode:
The continuity buzzer has a fast check which looks for a resistance greater
than 1.0 MΩ and will buzz when found. If a voltage is detected the
continuity test will stop (the instrument will not be damaged).
The continuity buzzer will then check for a low resistance path less than
5≈ (or as set on the MIT320 and MIT330), and continue to buzz.
To perform a continuity buzzer test:
1. Set the test range knob to the continuity buzzer Zposition
2. Connect the test probes to the isolated circuit under test.
3. A continuous beep note sounds when the test leads make contact
with resistance less than 5 Ω and contact is maintained. (Resistance
greater than 5 Ω is indicated by a short or intermittent beeping).
4. The buzzer visual indicator symbol closes when continuity
is detected.
Setup mode (MIT320 and MIT330 only)
Continuity buzzer threshold adjustable
The adjustable buzzer threshold adjustment allows the operator to set the
maximum resistance at which the buzzer operates.
To adjust:
1. Switch the MIT320/MIT330 to [SETUP]. The display should flash
between CON and 5.00 Ω.
2. Press and hold down the [TEST] button
3. The buzzer threshold resistance is displayed. This will count down from
5 Ω to 1.0 Ω.

(Refer to page 14 for additional MIT310A notes)
Safety note:
Insulation testing is performed at high DC voltages and could be
hazardous if touched. Always observe the safety precautions when
performing an Insulation test, and ensure all necessary health and safety
precautions are observed.
Automatic Discharge: Capacitive circuits are automatically discharged
when the test button is released following an insulation test.
Insulation measurements are performed at either 250 V, 500 V or 1000 V.
Insulation test
The insulation tests apply a known voltage to the circuit under test and
measure the resulting leakage current.
The circuit under test must be completely de-energised and isolated
before test connections are made.
12
To perform an insulation test:
1. Turn the instrument ‘On‘ by selecting the desired 250 V, 500 V or 1000
V [MΩ] range.
2. Connect the test probes to the isolated circuit under test.
3. Press and hold the [TEST] button; allow the display to settle.
The reading will remain displayed for a few seconds after the push
button is released.
4. Release the [TEST] button before removing the test leads (to enable
the instrument to discharge the circuit under test). If the display shows
VOLTS, wait.
5. On completion of testing switch to the ‘OFF’ position. Alternatively
auto shut-off operates after a period of inactivity.
For MIT310A see notes on insulation testing page 15
Note: To prevent accidental application of 1 kV, a warning display will
flash 1000 V prior to the start of the first 1000 V test.
Note: 50Hz noise from the circuit under test below 100 µA or 25 V is
ignored and will not affect test accuracy.
Higher levels of noise will cause the default voltmeter to indicate. Above
50 V (or 200 µA) testing is inhibited.
Test lock
The insulation test can be locked on by pressing the lock Lwhilst
holding down the [TEST] button.
To disable lock press the [TEST or LOCK] button.
INSULATION TESTING - GENERAL

Insulation test MΩ alarm ON/OFF (MIT320/MIT330 only)
The buzzer can be enabled or disabled for working in office environments.
To enable the buzzer:
1. Switch the instrument to [SETUP].
2. Repeatedly press the [TEST] button until the display shows ON/OFF.
3. Press and hold the [TEST] button to select ON.
4. Press the Lbutton to save.
To disable the buzzer:
1. Switch the instrument to [SETUP].
2. Repeatedly press the [TEST] button until the display shows RON/ON.
3. Press and hold the [TEST] button to select OFF.
4. Press the Lbutton to save.
MΩ threshold adjustment (MIT320 and MIT3300 only)
The buzzer threshold adjustment allows the operator to set the resistance
above which the buzzer operates. The instrument will beep so long as the
insulation value measured remains above the threshold value.
The instrument is supplied with the threshold level set to OFF and the
threshold value set to 1.00 MΩ.
To adjust:
1. Switch the instrument to [SETUP]
2. Repeatedly press the [TEST] button until the display shows RES.
3. The initial insulation alarm level is set to 1.00 MΩ.
4. Press and hold down the [TEST] button. The Threshold limit will decrease
from 999 MΩ to 1.0 MΩ.
5. When the display reaches the desired value release the [TEST] button.
6. Press the Lbutton to store the value.
The instrument will now beep every time an insulation test is
performed, and the measured value is greater than the threshold value
set. (only if buzzer is enabled)
Insulation test lock disable (Not MIT310A)
The instrument is shipped with the test lock function enabled. To disable
the test lock function:
1. Ensure the instrument is switched off.
2. Hold down the Lbutton and turn the range knob to MΩ 500 V.
3. Keep the Lbutton depressed for 10 seconds.
4. The instrument shall display OFF to indicate the lock function is
disabled.
This setting is permanently stored.
To re-enable the test lock function, repeat the above process.
13

