Megger LT310 User manual

M
LT300 Series
Earth Loop Testers
USER MANUAL

GSAFETY WARNINGS
■Safety Warnings and Precautions must be read and understood before the instrument is used. They must be observed during use.
■Continuity of protective conductors and earthed equipotential bonding of new or modified installations must be verified before carrying out an earth
fault loop impedance or RCD tests.
■Do not leave the instrument connected to the mains supply when not in use.
■Circuit connections and exposed metalwork of an installation or equipment under test must not be touched.
■Ensure that hands remain behind guards of probes/clips when testing.
■The instrument should not be used if any part of it is damaged.
■Test leads, probes and crocodile clips must be in good order, clean and with no broken or cracked insulation.
■National Safety Authorities may recommend the use of fused test leads when measuring voltage on high-energy systems.
■The battery cover must be in place whilst conducting tests.
■Voltage indicator LED’s cannot reveal a N-PE supply reversal.
■When making a 2 wire measurement with the 3 wire lead set, for safety reasons the balck test lead should be connected together with the green test lead.
2
Users of this equipment and/or their employers are reminded that 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.
Some national safety authorities recommend fused leads for voltage measurement on high energy systems. If RCD or Loop tests are made it may cause the
fuse to rupture, and so they must be used with caution on voltage testing.
NOTE
THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

Frequency Hz (LT320 and LT330) 16
Phase sequence (LT320 and LT330) 16
Test result storage (LT330 only) 17
Replacing batteries and fuses 18
Low battery warning symbol 18
To replace batteries 18
Fuse blown indication 19
Auto power down 19
Preventive maintenance 20
Technical specification 20
Basic and service errors 22
Accessories and equipment 23
Repair and Warranty 24
Symbols used on the instrument are:
GCaution: refer to accompanying notes
tEquipment protected throughout by Double
Insulation (Class II)
cEquipment complies with current EU directives.
Equipment complies with ‘C tick’ requirements
CONTENTS
3
Safety warnings 3
Introduction 4
General description 5
Case contents 7
LCD display 6
Front panel 6
Connection panel 7
Lid open/closure 7
Preparations for use 8
Batteries 8
Preliminary test lead check 8
General operating instructions 8
Display warning symbols 8
Setup procedure 9
Reverse polarity or line/neutral swapping 9
Test leads 9
Test lead connection. 10
LED indicators 10
Loop testing 11
Non-tripping loop test [No Trip] 11
Hi current loop test [Hi] 11
Phase-Earth loop impedance (not at a power socket): 12
Phase-Neutral or Phase-Phase loop impedance 12
Prospective fault current display [PFC] 12
Error messages 12
Possible sources of error 13
maxZ (LT320 only) 14
Deriving R1 + R2 (LT320 and LT330) 14
Voltage measurement 15
Phase to earth voltage measurement 15
Phase to Phase voltage measurement (LT320 and LT330) 15
N13117

Feature LT310 LT320 LT330
3 Phase safe ■■■
Large clear display ■■■
Backlight ■■
Battery status indication ■■■
Auto power down ■■■
Fuse blown indication ■■■
L-N-E polarity indicators ■ ■ ■
Voltmeter range 500V ■■■
Frequency measurement ■■
Phase rotation indicator ■■
Reverse polarity operation
(some models only) ■■■
Locking test button ■■■
3 wire no trip loop test ■■■
2 wire high loop test ■■■
Phase-Phase loop test ■■
PFC display ■■■
INTRODUCTION GENERAL DESCRIPTION
4
Thank you for purchasing the Megger Earth Loop Impedance 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 manual describes the operation and functions of the following
LT300 series of Loop Impedance Testers:
LT310
LT320
LT330
The LT300 series test instruments have
the following features

Please complete the warranty card and return it to Megger as soon as
possible to help us reduce any delays in supporting you should the need
arise.
Carton contents LT310, LT320 and LT330
1 x LT300 series loop tester
1 x 3 wire test lead with prods with clips
1 x Plug ended test lead
8 x AA (LR6) batteries (fitted in instrument)
1 x Warranty card
1 x Certificate of test
1 x Calibration certificate
1 x CD containing user manual
1 x Quick start guide
1 x Download Manager CD (LT330 only)
CASE CONTENTS
5
Feature LT310 LT320 LT330
Max Zs display ■■
R1+R2/ZRef switch ■■
Plug ended test lead ■■■
3 wire ended test lead
probe/croc clip ended ■■■
Calibration certificate ■■■
IEC61010-1 300V CATIII ■■■
EN61557 ■ ■ ■
Test result storage ■
USB download ■

