Megger LTW315, LTW325, LTW335, LTW425 User guide

LTW300 Series Earth Loop testers

User Guide

G Safety warnings:

n Safety Warnings and Precautions must be read and understood before the instrument is used.

They must be observed during use.

n The earth loop impedance test creates a temporary low resistance path between live and earth for the

duration of the test. This is particularly hazardous with both an instrument fault and an installation fault.

Working practice and hazard avoidance must take care of this risk.

n Continuity of protective conductors and earthed equipotential bonding of new or modified installations

must be verified before carrying out an earth fault loop impedance test.

n Circuit connections and exposed metalwork of an installation or equipment under test must not be

touched.

n Do not leave the instrument connected to the mains supply when not in use. n Do not leave the instrument connected to the mains supply when performing data download to a PC. n Ensure that hands remain behind guards of probes/clips when testing. n The instrument should not be used if any part of it is damaged. n The battery cover must be in place whilst conducting tests. n Test leads, probes and crocodile clips must be in good order, clean and with no broken or cracked

insulation.

n On test leads fitted with a outlet plug and flying leads, never connect test probes, clips, pins or other

objects to the 3 lead plugs because of the danger of electrocution. These leads should only be used by a suitably trained, and competent person.

n Some national safety authorities recommend the use of fused leads for voltage measurement on high

energy systems. If loop tests are made it may cause the fuse to rupture, and so they must be used with caution on voltage testing.

NOTE

THE INSTRUMENTS 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.

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.

Symbols used on the instrument:

G Caution: refer to accompanying notes t Equipment protected throughout by Double Insulation (Class II) c Equipment complies with relevant EU Directives

Equipment complies with Australian and New Zealand C Tick requirements

Contents

Introduction 4 General introduction 5 Unpacking the carton 5 LCD display 6 Top panels 7 Additional controls on the LTW335 8 Keypad controls 8 Range knob controls 8 Connection panel 9 Lid open/closure 9 Preparations for use 10 Preliminary test lead 10 Ingress moisture 10 General operating instructions 10 Backlight operation 10 Test leads 10 Test lead connection 11 Loop testing 12 Description of test methods 12 No-trip test (all instruments) 12 Symbols used during a normal loop test 12 High current test (all instruments) 13 High resolution test (LTW425 only) 13 Performing a loop test 13 Non-tripping loop test (NO TRIP) 13 No-trip testing using the mains socket test lead 13 Phase to Earth loop test 13 Phase to Neutral loop test 13 No-trip loop testing using the RED/GREEN test lead 14 Phase to Earth loop test 14 Phase to Neutral and Phase to Phase loop testing 14 Earth bonded metalwork testing 14 High current loop test 14 High current Phase to Neutral loop test 14 High current Phase to Phase loop test 15 High resolution loop test (LTW425 only) 15 Prospective fault current display (PFC) 15 PFC measurement 15 Possible source of error 15 MaxZ (LTW325, LTW335 and LTW425) 16 Diriving R1 + R2 (LTW325, LTW335 and LTW425) 16 Measuring Zref 16 Voltage and frequency measurement 17 Phase to Earth and Phase to Neutral voltage and frequency measurement 17 Phase to Phase voltage and frequency measurement 17 Saving and downloading test results (LTW335 only) 18 Storing LOOP test results 18 To store a result 18 To store subsequent result 18 To recall test result 18 Downloading results to a PC 19 Deleting test results 19 SETUP menu 20 Setup option selection 20 Fused or long test lead length 20 Backlight brightness adjust 21 Warning and status messages 22 Loop test inhibit or premature termination of a loop test 22 Replacing batteries and fuses 23 Low battery warning symbol 23 Procedure to replace batteries 24 Fuse blown indicator 24 Auto power down 24 Preventative maintenance 24 Technical specification 25 Accessories 26 Repair and Warranty 27

1. Introduction

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 guide describes the operation and functions of the following LTW300 series of loop impedance testers:

LTW315 LTW325 LTW335 LTW425

These instruments are designed and manufactured by:

Megger Limited Archcliffe Road Dover Kent CT17 9EN England

Megger reserves the right to change the specification of these instruments at any time without prior notice.

2. General description

The LTW300 series loop testers are designed for the measurement of loop resistance (Impedance) of fixed electrical installations on single and 3 phase systems.

2.1 Unpacking the carton

Unpack the carton contents carefully. There are important documents that you should keep for future reference.

Please complete the pre-paid 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 for the LTW315, LTW325, LTW335 and LTW425

1 x LTW series loop tester 1 x 2 wire test lead with prods with clips (Red/Green)

1 x Mains lead set (UK, Schuko or Australian, depending on instrument supplied) 8 x AA (LR6) batteries (fitted in instrument) 1 x Warranty card 1 x Certificate of test 1 x Calibration certificate 1 x Owners CD manual 1 x Hard carry case 1 x USB cable (LTW335 only) 1 x PC software CD (LTW335 only) 1 x Warning sheet (5172-238)

RCD Trip

Indicator

2.2 LCD display

Touch

voltage

selected

Measured

results

Fuse Blown

Refer to

User manual

Battery status

Ranges

Supply

noise

warning

R1+R2 Function

selected

Zref function selected (required before R1+R2 can be measured)

Loop test

active

Temperature

Wait

Loop test extended (Mode 2 operation)

Test Lead NULLED Indicator

2.3 Top panels

LCD Display

Setup function

select

Test button

Backlight

On/Off

Test lead connections

See section 2.5

Loop test function: (all except LTW315) Z MaxZ R1+R2 Zref

Neck strap

slots

Range selector:

NO-TRIP High Current HIGH Res (LTW425) Volts/Frequency Setup

Front panel cover

(folded under instrument)

PFC display

key

2.4 Additional controls on the LTW335 (storage and downloading instrument):

2.4.1 Keypad controls

2.4.2 Range knob controls

OK Confirms a test result delete request

ESC Aborts a result save process

UP/DOWN arrows: Scrolls through circuit and distribution board numbers

STORE Stores last test result LAST As next

NEXT Selects test type Job, Distribution board, Circuit, Phase etc

Last result

Stored data download

Test result delete

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