If a voltage greater than 2 V a.c. or d.c. is present at the terminals the
measured voltage is indicated on the display. If the fuse is blown the
voltmeter will still operate - see note 1.
For normal voltage measurement:
1. Set the range switch to [V]
2. Connect the test leads to the circuit under test.
3. The display will show the voltage across the test leads.
Note: measured voltage should not exceed 600 V phase to earth.
NOTE 1.
When fuse is blown:
MIT300 - MIT330 voltmeter will operate normally when connected to
more than 5 volts.
MIT310A will show approximately 40% of true voltage.
ANALOGUE INSTRUMENT MIT310A
Additional notes:
Battery Level = Exhausted battery
Battery test
Battery condition can be checked by rotating the range knob to the
battery symbol and pressing TEST button. The position of the needle over
the taper symbol will indicate battery condition. Highest charge to the
right.
Note: NiMH or NiCAD rechargeable batteries show a lower charge than
alkaline batteries, and my not give much warning before becoming
exhausted.
Warning: Always perform a battery test prior to using the instrument to
ensure the instrument will function properly.
LED Indicators:
Two led indicators show testing status information for test lock and
voltage detection
Voltage warning:
If a voltage greater than 50 V exists on the circuit under test and the
TEST button is pressed, the RED ‘V’ LED will light and testing will be
automatically inhibited.
Test lead Null (MIT310A only)
Before using the continuity range for the first time, the test lead resistance
should be ‘zeroed out’. This ensures any measurement does not include
the resistance of the test leads.
To null the test leads:
1. Connect the test leads to the instrument and firmly short both leads
together.
14
AC / DC VOLTAGE MEASUREMENT

15
test should be performed with the leads shorted together or the battery
test mode should be selected to ensure the batteries are in good working
condition.
MIT310A Test lock
The [TEST] button can be locked down to allow continuous continuity or
insulation testing.
To enable the TEST LOCK:
1. Press and hold down the [TEST] button. Press the Lbutton
momentarily.
2. The TEST LOCK LED Lshould light.
To remove TEST LOCK:
1. Press the [TEST or LOCK] button.
2. Wait for the reading to stabilise and adjust the lead null knob zuntil
the display pointer indicates 0 Ω.
3. Lead null should be checked periodically and at the start of each
session to ensure ZERO is maintained, or adjusted as necessary.
Note: Lead null can remove up to 0.5 Ω of lead resistance.
Continuity test (MIT310A)
Continuity range extends from 0.00 Ω to 2 kΩ.
Ranges are not auto-ranging. Manual selection of each range is necessary.
Test currents are: 200 mA to 2 Ω, 20 mA to 20 Ω, 2 mA to 200 Ω,
200 µA to 2 kΩ.
To make a continuity measurement:
1. Select the continuity range required.
2. Connect the test leads to the circuit under test.
3. For a single test press and hold down the [TEST] button.
4. Read the resistance from the appropriate range scale.
To increase battery life release it as soon as possible after a test is
complete.
Continuity buzzer test
It is best to lock the test button down: press and hold down the test
button. Press the lock button momentarily.
Insulation testing
Insulation testing is the same as page 13, however the result is only
displayed as long as the [TEST] button is depressed.
Note: If the batteries are exhausted the instrument may not show a
needle movement when testing. We recommend an occasional insulation