6
LCD DISPLAY FRONT PANEL

LT300 Series test lead connections
LT320 and LT320
LT310
LT330 additional controls
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.
▲Selects the job, db, circuit number; ie
▼01,02,03 etc
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).
7
Neutral or 2nd
phase connection
USB
connection
(LT330 only)
Single or 3 phase
Single phase connection only
Mains plug test
lead
Maximum 300 V phase
to earth allowed Maximum 300 V phase
to earth allowed
Maximum 500 V across
terminals

PREPARATIONS FOR USE (ALL INSTRUMENTS) GENERAL OPERATING INSTRUCTIONS
8
Tests lock
The LOCK Lindicates when the [Hi] current loop test range is locked
ON.
It is activated by holding down the Llock button, and pressing the
[TEST] button. When activated, the [Hi] current loop resistance
measurement will start when the instrument is connected to a voltage.
The test lock remains on for 30 seconds, after which it resets to off.
Test inhibit
The following conditions may cause the instrument to inhibit testing:
Out of range supply voltage
If an out of range voltage or frequency exists on the circuit under test,
or on a very noisy mains supply, testing will be automatically inhibited.
Overheating
Repetitive loop testing generates heat within the instrument. If this
heat becomes excessive the instrument will warn the operator and
prevent further testing until the instrument has had a chance to cool
down.
Fuse Blown
A fuse blown will prevent the instrument from making further tests.
The fuse indicator will be displayed.
Default voltmeter
The default voltmeter automatically operates in all test modes, indicating
connection to a live system.
Auto power-down
To extend battery life the instrument will automatically switch off six
minutes after the last operation.
The instrument can be switched off manually by selecting [OFF] with the
Batteries
The Megger LT300 series 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
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.

rotary switch, or switched back on again by pressing the [TEST] button.
Backlight operation (LT320 and LT330)
The LT320 and LT330 LCD display may be backlit, to allow readings to be
seen in adverse lighting conditions. 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 15 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.
Battery condition indication. Refer to page 18.
fFuse blown indicator, appears when an instrument fuse has failed.
Refer to page 17.
>280V Displayed on the LT310 indicates a supply voltage in excess of that
allowed is present.
>480V Displayed on the LT320 indicates a supply voltage in excess of that
allowed is present.
hot Indicates the instrument needs to cool down before it can continue
loop testing
Noise on the circuit under test may affect the reading
Setup procedure
Reverse polarity or line/neutral swapping
This feature is only available on the following models
LT310-EN-SC LT320-EN-SC
LT310-FR-SC LT320-FR-SC
LT310-DE-SC LT320-DE-SC
LT310-ES-SC LT320-ES-SC
LT310-IT-SC LT320-IT-SC
LT310-NL-SC LT320-NL-SC
LT310-NO-SC LT320-NO-SC
The set-up menu allows the user to change the way the instrument
behaves when testing on a supply with Line and Neutral connections
swapped. Tests may be permitted or prohibited.
To select Polarity reversal acceptance or rejection:
1. With the instrument switched OFF, hold down the [TEST] button and
turn the range knob to any ON position.
2. Keep the button held down until the instrument displays the ‘SET’
warning.
3. Now release the [TEST] button.
4. Press the [TEST] button again to view the current setting for
line/neutral swapping.
5. The display shows ‘L+L’ (instrument will perform tests with L & N
swapped) or ‘L+N’ (instrument will not perform tests with L & N
swapped).
6. Press the [LOCK] button or the PFC button to change the setting.
7. Press the [TEST] button to exit from the set-up menu.
9

