Megger LT300 Operating Manual

M

LT300 High current loop tester

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 and

an installation fault.

Working practices 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 tests.

n 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

n Do not leave the instrument connected to the mains supply

when not in use.

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 Test leads, probes and crocodile clips must be in good order,

clean and with no broken or cracked insulation.

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

n 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
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 ‘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

Temperature
warning

Fuse
blown

Terminal
voltage
>330 V

Noise
symbol

Low battery
warning

Operation

System Frequency

Important:

Operational voltage range of the LT300 is:

50 V to 550 V.

Operational frequencies of the

N1337

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).