Kewtech KT62 Instruction Manual

KEWTECH

KT62 digital multi function tester

Instruction manual

Contents 1 Safe testing 1

2 Features 3

3 Specification 6

4 Continuity (resistance) tests 9

4.1 Instrument layout 9

4.2 Test procedure 9

5 Insulation tests 11

5.1 The nature of insulation resistance 11

5.1.2 Capacitive current 11

5.1.3 Conduction current 12

5.1.4 Surface leakage current 12

5.1.5 Total leakage current 13

5.2 Damage to voltage sensitive equipment 13

5.3 Preparation for measurement 14

5.4 Insulation resistance measurement 14

6 Loop Impedance tests 17

6.1 Voltage measurement 17

6.2 What is earth fault loop impedance? 17

6.3 Automatic over temperature cut out 17

6.4 The loop impedance test 17

6.5 Loop impedance at 3 phase equipment 19

7 Prospective Short Circuit Current (PSC) tests 21

7.1 What is Prospective Short Circuit? 21

7 2 Testing Prospective Short Circuit Current 21

8 RCD tests 23

8.1 Purpose of RCD Test 23

8.2 What does the RCD test really do 23

8.3 RCD testing 23

8.4 Testing RCD's used to provide supplementary protection 24

8.5 Testing time delayed RCD's 25

8.6 Testing DC sensitive RCD's 25

9 General 26

10 Battery replacement 26

11 Fuse replacement 26

12 Servicing 27

13 Case and strap assembly 27

1 Safe Testing

1

Electricity is dangerous and can cause injury and death. Always
treat it with the greatest of respect and care. If you are not quite
sure how to proceed, stop and take advice from a qualified person.

1 This instrument must only be used by a competent and trained person

and operated in strict accordance with the instructions. Kewtech will
not accept liability for any damage or injury caused by misuse or non­compliance with the instructions or with the safety procedures.

2 It is essential to read and to understand the safety rules contained in

the instructions. They must always be observed when using the
instrument.

3 This instrument is intended only for single phase operation at 230V AC

+10%-15% phase to earth or phase to neutral operation, and then
only for loop, prospective short circuit current (PSC) and RCD testing.
For use in the continuity testing and insulation testing modes this
instrument must be used ONLY on circuits which are de-

energised.

4 When conducting tests do not touch any exposed metalwork

associated with the installation. Such metalwork may become live for
the duration of the test.

5 Never open the instrument case (except for fuse and battery

replacement and in this case disconnect all leads first) because
dangerous voltages are present. Only fully trained and competent
electrical engineers should open the case. If a fault develops, return the
instrument to Kewtech for inspection and repair.

6 If the overheat symbol appears in the display disconnect the

instrument from the mains supply and allow to cool down.

7 For loop impedance tests to prevent unwanted tripping during loop

testing all residual current devices (RCDs) must be taken out of the
circuit and temporarily replaced with a suitably rated MCB unit. The
RCD must be replaced after the loop test is completed.

8 If abnormal conditions of any sort are noted (such as a faulty display,

unexpected readings, broken case, cracked test leads, etc) do not use
the tester and return it to Kewtech for repair.

9 For safety reasons only use accessories (test leads, probes, fuses,

cases, etc) designed to be used with this instrument and
recommended by Kewtech. The use of other accessories is prohibited
as they are unlikely to have the correct safety features.

10 When testing, always be sure to keep your fingers behind the safety

barriers on the test leads.

Safe testing211 During testing it is possible that there may be a momentary

degradation of the reading due to the presence of excessive transients
or discharges on the electrical system under test. Should this be
observed, the test must be repeated to obtain a correct reading. If in
doubt, contact Kewtech.

12 The sliding shutter on the back of the instrument is a safety device. The

instrument should not be used if it is damaged or impaired in any way,
but returned to Kewtech for attention.

13 Kewtech recommends the use of fused test leads particularly when

measuring voltages in high energy circuits. Where assessments show
that the risk is significant, then the use of fuse test leads constructed in
accordance with the HSE Guidance Note GS38 should be used. The
test accessories used with this instrument for loop impedance and
RCD tests are all fused.

14 Do not operate the function selector whilst the instrument is

connected to a circuit. If, for example, the instrument has just
completed a continuity test and an insulation test is to follow,
disconnect the test leads from the circuit before moving the selector
switch.