10
Application
This instrument may be connected live to earth or between live conductors
of systems that have a rated voltage of 300V a.c. rms to earth and an
installation (overvoltage) Category III or lower.
This means that the instrument may be connected to any fixed wiring of a
building installation, but not to primary supply circuits such as overhead
cables. To maintain user safety and ensure accurate measurements, only use
the test leads supplied or by Megger Limited.
LED indicators
Three RED led indicators show circuit connection status when correctly
connected to a live circuit. These are for indication purposes only and
should not be relied upon as a indication of the presence of a hazardous
voltage.
Test leads
All test leads form part of the measuring circuit of the instrument and must
not be modified or changed in any way, or be used with any other electrical
instrument or appliance.
The mains plug test lead supplied with the Megger tester is a test lead that
forms part of the measuring circuit of the instrument. The overall length of
this lead must not be altered. If the power cord plug is not suitable for your
type of socket outlets, do not use an adapter. You may change the plug once
only by cutting the cord as close to the plug as possible and fitting a suitable
plug.
The colour code of the cord is:
Earth (Ground) Yellow/Green
Neutral Blue
Phase (Line) Brown
Note: A plug severed from the power cord must be destroyed, as a plug
with bare conductors is hazardous in a live socket outlet.
Test lead connection
The supplied test leads should be connected to the appropriate sockets on
the rear of the instrument marked L0 and L1, or to the 3 way test socket.
Standard test probes and crocodile clips are supplied for connection to the
circuit under test.
The test lead supplied with the LT310, LT320 and LT330 provides connection
for 2 wire testing or 3 wire testing, using the 3 wire (red, black and green)
lead set (6220-782)
all instruments all instruments LT320/LT330

When connected to the circuit to be tested the three status LED’s will
show the following supply connection information:
LED Normal Reversed Notes
indicator supply (L-N) supply
=ON = OFF
L - PE Voltage between L- PE
greater than 25 V
L - N Voltage between L-N
greater than 25 V
N - PE Voltage between N-PE
greater than 25 V
Warning: Voltage indicator LED’s cannot reveal a N-PE supply reversal
Polarity indication
If connected to a single phase power supply by a plug or by the 3-wire
lead set, three LED’s marked L-PE, N-PE and L-N will indicate supply
polarity
Note: The presence of a voltage between phase and earth does not prove
earth continuity, as the earth could have a high resistance and a voltage
would still be measured. To test earth continuity refers to the sections on
loop testing.
LOOP TESTING
11
Two loop testing options are available: [No Trip] and [Hi].
Non-tripping loop test [No Trip]
Earth loop impedance measurement (at a power socket):
The [No Trip] range is a high resolution (0,01 Ω), low test current earth
loop resistance measurement range. It requires a connection to neutral, but
allows quick and accurate measurement of the earth loop resistance
without tripping all RCDs with a rated current 30 mA or higher.
To perform a [No-Trip] loop test:
Range selection:
1. Select the [No Trip] test range. A non-trip loop test is confirmed on the
display with the symbol
2. On the LT320/LT330 set the top rotary knob to [Z]
Testing:
1. Connect the mains plug test lead to the instrument.
2. Insert the plug into an installation socket.
3. Supply voltage is displayed.
4. Press the [TEST] key.
5. After a test period of up to 20 seconds the measured loop value is
displayed.
If desired the test can be repeated by pressing [TEST] again.
Using the three wire lead set
The [No Trip] loop test can be carried out where a power socket is not
available using the three wire lead set.
1. Connect the RED lead to Phase, BLACK lead to neutral and GREEN lead
to earth.