Storing contintuity test results:
Results storage has the following structure:
000, 002…255 = Job number
b00, b01, b02 …99
= Distribution board No.
c00, c01, c02…99 = Circuit number
R12, RrN, Rr2, Rr1, R1 & R2 = Circuit type
P1 to P3 = Phase
Job number ( 000, 001…)acts as a work folder, allowing a
set of results to be saved in one folder.
When downloaded, all results with the same job number can be sorted
together, no matter where they occur in the instruments memory.
Distribution board number b01, b02… and circuit reference c00, c01…:
Results can be assigned a specific distribution board number and circuit
reference number prior to storing.
R1,R2, R12, Rr1 etc circuit, type allows a test to be defined as the circuit
type.
P1, P2 …Phase number, each test can be stored under a particular phase,
P1, P2 or P3.
Unique test number, each test result is assigned a unique test number,
from 0 to 1999. This is automatic and cannot be adjusted.
To store a result:
1. Make a continuity measurement as descried earlier and press
STORE.
16
The SP4F switch probe allows the user to start a test by pressing the
[TEST] button on the probe, instead of the instrument. This allows for
complete hands free testing and increases user safety.
To use the SP4F probe:
1. Connect the SP4F probe to the MIT320 or MIT330 using the special 3
pole +ve socket (in place of the RED test lead).
2. Select a suitable insulation test range.
3. Press and hold down the SP4F probe button. The MIT320 or MIT330
will start an insulation test.
4. When the result has settled, release the probe test button.
SP4F SWITCHED (ACCESSORY FOR MIT320/MIT330) TEST RESULT STORAGE (MIT330 only)

Storing insulation test results:
Storing an insulation test result is exactly the same as a continuity test.
However the circuit type options change to L-E, L-L, L-N, N-E
Downloading results to a PC:
1. Connect the tester to the PC using the USB test lead.
2. Set the tester range knob to [Snd].
3. Run Megger Powersuite Professional or Megger Download Manager
on the PC
4. Select the appropriate downloading instrument from the list
5. Select “download from tester”
6. The test data will automatically download its contents to the
PC.
A bar graph shows the status of the download.
Deleting test results
To delete the latest test result:
1. Set the range knob to [dEL]. The display will flash “dEL”
followed by the test number to be deleted.
2. Press the OK button. The last test result will be will be deleted.
WARNING: This operation is not reversible.
To delete all test data:
1. Set the range knob to [dEL]. The display will flash “dEL”.
2. Press the NEXT or LAST key. The display will flash “ALL”.
3. Press the OK button. All the test results will be deleted.
A bar graph shows the progress of the deletion.
17
2. Select job reference number using ↓ keys then press NEXT.
(Hold the key down to scroll quickly through the numbers)
3. Select distribution board number (b01,02 etc) using ↓ keys
then press NEXT
4. Select circuit number (c01,02 etc) using ↓ keys then press NEXT
5. Select the circuit type, R12, RrN, Rr2, Rr1, R2 or R1 by pressing the ↓
keys, then press NEXT.
6. Select the phase using ↓ keys then press NEXT. The screen will
display a unique test number , which is attached to that particular test.
7. Press OK to save the result.
To store a subsequent result:
To save the next test under the same location job number, distribution
board, circuit reference etc:
1. Make another measurement as described earlier and press STORE.
2. The last Job number ** will be displayed. Press OK.
3. The unique test number will be displayed. Press OK and the result is
stored.
Note: The job number, distribution board, circuit and test type can all be
changed before saving a result by selecting the function using the ↓ keys.
To recall the last test result:
1. Set the range knob to RCL
2. The last unique test number is displayed
3. Press OK and the test result will be displayed.
Note: Only the last test result can be recalled to the display.