15 Do not rotate function dial when test button is depressed. If the

function switch is inadvertently moved to a new function when the test
button is depressed or in lock-down position the test in progress will
be halted.

16 Always check the test lead resistance before carrying out tests. This

ensures the leads are ok before taking measurements. The resistance
of leads and/or crocodile clips may be significant when measuring low
resistances. If crocodile clips can be avoided for low resistance
measurements , this will reduce the error due to lead accessories

17 When carrying out Insulation Resistance tests, always release the test

button and wait for charged capacitances to totally discharge before
removing the test leads from the test circuit.

BATTERY LIFE

Always switch the selector dial to the OFF position after each testing
period. This will conserve battery power.

INSULATION/CONTINUITY TESTS

Only use the test leads supplied with this tester and always ensure that
they are plugged fully into the unit’s 4mm terminals to guarantee a
sound and proper connection.

2 Features

3

Connector

Live circuit LED

Phase switch
Polarity switch
Continuity null switch

RCD rated tripping
current switch

Function switch

Wiring check LED

LCD display

Test button

LCD display

Test Lead with IEC Connector

Test Lead for Continuity

and Insulation Testing

Fig. 1

Features4The KT62 Multi-Function tester performs six functions in one instrument.

1 Continuity tester

2 Insulation resistance tester

3 Loop impedance tester

4 Prospective short circuit current tester

5 RCD tester

6 Mains voltage warning when operating the loop impedance and

RCD mode.

The tester is designed to Safety Standard IEC 1010-1/BS EN 61010-1
CAT III(300V).

The instrument is supplied with:

1A distribution board or lighting circuit test lead for

LOOP/PSC/RCD testing.

2 A lead for LOOP/RCD testing at socket outlets.

3 A lead for insulation and continuity testing.

4 External Earth Probe for loop testing.

In the insulation resistance testing mode the instrument provides a rated
current of1mA as required in BS 7671 (IEE Wiring Regulations) and BS EN
61557-2 1997.

In the continuity testing mode the instrument provides a short circuit
current of 200mA as required in BS 7671 (IEE Wiring Regulations) and BS
EN 61557-4 1997.

Continuity and insulation resistance functions have the following features:

Live circuit warning A colour coded LED warns if the circuit

under test is live.

Continuity Null Allows automatic subtraction of test

lead resistance from continuity
measurements.

Polarity switch Allows switching of polarity during

continuity tests.

Auto discharge Electric charges stored in capacitive circuits

are discharged automatically after testing
by releasing the test button.

Features

5

Loop impedance, PSC and RCD testing functions have the following
features:

Voltage level In the LOOP/PSC/RCD modes, supply

voltage is displayed when the instrument is
connected to the supply until the test button
is pressed.

Wiring check Three LEDs indicate if the wiring of the

circuit under test is correct.

Over temperature Detects overheating of the internal
protection resistor (used for LOOP and PSC tests) and of

the current control MOS FET (used for RCD
tests) displaying a warning symbol and
automatically halting further measurements.

Phase angle selector The test can be selected from either the

positive (0˚) or from the negative (180˚) half­cycle of voltage. This selector is used in the
RCD mode to obtain the maximum trip time
of an RCD for the test selected.

DC Test Allows testing of RCDs which are sensitive to

DC fault currents.

Auto data hold Holds the displayed reading for a time after

the test is complete.

Auto power off Automatically switches the instrument off

after a period of approximately 10 minutes.
The Auto power off made can only be
cancelled when the Function switch is
switched to the OFF position and then back
on.

V-NE Monitoring Automatically aborts measurement when the
Circuit N-E voltage rises to 50V or greater on RCD

ranges.