2. Supply voltage is displayed.
3. Press the [TEST] key.
4. After a test period of up to 20 seconds the measured loop value is
displayed.
Hi current loop test [Hi]
The [Hi] Loop test performs a 2-wire loop test, provides a rapid loop test,
designed for non-RCD protected circuits.
NOTE: During all [Hi] tests the BLACK neutral test lead does not need to
be connected, but for safety reasons Megger recommend it is connected
to the same connection point as the GREEN earth test lead.
Range selection:
1. Set the instrument to the [ Hi ] loop test range. A Hi current loop test is
confirmed on the display with the symbol , which indicates the
possibility of tripping an RCD if fitted.
2. On the LT320 and LT330 set the top range knob to [Z].
Phase-Earth loop impedance (not at a power socket)
Testing:
1. Connect the Red/Green lead set or the 3-wire test lead to the
instrument.
2. Connect the RED [L1] lead to PHASE and the GREEN [L0] lead to
EARTH (black lead - connect the black lead to the green lead)
3. The supply voltage is displayed.
4. Press the [TEST] button to start a loop test.
5. After a short delay the measured loop value is displayed.
If desired the test can be repeated by pressing the [TEST] button.
12
Bonded metalwork testing
Repeat the above test but with the green lead connected to the exposed
metalwork.
For a Hi current phase to earth loop impedance measurement at a power
socket, repeat the above test using the mains plug test lead supplied.
Phase-Neutral or Phase-Phase loop impedance
1. Connect the Red/Green lead set or the 3-wire test lead to the
instrument.
2. Connect the RED [L1] lead to PHASE. Connect the GREEN [L0] lead and
the BLACK lead (black lead - ensure the black lead is connected to the
green lead) to NEUTRAL (or the 2nd PHASE for Phase to Phase loop
measurement).
3. The supply voltage is displayed.
4. Press the [TEST] button to start a loop test.
5. After a short delay the measured loop value is displayed. If desired the
test can be repeated by pressing the [TEST] button again.
NOTE: Phase – Phase (415 V) loop test is only possible on the LT320
Prospective fault current display [PFC]
1. On completion of a test, press the [PFC] key.
2. The prospective fault current is displayed in Amps or kA.
NOTES:
The prospective short circuit current (PSCC) of a circuit is the largest
prospective fault current (PFC). In a single phase system, this would be
the larger of the earth loop PFC and the neutral loop PFC. In a multi-phase
system phase-phase loops also need to be considered and these can be
measured using the (Hi) switch position.

The PFC is calculated by using the sum:-
Nominal supply voltage
Loop resistance
The supply voltage used in the calculation depends on the measured
voltage. The instrument uses the following voltage values:-
Actual measured Nominal voltage
voltage
> 50 V and < 80 V 50 V
>80 V and <150 V 110 V
>150 V and <300 V 230 V
>300 V 400 V (LT320 & LT330 only)
PFC measurement accuracy
An accurate PFC measurement requires an accurate measurement of the
loop resistance. The difference of a few digits in the loop resistance
measured will have a large effect on the PFC displayed.
Warning messages
Noise Indication
The symbol is displayed when excessive noise caused by other
equipment exists on the circuit under test. This noise can affect the
accuracy of the loop measurement.
The operator is advised to repeat the measurement or, if the noise symbol
continually appears, investigate the cause.
Voltages greater than 280V [>480V on LT320 and LT330]
LT310: If a voltage greater than 280 V is detected, the display will
show >280 V.
LT320
/LT330: If a voltage greater than 480 V is detected between phases the
display will show >480 V.
Over temperature hot
To protect the instrument from over heating during Loop testing, thermal
protection is fitted. If the message [hot] appears in the display together
with the Gsymbol when loop testing, the instrument must be allowed
to cool down before further attempts are made at loop testing.
Possible sources of error
The reading depends on a measurement of the supply voltage and
therefore noise or transients caused by other equipment during the test
could cause an error in the reading. One way to check for these is to do
two tests and look for any difference in value. The instrument will detect
some sources of noise and warn the user, where other instruments may
give an incorrect reading. Any leakage current as a consequence of other
appliances connected to the supply under test may affect the reading. If
the Phase-Earth loop is being measured, this leakage may be due to filter
capacitors, etc.
Test results may be adversely affected by supply voltage fluctuations or
electrical ‘noise’ during a measurement. It is recommended that tests are
repeated and the results verified, if measurement results are considered
abnormal.
Errors can be reduced by:-
■Use the 2 wire lead set with prods and making a firm connection to
clean conductors.
13
PFC=

