Megger LT310, LT320, LT330 User Manual

LT300 Series
Earth Loop Testers

USER MANUAL

M

G SAFETY 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.

NOTE

THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

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.

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CONTENTS

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

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:

G Caution: refer to accompanying notes
t Equipment protected throughout by Double

Insulation (Class II)

c Equipment complies with current EU directives.

N13117

Equipment complies with ‘C tick’ requirements

3

INTRODUCTION GENERAL DESCRIPTION

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

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 ■■■

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CASE CONTENTS

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 ■

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)

5

LCD DISPLAY FRONT PANEL

6

LT300 Series test lead connections
LT320 and LT320

Mains plug test
lead

Single or 3 phase

Neutral or 2nd
phase connection

USB
connection
(LT330 only)

Memory control keys:
STORE:

LAST/NEXT: Selects the type of location; ie job, distribution

ESC: Aborts a save at any time.
OK: Final operation to save the result.

Store initiates the storing of a test result.

board, circuit, phase etc.

▲ Selects the job, db, circuit number; ie
▼ 01,02,03 etc

Maximum 300 V phase
to earth allowed

LT310

Single phase connection only

LT330 additional controls

Maximum 500 V across
terminals

Maximum 300 V phase
to earth allowed

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).

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PREPARATIONS FOR USE (ALL INSTRUMENTS) GENERAL OPERATING INSTRUCTIONS

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.

Tests lock

The LOCK L indicates when the [Hi] current loop test range is locked
ON.

It is activated by holding down 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

L lock button, and pressing the

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