Specification

6

Measurement Specification

Function

Open Circuit
Voltage (DC)

Short Circuit

Current

Range Accuracy

Function

Open Circuit
Voltage (DC)

Rated

Current

Range Accuracy

Function

Rated

Voltage (AC)

Nominal Test

Current at 0Ω

External Loop

Range

Accuracy

Continuity

Greater than

6V

Greater than

200mA as per

BS7671

20/200/2000Ω

Auto-Ranging

±(1.5%rdg

+3dgt)

250V+40%

-0%

1mA or greater

@ 250kΩ as per

BS7671

20/200MΩ

Auto-Ranging

±(1.5%rdg

+3dgt)

500V+30%

-0%

1mA or greater

@ 500kΩ as per

BS7671

20/200MΩ

Auto-Ranging

±(1.5%rdg

+3dgt)

1000V+20%

-0%

1mA or greater

@ 1MΩ as per

BS7671

20/200MΩ

Auto-Ranging

±(1.5%rdg

+3dgt)

Insulation

Resistance

230V+10% -15% 50Hz

230V+10% -15% 50Hz

230V+10% -15% 50Hz

Loop

Impedance

25A

15mA

15mA

±(3%rdg+4dgt)

±(3%rdg+8dgt)

±(3%rdg+4dgt)

20Ω

200Ω

2000Ω

230V+10%

-15% 50Hz

Prospective

Short Circuit

Current

(PSC)

15mA

25A

25A

PSC accuracy is

derived from

measured loop

impedance

specification

and measured

voltage

specification

200A

2000A

20kA

Specification

7

Function

Rated

Voltage (AC)

Trip Current

Trip Current

Duration

Accuracy

Function

Rated voltage

Measuring

Range

Accuracy

Voltage measurement-

100-250V 100-250V 3% rdg

RCD
x 1/2

230V+10%

-15% 50Hz

230V+10%

-15% 50Hz

Trip Current:

-10% +0% of
range at 230V

Trip Current:

+10% -0% of

range at 230V

Trip Current:

+10% -0% of

range at 230V

RCD

x 1

10/30/100/300/

500/1000 mA

10/30/100/300/

500/1000 mA

2000ms

2000ms

1000mA

@200ms

Trip Current:

±10% of

range at 230V

RCD

x 5

230V+10%

- 15% 50Hz

10 mA

30/100/300mA

(Note: on x5 range

max. current that can

be generated is 1A)

50ms

Trip

Time±

(1% rdg

+3dgt)

To prevent wrong connection of test leads and to maintain safety, the
dedicated terminals used for continuity and insulation tests are
automatically covered when using the terminals for loop impedance, PSC
and RCD tests.

Instrument dimensions130 X 183 X 100mm

Instrument weight 1130g including batteries.

Reference conditions Specifications are based on the following

conditions except where otherwise stated:-

1 Ambient temperature: 23±2˚C

2Relative humidity 45% to 75%

3Position: horizontal

4AC power source 230V, 50Hz

5 DC power source: 12.0 V, ripple content

1% or less

6Altitude up to 2000m

Specification8Battery type Eight AA ALKALINE batteries.

Low battery warning symbol appears in the display and the

buzzer beeps if the battery voltage drops
below 7.8V.

Operating temperature 0 to +40˚C, relative humidity 80% or less, no
and humidity. condensation.

Storage temperature -10 to +50˚C, relative humidity 75% or less,
and humidity no condensation.

LED indication of live Illuminates if there is an alternating voltage of
circuit warning 50V AC or more in the circuit under test

before continuity or insulation resistance tests.
When DC voltage is detected across the
measuring terminal the LED lights up.

LED indication of The P-E and P-N LEDs illuminate when the
correct polarity wiring of the circuit under test is correct.

The reverse lamp is lit when P and N are
reversed.

Auto data hold In the loop impedance, PSC and RCD test

functions, the LCD reading is automatically
frozen for 3 seconds after measurement.

Display The liquid crystal display has 3 1/2 digits with a

decimal point and units of measurement (Ω,
MΩ, A, kA,V and ms) relative to selected
function. The display is updated approximately
five times per second.

Overload protection The continuity test circuit is protected by a

0.5A 600V fast acting (HRC) ceramic fuse
mounted in the battery compartment, where a
spare fuse is also stored.

The insulation resistance test circuit is
protected by a resistor against 1000 V AC for
10 seconds.

Mains Voltage On connecting test leads to the circuit under
Indication test on LOOP, PSC and RCD ranges, the LCD

reads V-PE. Sign ‘V-PE Lo’ or ‘V-PE Hi’ is also
shown when the voltage is 100V or less, or
260V or greater respectively.