14
■Make several tests and taking the average.
■Ensure that potential sources of noise in the installation are isolated
(switched off), eg: automatically switched loads or motor controllers
■Ensuring that the instrument is calibrated.
maxZ (LT320 and LT330)
The maximum loop impedance value of any final ring circuit (or any series
of loop measurements) can be derived by using the [maxZ] function:
To make a [maxZ] measurement:
1. Select the [maxZ] test range
2. Using either the [No Trip] or [Hi] loop tests, make a series of loop test
measurements as described on pages 11 and 12.
3. The display will hold the highest loop measurement, from any number
of loop tests. Lower values are displayed momentarily.
4. Turning the range knob away from [maxZ] removes the maxZ stored
value.
NOTE: maxZ is not stored when the instrument is switched off (or auto-
powers-off), hence auto-power-off time is extended in the Zref and R1+R2
modes to 30 minutes from the standard 6 minutes.
Deriving R1 + R2 (LT320 and LT330)
Automatic Derivation of R1+R2 Values
The LT320 is able to derive the R1+R2 measurement reading from tests
made on a live installation.
NOTE: Care should be taken as any parallel earth paths may effect this
result.
To make use of this feature, the reference/distribution board result must
be stored in the instrument’s memory (Zref), prior to measuring R1 + R2
Saving a Zref (distribution) result
1. Switch the range knob to [Zref].
2. Select a [No Trip] or [Hi] loop test as appropriate.
3. Connect the instrument to the circuit under test as described on pages
11 or 12 as required.
4. Press the [TEST] button to perform a loop test.
IMPORTANT NOTES:
When using Zref and R1+R2 functions, we DO NOT recommend changing
between [No-Trip] or [Hi] test ranges during the test. Always use the same
test method whilst using Zref and R1+R2.
Showing R1+R2
1. After saving a Zref result switch the instrument to R1+R2.
2. All subsequent loop test measurements will have the Zref distribution
resistance subtracted.
3. The Zref value can be updated at any time by returning the Range knob
to Zref and repeating the loop test.
NOTE: Zref is not stored when the instrument is switched off (or auto
powers down), hence auto power-off time is extended in the Z ref and
R1+R2 modes to 30 minutes from the standard 6 minutes.
Application note for Zref and R1+R2 measurement:
On initial verification of a new electrical installation, the value for R1+R2
should be obtained by continuity testing methods (dead testing) as per BS
7671:2001
For periodic inspection reports (PIR) where it is not possible to isolate the
supply, the user should first verify the circuit protective conductor
(standard practice) prior to using the Zref and R1+R2 function on the
Megger LT320 or LT330.

15
VOLTAGE MEASUREMENT
When connected to a system using the three wire lead set or mains plug
the instrument indicates the greatest voltage on the system.
Phase to earth voltage measurement
Note: measured voltage must not exceed 300 V phase to earth.
To measure the voltage of the electrical supply:
1. Set the instrument to the [V] range.
2. Connect the GREEN or (L0) lead to the protective earth (PE) and the
RED or (L1) lead to the phase to be measured.
3. The instrument will display the phase to earth voltage.
Phase to Phase voltage measurement (LT320 and LT330)
NOTE: measured voltage must not exceed 300 V phase to earth.
To measure the voltage of the electrical supply:
1. Set the instrument to the [V] range.
2. Connect the GREEN or (L0/L2) lead to the first phase, and the RED or
(L1) lead to the second phase.
3. The instrument will display the Phase to Phase voltage.
Prior to measuring Zref, all main equipotential bonding must be in place.
Note: Measurements made on live installations by this method may be
lower than the Ze + (R1+R2) from those obtained by continuity testing
methods, due the existence of parallel earth return paths from extraneous
conductive parts.

When connected to all conductors of a three phase system, the instrument
automatically displays the sequence of phase rotation.
To determine phase sequence
1. Connect the Installation Testers as follows:-
Line 1 Red lead to Red phase
Line 2 Green lead to Yellow phase
Line 3 Black lead to Blue phase
2. The symbol is displayed will show the phase sequence:
indicates R – B – Y sequence (or 1:2:3)
indicates R – Y – B sequence (or 1:3:2)
NOTE: If one of the lines is faulty, neither of the symbols is displayed and
just the normal ‘neon’ polarity indication is shown.
16
FREQUENCY HZ (LT320 and LT330) PHASE SEQUENCE (LT320 and LT330)
To measure the frequency of the electrical supply:
1. Set the instrument to the [Hz] range.
2. Connect the GREEN or (L0) lead to the protective Earth (PE) and the
RED or (L1) lead to the phase to be measured.
3. The instrument will display the frequency in Hz.

