Megger LT300 User manual

M
LT300
High current loop tester
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 and
an installation fault.
■Working practices 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 tests.
■Circuit connections and exposed metalwork of an installation
or equipment under test must not be touched in case of the
presence of hazardous touch voltages
■Do not leave the instrument connected to the mains supply
when not in use.
■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.
■The battery cover must be in place whilst conducting tests.
■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.
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.
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
Symbols used on the instrument:
F Caution: risk of electric shock
GCaution: refer to accompanying notes
tEquipment protected throughout by Double Insulation
(Class II)
c Equipment complies with relevant EU Directives
Equipment complies with ‘C tick’ requirements
Lid open/closure
1. Open lid by lifting up front panel tab (1).
2. Fold-away underneath instrument (2 & 3) and click into
retaining slot (4).

Digital Display Layout
Operation
Important:
Operational voltage range of the LT300 is:
50 V to 550 V.
Operational frequencies of the LT300 are:
16 Hz, 33 Hz, 50 Hz/60 Hz, 125 Hz and 400 Hz (400 V @ 16 Hz).
Auto-Power down:
The instrument will switch off automatically after 4 minutes of no
use. To switch on again press the TEST button or change range.
Test lead check:
Only use the specified test leads. The test leads supplied have an
internal resistance of 0.06 Ω. The LT300 allows for this so accurate
measurements are obtained at the probe tips.
Before each use of the instrument, inspect the test leads, prods
and crocodile clips to confirm that their condition is good, with no
damaged or broken insulation.
On test leads fitted with an 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 competent person.
Supply Category rating:
The LT300 is designed for use on 300 V CAT IV Phase to Earth and
550 V Phase to Phase applications (400 V @ 16 Hz).
Temperature
warning
Fuse
blown
Terminal
voltage
>330 V
Noise
symbol
Low battery
warning
System Frequency

Loop Testing
Select either the 20 Ω or 200 Ω measurement range
depending on:
1. The required measurement resolution 0.01 Ω (20 Ω range) or
0.1 Ω (200 Ω range).
2. The anticipated loop resistance.
3. The required test current taken from the Voltage/Resistance
table below.
Test current varies with supply voltage:
20 Ω range: 200 Ω range:
@ 550 V supply = 27 A @ 550 V supply = 2.7 A
@ 230 V supply = 12 A @ 230 V supply = 1.2 A
@ 115 V supply = 6.0 A @ 115 V supply = 0.6 A
@ 50 V supply = 3 A @ 50 V supply = 0.3 A
Phase-Earth loop measurement
This test is designed for non-RCD protected circuits.
The loop tester will operate over a supply voltage of:
50 V to 550 V (400 V @ 16 Hz).
1. Set the instrument to the 20 Ω range for 0.01 Ω resolution or
the 200 Ω range for 0.1 Ω resolution. Display will show 000 V~
2. Connect the RED (PHASE) lead to the RED socket on the
instrument and the GREEN (EARTH) lead to the GREEN/BLUE
socket (alternatively use the Mains plug test lead Red and Green
connections).
3. Connect the RED lead to Phase and the GREEN lead to Earth (or
connect the mains plug to the wall socket).
4. The supply voltage is displayed and the appropriate system
frequency indicator displayed.
5. Within 5 seconds the loop test starts automatically and the
measured loop value is displayed.
The test can be repeated by pressing the [TEST] button.
Bonded Metalwork Testing
Repeat the above test but with the Green lead connected to the
exposed metalwork.

Phase-Neutral loop measurement
1. Connect the RED (PHASE) lead to the RED socket on the
instrument and the GREEN (EARTH) lead to the GREEN/BLUE
socket (alternatively use the mains plug test lead RED and BLUE
connections).
2. Connect the RED lead to Phase and the GREEN lead to Neutral
(or connect the mains plug to the wall socket).
3. The supply voltage is displayed and the appropriate system
frequency indicator displayed.
4. Within 5 seconds the loop test starts automatically and the
measured loop value is displayed.
The test can be repeated by pressing the [TEST] button.
Phase-Phase loop impedance
1. Connect the RED (PHASE) lead to the RED socket on the
instrument and the GREEN (EARTH) lead to the GREEN/BLUE
socket.
2. Connect the RED lead to Phase1 and the GREEN lead to Phase
2.
3. The supply voltage is displayed and the appropriate system
frequency indicator displayed.
4. The results are displayed as per Phase - Neutral testing above.
Warning indicators
Over range
If the measured loop impedance exceeds the full scale value, the
display will show “>1.” . This is displayed if:
1. Measurement >19.99 Ω on the 20 Ω range or >199.9 Ω on the
200 Ω range. OR
2. A dangerous voltage has been detected on the protective
earthing conductors or bonded metalwork during test. This is
normally due to poor or faulty earthing system.
Over-voltage
The warning triangle will FLASH if the input voltage exceeds
330 V. This is advisory.
If the voltage exceeds 550 V the warning triangle will be
permanently displayed. Remove source of over-voltage
immediately.