+

_

LO

4 Continuity
(resistance) tests

9

Warning: Ensure that circuits to be tested are not live.

Disconnect the instrument from the circuit under test before
operating the function switch.

To select the low resistance range select ‘CONTINUITY’.

4.1 Instrument layout - see Fig 1 on page 3.

4.2 Test Procedure

The object of continuity testing is to measure only the resistance of the
parts of the wiring system under test. This measurement should not
include the resistance of any test leads used. The resistance of the test
leads needs to be subtracted from any continuity measurement. The KT62
is provided with a continuity null feature which allows automatic
compensation for any test lead resistance.

You should only use the test leads supplied with the instrument.

Proceed as follows:-

1 Select the continuity test by rotating the function dial.

2 Connect the ends of the test leads firmly together (see Fig 2) and press

and lock down the test button. The value of the lead resistance will be
displayed.

3 Operate the Continuity Null button, this will null out the lead

resistance and the indicated reading should go to zero.

4Release the test button. Press the test button and ensure the display

reads zero before proceeding. While using the Continuity null function,
the Ω symbol will flash. The null value will be stored even if the
function switch is turned to the OFF position. This memorized null
value can be cancelled by disconnecting the test leads and pushing the
Continuity Null button with the test button pressed or locked. When

Fig. 2

Continuity

(resistance) tests

10

this is cancelled you will know because the Ω symbol will not flash.

CAUTION - before taking any measurements always check the leads
have been zeroed.

5 Connect the test leads to the circuit whose resistance is required (see

Fig 3 for a typical connection arrangement), having first made sure
that the circuit is not live. Note that the live circuit warning lamp
will illuminate if the circuit is live - but check first anyway!

6Press the test button and read the circuit resistance from the display.

The reading will have the test lead resistance already subtracted if the
Continuity null function has been used.

7 Note that if the circuit resistance is greater than 20Ω the instrument

will autorange to the 200Ω, if it is greater than 200Ω it will autorange
to the 2000Ω range.

Note: If the reading is greater than 2000Ω the overange symbol
‘OL’ will remain displayed.

The KT62 is provided with a facility to change the polarity of the test
current used by the instrument during continuity tests. To use this function
proceed as follows:-

1Perform a continuity test as outlined in the procedures above.

2Operate the polarity switch if required.

3Repeat the continuity tests and the polarity of the test current will be

reversed.

Temporary link

Test at socket

between L and E

Fig 3

5 Insulation tests

11

Warning: Ensure that circuits to be tested are not live.

Disconnect the instrument from the circuit under test before
operating the function switch.

To select the insulation resistance range select ‘INSULATION’.

5.1 The nature of insulation resistance

Live conductors are separated from each other and from earth metal by
insulation, which has a resistance which is high enough to ensure that the
current between conductors and to earth is kept at an acceptably low
level. Ideally insulation resistance is infinite and no current should be able
to flow through it. In practice, there will normally be a current between
live conductors and to earth, and this is known as leakage current. This
current is made up of three components, which are:-

1. capacitive current

2. conduction current, and

3. surface leakage current.

5.1.2 Capacitive Current

The insulation between conductors which have a potential difference
between them behaves as the dielectric of a capacitor, the conductors
acting as the capacitor plates. When a direct voltage is applied to the
conductors, a charging current will flow to the system which will die away
to zero (usually in less than a second) when the effective capacitor
becomes charged. This charge must be removed from the system at the
end of the test, a function which is automatically performed by the KT62.
If an alternating voltage is applied between the conductors, the system
continuously charges and discharges as the applied voltage alternates, so
that there is a continuous alternating leakage current flowing to the
system.

Insulation tests

12

Insulation (acting as dielectric)

Insulation (acting as resistance)

Conductor (acting

as capacitor plates)

Conductors

Capacitive effect

Insulation

Conductors

Surface leakage current

Fig 4

5.1.3 Conduction Current

Since the insulation resistance is not infinite, a small leakage current flows
through the insulation between conductors. Since Ohm's Law applies, the
leakage current can be calculated from

Leakage current (µA) =

applied voltage (V)

insulation resistance (MΩ)

Fig 5

5.1.4 Surface Leakage Current

Where insulation is removed, for the connection of conductors and so on,
current will flow across the surfaces of the insulation between the bare
conductors. The amount of leakage current depends on the condition of
the surfaces of the insulation between the conductors. If the surfaces are
clean and dry, the value of the leakage current will be very small. Where
the surfaces are wet and/or dirty, the surface leakage current may be
significant. If it becomes large enough, it may constitute a flashover
between the conductors.