(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 L-L, L-E, L-N etc 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 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: To change any setting before saving a result, scroll down through
the result using the NEXT/LAST keys. Change the reference number using
the ↑↓ keys and press OK.
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.
To recall the PFC value press LAST or NEXT value if applicable.
17
TEST RESULT STORAGE (LT330 ONLY)
Storing LOOP test results:
Results storage has the following structure:
000, 001…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
000, 001…… job number acts as work folders. Sets of results
can be saved to a particular job number and easily separated when
downloaded.
b01, b02… distribution board number:
c01, c02… circuit reference
Results can be assigned a specific distribution board number and circuit
reference number.
L-E, L-N… - circuit type: allows a test to be defined as the circuit type.
P1,P2,P3 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 logged automatically. This cannot be changed by the user.
To store a result:
1. Make a Z, MaxZ, Zref or R1+R2 loop measurement as descried
earlier and Press STORE.
2. Select Job reference number using ↑↓ keys then press NEXT.

Downloading results to a PC:
1. Run Megger Powersuite Professional or Megger Download Manager on
the PC
2. Select the appropriate downloading instrument from the list
3. Select "Download from Tester"
4. Connect the tester to the PC using the USB test lead.
5. Set the tester range knob to [Snd].
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 will be deleted.
A bar graph shows the progress of the deletion.
WARNING: This operation is not reversible. All data will be deleted.
18
REPLACING BATTERIES
Batteries
Battery type: 8 x LR6 (AA), 1.5 V Alkaline, or 8 x 1.2V NiCAD, or 8 x 1.2V
NiMH
Low battery warning symbol
The battery condition is continuously displayed by the symbol
When the batteries are exhausted, symbol will show and the
isntrument switches off. Batteries should be replaced when 2 bars are
displayed.
If the symbol appears as less than fully charged with new batteries fitted,
check for correct polarity.
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 remove the rear cover release the screw at the bottom of the cover
and lift the cover upwards.
4. Fit new batteries observing the correct polarity as marked on the battery
compartment.
5. Replace the cover.

AUTO POWER DOWN
WARNING: - Incorrect battery cell polarity can cause electrolyte leakage,
resulting in damage to the instrument.
Check that the battery level indicator displays a full charge before using the
instrument. A low battery charge may indicate a reversed cell.
Note: Battery cells should not be left in an instrument which may remain
unused for extended periods of time.
Fuse Blown indication
The fuse blown symbol findicates that an internal fuse has failed. This
instrument is fitted with a factory fitted fuse and should only be replaced by
an authorised Megger repair centre.
To extend battery life the instrument will automatically switch off six
minutes after the last operation. This is extended to 30 minutes when using
the Zref, R1 + R2 or maxZ features.
The instrument can be switched off manually by selecting [OFF] with the
rotary switch, or switched back on again by pressing the [TEST] button.
19

20
PREVENTIVE MAINTENANCE TECHNICAL SPECIFICATION
Clean only with a damp cloth. Do not use any alcohol based cleaning fluids
as they may leave a residue.
General Specification
Only values with tolerances or limits are guaranteed data. Values without
tolerances are for information only.
Voltage measurement
Range: 0 V to 500 V
Accuracy: ±2% ±2 digits
Frequency measurement (LT320 and LT330)
Range: 25Hz to 450Hz
Accuracy: 25.0Hz to 199.9Hz ±0.1Hz
200Hz to 450Hz ±1Hz
Phase rotation indicator (LT320 and LT330)
Three wire identification of phase rotation.
Loop ranges (to EN 61557-3)
3-wire No Trip Loop (Line to Earth)
Supply
(LT310) 100 V - 280 V 45Hz to 65Hz
(LT320 and LT330) 50 V - 280 V 45Hz to 65Hz
Nominal test current: 15mA line to earth
Loop accuracy
0.01 Ω- 9.99 Ω(±5% ±0.03 Ω)
10.0 Ω- 99.9 Ω(±5% ±0.5 Ω)
100 Ω- 999 Ω(±5% ±5 Ω)
1.00 kΩ- 2.00 kΩ(±5% ±30 Ω)