Megger LTW315 User manual

M
LTW300 Series
Earth Loop testers
User Guide

2
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

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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

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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.

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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)

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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

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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

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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
recall
Stored data
download
Test result
delete

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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

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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.