Whether this happens depends on the condition of the insulation surfaces
and on the applied voltage; this is why insulation tests are carried out at
higher voltages than those normally applying to the circuit concerned.

Fig 6

Resistance effect

Insulation tests

13

5.1.5 Total Leakage Current

The total leakage current is the sum of the capacitive, conduction and
surface leakage current described above. Each of the currents, and hence
the total leakage current, is affected by factors such as ambient
temperature, conductor temperature, humidity and the applied voltage.

If the circuit has alternating voltage applied, the capacitive current (5.1.2)
will always be present and can never be eliminated. This is why a direct
voltage is used for insulation resistance measurement, the leakage current
in this case quickly falling to zero so that it has no effect on the
measurement. A high voltage is used because this will often break down
poor insulation and cause flashover due to surface leakage (see 5.1.4), thus
showing up potential faults which would not be present at lower levels.
The insulation tester measures the applied voltage level and the leakage
current through the insulation. These values are internally calculated to
give the insulation resistance using the expression:-

Insulation resistance (MΩ) =

Test voltage (V)

Leakage current (µA

As the capacitance of the system charges up, so the charging current falls
to zero and a steady insulation resistance reading indicates that the
capacitance of the system is fully charged. The system is charged to the full
test voltage, and will be dangerous if left with this charge. The KT62
provides an automatic path for discharging current as soon as the test
button is released to ensure that the circuit under test is safely discharged.

If the wiring system is wet and/or dirty, the surface leakage component of
the leakage current will be high, resulting in low insulation resistance
reading. In the case of a very large electrical installation, all the individual
circuit insulation resistances are effectively in parallel and the overall
resistance reading will be low. The greater the number of circuits
connected in parallel the lower will be the overall insulation resistance.

5.2 Damage to Voltage-Sensitive Equipment

An increasing number of electronic-based items of equipment are being
connected to electrical installations. The solid state circuits in such
equipment are likely to be damaged by the application of the levels of
voltage used to test insulation resistance. To prevent such damage, it is
important that voltage-sensitive equipment is disconnected from the
installation before the test is carried out and reconnected again
immediately afterwards. The devices which may need to be disconnected

Insulation tests14before the test include:-

▲ Electronic fluorescent starter switches
▲ Passive infra-red detectors (PIRs)
▲ Dimmer switches
▲ Touch switches
▲ Delay timers
▲ Power controllers
▲ Emergency lighting units
▲ Electronic RCDs
▲ Computers and printers
▲ Electronic point-of-sale terminals (cash registers)
▲ Any other device which includes electronic components.

5.3 Preparation for measurement

Before testing, always check the following:-

1 The ‘low battery’ Indication is not displayed

2 There is no visually obvious damage to the tester or to the test

leads

3 Test the continuity of the test leads by switching to continuity test

and shorting out the lead ends. A high reading will indicate that
there is a faulty lead or that the fuse is blown.

4 Make sure the circuit to be tested is not live. A warning

lamp is lit if the instrument is connected to a live circuit but test
the circuit as well!

5.4 Insulation resistance measurement

The KT62 has a selectable, triple test voltage of 250V, 500V and 1000V
DC.

1 Select the insulation resistance setting by rotating the function

dial to the required test voltage - 250V, 500V or 1000V as
indicated under the ‘insulation’ test section of the functional
switch, after making sure that the instrument is not connected to
a live circuit.

2 Attach the test leads to the instrument and to the circuit or the

appliance under test (see Figs 7 & 8)

+

_

LO

Insulation tests

15

All fuses in or circuit

breakers closed

Mains switch open

Equipment disconnected

Switches closed

Lamps out

Reading not less

than 0.5 MΩ

Main

switch

open

Note: insulation testing must only be undertaken on

de-energised circuits

Fig 7

3 If the mains warning lamp lights and/or the buzzer sounds do not

press the test button but disconnect the instrument from the circuit.
Make the circuit dead before proceeding.