Overheating
The thermometer symbol will flash if the instrument is getting hot.
Overheating is shown by a permanently displayed symbol.
Testing is inhibited when the temperature symbol indicator is on.
Voltage Measurement
The voltmeter is designed for AC applications only, up to 550 V
(400 V @ 16 Hz)
Frequency indicators
The frequency indicator shows the system frequency the circuit
is using. It is intended as a guide only. For accurate frequency
measurement a suitable test instrument should be used.
Nominal frequency bands are:
15 Hz to 18 Hz 40 Hz to 70 Hz 260 Hz to 490 Hz
Additional frequency Bands:
33 Hz (29 Hz to 37 Hz) 125 Hz (100 Hz to 142 Hz)
The appropriate indicator is displayed for the supply system
frequency. Testing is only possible when one of the indicators is
displayed.
Battery replacement
Low battery voltage is indicated by the symbol in the
display.
When displayed, loop testing is still possible however the voltmeter
accuracy may be affected.
To replace batteries switch off instrument and disconnect test
leads from the circuit under test.
Remove the battery cover and replace the batteries. Use 8 x 1.5 V
AA (LR6) Alkaline dry cells or NiMH rechargeable cells. Do not mix
old and new batteries.
Warning: OBSERVE CORRECT POLARITY. Incorrect battery
polarity could cause batteries to leak and damage the instrument.
16 Hz 50/60 Hz 400 Hz
16 Hz 50/60 Hz 400 Hz

Fuse replacement
A blown fuse is indicated by the fsymbol in the display.
To replace the fuse remove battery cover and replace fuse with
type:
7 A (F) HBC 50 kA 600 V.
Cleaning: Disconnect the instrument and wipe with a clean cloth
dampened with soapy water or Isopropyl Alcohol (IPA).
SPECIFICATION
Only values with tolerances or limits are guaranteed data. Values
without tolerances are for information only.
Service error is less than ±30% from 0.4 Ω to 200 Ω
Voltage measurement
Range: 0 V to 550 V (400 V @ 16 Hz)
Accuracy: ±2% ±3 V
Range: 16 Hz to 400 Hz
Loop Impedance measurement Phase to Earth
Supply: 50 V to 300 V (400 V @ 16 Hz)
Loop impedance measurement Phase to Phase
Supply: 50 V to 550 V (400 V @ 16 Hz)
When testing close to the source transformer, a system phase
angle of 18° will cause an additional error of -5%. A system phase
angle of 30° will cause an error of -16%.
Nominal test currents :
20 Ω range 200 Ω range
@ 550 V supply = 27 A @ 550 V supply = 2.7 A
@ 230 V supply = 12 A @ 230 V supply = 1.2 A
@ 115 V supply = 6.0 A @ 115 V supply = 0.6 A
@ 50 V supply = 3 A @ 50 V supply = 0.3 A
Loop accuracy 20 Ω range: 0 to 19.99 Ω ±5% ±0.03 Ω
Loop accuracy 200 Ω range: 0 to 199.9 Ω ±5% ±0.5 Ω
Frequency: 16 Hz, 33 Hz, 50/60 Hz,
125 Hz, 400 Hz
Loop ranges: in accordance with EN 61557-3

Environmental
Operating Range: -10°C to +60°C
Operating Humidity: 90% RH at +40°C max.
Storage Range: -25°C to +70°C
Environmental protection: IP54 weatherproof
Battery: 8 x 1,5 V cells IEC AA (LR6)
alkaline or NiMH rechargeable
Battery Life: 60 hours
Fuse: 7A (F) 600 V, 32 x 6 mm HBC
50 kA minimum
Dimensions: 203 mm x 148 mm x 78 mm
Weight: 980 gms
Safety
Meets the requirements of EN61010-1, 300 V Cat IV phase to
earth and 550 V Phase to Phase applications. Refer to safety
warnings supplied.
E.M.C In accordance with IEC61326-1
Operational uncertainties: Refer to www.megger.com
Loop accuracy
Complies with the following parts of EN61557; Electrical safety in
low voltage systems up to 1000 V a.c. and 1500 V d.c.- Equipment
for testing, measuring or monitoring of protective measures:
Part1 - General Requirements
Part3 - Loop resistance
Declaration of Conformity
Hereby, Megger Instruments Limited declares that radio equipment
manufactured by Megger Instruments Limited described in this user
guide is in compliance with Directive 2014/53/EU.
Other equipment manufactured by Megger Instruments Limited
described in this user guide is in compliance with Directives
2014/30/EU and 2014/35/EU where they apply.
The full text of Megger Instruments EU declarations of conformity
are available at the following internet address: megger.com/
eu-dofc.

M
LT300
Hochstrom-Schleifenprüfgerät
Bedienungsanleitung