WARNING: This operation is not reversible. All data will be deleted.
18
Batteries
Battery type: 8 x LR6 (AA), 1.5 V Alkaline, or 8 x 1.2V NiCAD, or 8 x
1.2V NiMH
Fuse type: 500 mA (F) HBC 50 kA 600 V
Fuse blown symbol f
Low battery warning symbol
The battery condition is continuously displayed by the symbol .
When the batteries are exhausted, symbol will show
and testing is inhibited.
Note: Fully charged NiMH or NiCAD rechargeable batteries show a lower
charge than alkaline batteries, and may not give much warning before
becoming exhausted.
To replace batteries
Warning: Do not switch the instrument on with the battery cover
removed.
1. Switch off the instrument and disconnect (the instrument) from any
electrical circuits.
2. The rear cover must not be opened if the test leads are connected.
3. To avoid the possibility of electric shock, do not press the test button
or touch the fuse when changing batteries.
4. To remove the rear cover release the screw at the bottom of the
cover and lift the cover upwards.
5. Remove the dead cells.
6. Refit new batteries observing the correct polarity as marked on the
battery compartment.
7. Replace the cover.
REPLACING BATTERIES AND FUSES

19
Warning: - Incorrect battery cell polarity can cause electrolyte leakage,
resulting in damage to the instrument. If the battery condition indicator
does not show a full charge when battery cells are new, a cell may be
reversed.
Note: Battery cells should not be left in an instrument which may remain
unused for extended periods.
Fuse replacement (user replaceable)
To check fuse, select Ω range.
Short circuit the test leads. If the fuse is good, the display will show approx.
0Ω.
Display of the fuse symbol findicates a ruptured fuse.
The fuse is located behind the rear cover. The rear cover must not be
opened if test leads are connected.
To avoid the possibility of shock, disconnect the battery before touching the
fuse.
A replacement fuse must be of the correct type and rating.
Fuse: 500 mA (F) H.B.C. 50 kA min 600 V (32 mm x 6 mm)
The MIT series instruments require very little maintenance.
Test leads should be checked before use to ensure there is no damage.
Ensure batteries are removed if left unused for extended periods.
When necessary, the instrument can be cleaned with a damp cloth.
Do not use alcohol based cleaners as these may leave a residue.
PREVENTIVE MAINTENANCE

20
Note: For the MIT310A only, the presence of fast transients in excess of
0.5kV or r.f. in excess of 1 volt on measured circuit may affect the results
General Specification
Insulation ranges
Nominal test voltage:
MIT310, 310A, 320, 330 1000 V, 500 V, 250 V (d.c.)
MIT300 500 V, 250 V (d.c.)
Terminal voltage on open circuit (0ºC):
-0% +20% of rated voltage
Measuring Range
All instruments: 10 kΩ - 999 MΩ on all ranges
Short circuit current: 1.5 mA nominal
Test current on load: 1 mA at min. pass values of insulation (as
specified in BS 7671, HD 384 and
IEC 364)
Accuracy (at 20° C)
MIT300, 310, 320, 330: ±3%, ±2 digits up to 10 MΩ, ±5% up to
100 MΩ, ±30% up to full scale
MIT310A: ±2.5% of scale length (or 30% of reading
200 kΩ to 10 MΩ)
Terminal characteristics
Continuity ranges
Measuring range: 0,01 Ω - 100 Ω
(0 -50 Ω on analogue scale)
Open circuit voltage: 5 V ±1 V
Short circuit current: 205 mA +10 mA -5 mA
Accuracy (at 20° C)
MIT300, 310, 320, 330: ±3% ±2 digits
MIT310A: ±2.5% of scale length
(or 30% of reading 0.2 Ω to 2 kΩ)
Measuring range 0 - 2/20/200/2 kΩ
Open circuit voltage 1.5 V +/-0.5 V
Zero offset adjust:
MIT300, 310,320, 330: 0 - 9 Ω
MIT310A: 0 - 0.5 Ω
Continuity buzzer
MIT300, 310: Operates at <5 Ω
MIT320, 330: Adjustable 1 Ω to 20 Ω
MIT310A: Operates at <5 Ω
MIT300, 310, 320, 330: Response time <20 ms
MIT310A: Response time <100 mS
SPECIFICATIONS