Fig 8

4Press the test button when the display will show the insulation

resistance of the circuit or the appliance to which the instrument is
connected.

5 Note that if the circuit resistance is greater than 20MΩ the instrument

will automatically range to the 200MΩ reading.

Insulation tests166When testing is complete release the test button before disconnecting

the test leads from the circuit or from the appliance. This will ensure
that the charge built up by the circuit or the appliance during insulation
test is dissipated in the discharge circuit. In the discharging process, an
LED illuminates and the live circuit warning buzzer will sound.

CAUTION

Never turn the function dial whilst the test button is depressed as
this may damage the instrument. Never touch the circuit, test lead
tips or the appliance under test during insulation testing.

Always release the test button first after testing before removing
the test leads from the circuit. This is to ensure that charges
stored in the circuit capacitance have been totally discharged.

Note: If the reading measured greater than 200MΩ the over range

reading ‘OL’ will be displayed.

6 Loop impedance
tests

17

Disconnect the instrument from the circuit under test before
operating the function switch.

To select the loop testing range select ‘LOOP’.

6.1 Voltage Measurement

When the tester is set to the loop test function, mains voltage is displayed
as soon as the instrument is connected for test. This voltage display is
automatically updated five times every seconds. The voltage function
operates whenever the test button is in the up position.

6.2 What is earth fault loop impedance?

The path followed by fault current as a result of a low impedance fault
occurring between the phase conductor and earth is called earth fault
loop. Fault current is driven round the loop by the supply voltage, the
amount of current depending on the voltage of the supply and on the
impedance of the loop. The higher the impedance, the lower will be the
fault current and the longer it will take for the circuit protection (fuse or
circuit breaker) to operate and interrupt the fault.

To make sure that fuses will blow or that circuit breakers will operate
quickly enough in the event of a fault, the loop impedance must be low, the
actual maximum value depending on the characteristics of the fuse or the
circuit breaker concerned. The IEE Regulations (BS 7671) provides tables
showing the maximum permissible values of loop impedance in circuits
protected by various fuses and circuit breakers. Every circuit must be
tested to make sure that the actual loop impedance does not exceed that
specified for the protective device concerned.

6.3 Automatic over-temperature cut-out

During the short test period the instrument operates at high power. If
frequent tests are conducted over a prolonged period of time, the internal
test resistor will overheat. When this happens, further tests are
automatically inhibited and the over-temperature symbol appears in the
display. The instrument must then be left to cool down, after which testing
may be resumed.

6.4 The loop impedance test

Since the earth fault loop is made up of conducting path which includes the
supply system back to the supply transformer, it follows that loop testing
can only be carried out after the mains supply has been connected. In
many cases, any RCD in the circuit will be tripped by this test, which draws
current from the phase and returns it through the earth system. The RCD

Loop impedance

tests

18

will see this as the type of fault it is designed to protect against, and will
trip. To prevent this unwanted RCD tripping during loop testing, any RCD
must be taken out of circuit and temporarily replaced with a suitably rated
MCB unit. The RCD will need to be replaced after the loop test is
completed.

WARNING

Do not proceed with testing unless the P-E and P-N lamps are lit
to confirm that the wiring is correctly connected. Should these two
lamps not be lit, investigate the wiring connections of the
installation and rectify any faults before proceeding with the test.
If the red LED is lit do not proceed.

1 Set the instrument to loop test 20Ω range.

2 If testing sockets, connect the plug lead to the KT62 and push the

moulded plug into the socket to be tested (see Fig 9).

3 Check that the wiring lamps are lit Green (PE), Green (PN) and the

third red LED is OFF

4Note the mains voltage displayed by the instrument.

5Press the ‘Press to test’ button. The value of the measured loop

impedance will be displayed with the appropriate units. The test will
start at the sound of a bleep. Whilst the test is being conducted the
display will show a series of moving square symbols (see below). When
these stop the measurement value will be displayed.

6 If testing lighting or other circuits, connect the three-wire lead to the

KT62, connect the red (phase) lead to the phase connection of the
circuit under test, connect the black (neutral) lead to the neutral
connection of the circuit under test, and connect the earth lead to the
earth associated with the circuit. (see Fig 10).

