Megger LTW315, LTW325, LTW335, LTW425 User guide
M
LTW300 Series
Earth Loop testers
User Guide
GSafety warnings:
nSafety Warnings and Precautions must be read and understood before the instrument is used. They must be observed during use.
nThe 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.
nContinuity of protective conductors and earthed equipotential bonding of new or modified installations must be verified before carrying out an earth fault loop impedance test.
nCircuit connections and exposed metalwork of an installation or equipment under test must not be touched.
nDo not leave the instrument connected to the mains supply when not in use.
nDo not leave the instrument connected to the mains supply when performing data download to a PC.
nEnsure that hands remain behind guards of probes/clips when testing.
nThe instrument should not be used if any part of it is damaged.
nThe battery cover must be in place whilst conducting tests.
nTest leads, probes and crocodile clips must be in good order, clean and with no broken or cracked insulation.
nOn 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.
nSome 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 t c
Caution: refer to accompanying notes
Equipment protected throughout by Double Insulation (Class II) Equipment complies with relevant EU Directives
Equipment complies with Australian and New Zealand C Tick requirements
2
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 |
3
4
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.
5
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 |
(LTW335 only) |
1 |
x |
USB cable |
|
1 |
x |
PC software CD |
(LTW335 only) |
1 |
x |
Warning sheet |
(5172-238) |
6
2.2 LCD display
|
Fuse Blown |
Wait |
Refer to |
Temperature |
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User manual |
Test Lead NULLED |
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Indicator |
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RCD Trip |
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Battery status |
|||
Indicator |
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Measured
results
Ranges
Touch voltage
selected Supply noise warning
Zref function selected |
R1+R2 Function |
Loop test |
Loop test extended |
(required before R1+R2 can |
selected |
active |
(Mode 2 operation) |
be measured) |
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|
7
2.3 Top panels
|
Test lead connections |
Loop test function: |
|
|
See section 2.5 |
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(all except LTW315) |
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Z |
LCD Display |
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MaxZ |
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R1+R2 |
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Zref |
|
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|
|
Setup function select
Neck strap slots
Test button
Range selector:
NO-TRIP
High Current
HIGH Res (LTW425)
Volts/Frequency
Setup
PFC display |
Backlight |
Front panel cover |
key |
On/Off |
(folded under instrument) |
8
2.4 Additional controls on the LTW335 (storage and downloading instrument):
2.4.1 Keypad controls
OK |
ESC |
UP/DOWN arrows: |
Aborts a result save |
Scrolls through circuit and |
|
Confirms a test result |
process |
distribution board numbers |
delete request |
|
|
NEXT
Selects test type
Job,
Distribution board,
Circuit,
Phase etc
STORE
Stores last test result
LAST
As next
2.4.2 Range knob controls
Test result delete
Last |
Stored data |
result |
download |
9
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