Megger LTW315 Manuale utente

LTW300 Series

Earth Loop testers

User Guide

GSafety warnings:

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

be observed during use.

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.

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.

Circuit connections and exposed metalwork of an installation or equipment under test must not be touched.

Do not leave the instrument connected to the mains supply when not in use.

Do not leave the instrument connected to the mains supply when performing data download to a PC.

Ensure that hands remain behind guards of probes/clips when testing.

The instrument should not be used if any part of it is damaged.

The battery cover must be in place whilst conducting tests.

Test leads, probes and crocodile clips must be in good order, clean and with no broken or cracked insulation.

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.

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.

Symbols used on the instrument:

G Caution: refer to accompanying notes

tEquipment 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 warning

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)

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

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

Selects test type

Job,

Distribution board,

Circuit,

Phase etc

Last result

recall

Stored data

download

Test result

delete

2.5 Connection panel

2.6 Lid open/closure

1. Open lid by lifting up front panel tab (1).

2. Foldaway underneath instrument (2 & 3) and push into retaining slot (4).

Single or 3 Phase

connection

Earth, Neutral or 2nd phase

connection

Warning

Read user guide

Maximum 300V

Phase to earth

USB connection to

computer port

LTW335 only

3. Preparations for use

The instrument is supplied with batteries already fitted. However when fitting replacement batteries, refer to

section 10.2:

WARNING: -

Never use the instrument with the battery cover removed.

Incorrect battery cell polarity can cause electrolyte leakage, resulting in damage to the instrument.

Always fit a complete new set of batteries, never mix old and new cells.

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 an extended period of

time.

3.1 Preliminary test lead check

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.

3.2 Ingress of moisture

If it is suspected that moisture has entered the instrument, such as extended periods of cold and wet conditions,

the instrument should be dried out prior to use. This can be accelerated by removing the battery cover to assist

drying.

4. General operating instructions

4.1 Backlight operation

Pressing the BACKLIGHT [ ]button will toggle the backlight on and off.

The backlight will automatically switch on at the start and end of a test. It will switch off 5 seconds after the end

of the test.

Backlight brightness can be adjusted whilst in SETUP mode, see SETUP section 8.

4.2 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 should not be altered. However 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

Non-standard test leads

Where fused or longer length leads may be used, the lead resistance will be higher than the value to which the

instrument is calibrated. To add additional offset in the loop measurement, refer to section 8, instrument setup

procedure.

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