7 The measuring ranges 200Ω and 2000Ω use a low test current.

Therefore it will be possible to carry out a loop impedance test in the
presence of RCD's rated at 30mA or above (assuming that there is no
other earth leakage on the circuit being tested). Note that readings
below 15Ω will be subject to significant variances due to the fact that

Loop impedance
tests

19

a low test current is more susceptible to interference. This current
carries the advantage of reducing the risk of the RCD tripping but
carries the disadvantage that it produces weaker signals for the
measurement circuits to process.

8 If the instrument measures greater than 20Ω the over-range symbol

‘OL’ will be displayed. If this is the case, switch the instrument up a
range to the 200Ω range and repeat the test to obtain a satisfactory
reading. If on the 200Ω range the over-range symbol is again displayed,
switch the instrument up a range to the 2000Ω range and repeat the
test.

Note: Do not connect phase to phase as this instrument is rated at 230V.

9 External Earth Probe: the phase-earth loop impedance of exposed

metalwork (e.g. pipes/conduit ) can be tested using the external earth
probe supplied with the instrument. Connect the unit to the socket as
normal ensuring that the test button is not pressed or locked down.
Plug the external earth probe into the external earth probe socket,
ensuring the probe is held with fingers behind the finger guard. The red
LED will switch on as well as the two green LEDs remaining on. The
digital display will change to ‘LO’. Initially the buzzer will sound
indicating that the probe is plugged in. When this probe is connected
to an earth point, the red LED will switch off and the display will revert
to voltage mode. If the wiring status LEDs (two green LEDs) indicate
correct wiring, press the test button. A test will be initiated using the
external earth probe as the earth return path (the earth of the mains
lead will not be part of the circuit). During the test the symbols below
will be displayed indicating that a test is in progress. They are different
to the previous symbols for a normal earth test to indicate the probe
is being used. When the symbols stop, the measurement value will be
displayed.

6.5 Loop impedance at 3 phase equipment

Use the same procedure as in 6.4 above ensuring that only one phase is
connected at a time i.e.:

First Test: red prod to phase 1, black prod to neutral,
green crocodile clip to earth.
Second Test: red prod to phase 2, black prod to
neutral, green crocodile clip to earth etc.

Loop impedance

tests

20

WARNING

Never connect the instrument to two phases at the same time.

Testing as described in 6.4 and 6.5 above will measure the Phase-Earth
loop impedance. If you wish to measure the Phase-Neutral loop
impedance then the same procedure should be followed except the earth
clip should be connected to the neutral of the system i.e.: the same point
as the black neutral probe.

If the system has no neutral then you must connect the black neutral probe
to the earth i.e.: the same point as the green earth clip. This will only work
if there is no RCD in this type of system.

Note : 200Ω Loop range
This range uses complex sampling and averaging routines. Therefore if the
circuit under test changes in value during the period when the unit is
plugged in for test, the resulting measurement displayed will be the
average of all values. If the reading between successive test button presses
changes significantly the resulting displayed value may be inaccurate.

Fig 9

Fig 10

Black

neutral

Red phase

Green

earth

7 Prospective
short circuit
current (PSC)
tests

21

WARNING

Never connect this instrument across two phases. Never attempt
to measure the phase to phase prospective short circuit current.

7.1 What is Prospective Short Circuit Current?

The Prospective Short Circuit or Fault Current at any point within an
electrical installation is the current that would flow in the circuit if no
circuit protection operated and a complete (very low impedance) short
circuit occurred. The value of this fault current is determined by the supply
voltage and the impedance of the path taken by the fault current.
Measurement of Prospective Short Circuit Current (PSC) can be used to
check that protective devices within the system will operate within safety
limits and in accordance with the safe design of the installation.

7.2 Testing Prospective Short Circuit Current

PSC is normally measured at the distribution board between the phase and
neutral, or at a socket outlet between phase and earth.

If testing at a distribution board proceed as follows:-

1 Select the 200A, 2000A or 20kA range.

2 Connect the distribution board lead to the IEC socket on

the instrument.

3 Connect the red phase probe of the lead to the phase of the

system, the black probe to the neutral of the system and the
green crocodile clip to the neutral of the system.

4 Ensure that the two green P-E and P-N LEDs are on and the third

red LED is OFF.

5Press the test button. A test will start at the sound of a bleep.

6Wait for the display to clear to zero before conducting another

test or disconnecting the instrument. It is good practice to
disconnect the phase lead first.

Note: For loop impedances greater than 50Ω (PSC less than 5A

approx) it is not possible to obtain an accurate PSC reading and
the unit will lock out the PSC range by displaying the ‘OL’ over­range symbol.
If the PSC ranges are selected whilst connected to a socket
outlet via the mains lead, a test will take place between Phase
and Earth due to fixed wiring of the moulded mains plug i.e. a
Phase-Earth fault current test.

Prospective

short circuit

current (PSC)

tests

22

Note: 200A PSC range

This range uses complex sampling and averaging routines. Therefore if the
circuit under test changes in value during the period when the unit is
plugged in for test, the resulting measurement displayed will be the
average of all values. If the reading between successive test button presses
changes significantly the resulting displayed value may be inaccurate.

Note: PSC function has a power factor correction of 0.84.

PSC =

V

x 0.84

A

8 RCD tests

23

Disconnect the instrument from the circuit under test before
operating the function switch.

To select the RCD test range select ‘RCD’.

8.1 Purpose of the RCD test

The RCD must be tested to ensure that operation takes place quickly
enough to ensure that there is unlikely to be serious danger to a person
experiencing an electric shock from the system. This test must NOT be
confused with that taking place when the ‘test’ button on the RCD is
pressed; operation of the test button simply trips the breaker to ensure
that it is working, but does not measure the time taken to break the
circuit.

CAUTION

The x5 setting on the 300mA will output 5x300mA. However the
x5 current for 500mA and for 1000mA is limited to a maximum of
1000mA. In DC mode the 1000mA range is limited to 500mA
maximum.

8.2 What does the RCD test really do?

The RCD is designed to trip out when the difference between the phase
current and the neutral current (this is called the residual current) reaches
the tripping value (or rating) of the device. The tester provides a carefully
preset value of residual current depending on its setting and then
measures the time lapse between the application of the current and the
operation of the RCD.

8.3 RCD testing

1 Set the RCD rated tripping switch to the trip rating of the RCD

under test.

2 Set the function switch to x1/2 for the ‘no trip’ test, which

ensures that the RCD is operating within its specification and is
not too sensitive.

3Press the phase selector switch to indicate O˚ in the display.

4 Connect the instrument to the RCD to be tested either via a

suitable socket outlet (see fig 9) or using the test lead set
(see fig 10).

5 Make sure that the P-E and P-N wiring check lamps are lit and the

wiring incorrect LED is not lit. If they are not, disconnect the

RCD tests

24

tester and check the wiring for a possible fault.

6 If the lamps are correctly lit, press the test button to apply half

the rated tripping current for 2000 ms, when the RCD should
not trip. The PN and PE LEDs should remain on indicating the
RCD has not tripped.

7 Press the phase selector switch to indicate 180˚ in the display

and repeat the test.

8 In the event of the RCD tripping, the trip time will be displayed,

but the RCD maybe faulty.

9 Set the function switch to x1 for the ‘trip’ test, which measures

the time taken for the RCD to trip with the set residual current.

10 Press the phase selector switch to indicate 0˚ on the display.

11 Make sure that the P-E and P-N wiring check lamps are lit. If they

are not, disconnect the tester and check the wiring for a possible
fault.

12 If the lamps are lit, press the test button to apply full rated

tripping current and the RCD should trip, the tripping time being
shown on the display. If the RCD has tripped the PN and PE
LEDs should be off. Check this is so.

13 Press the phase selector switch to indicate 180˚ in the display

and repeat the test.

14 Make sure to keep clear of earthed metal during the

operation of these tests.

8.4 Testing RCDs used to provide supplementary protection. (x5 trip test)

RCDs rated at 30mA or less are sometimes used to provide extra
protection against electric shock. Such RCDs require a special test
procedure as follows:-

1 Set the function switch to x5 for the ‘fast’ trip test.

2Press the phase selector switch to indicate 0˚ in the display.

3 Connect the test instrument to the RCD to be tested.

4 Make sure that the P-E and P-N wiring check lamps are lit. If they

are not, disconnect the tester and check the wiring for a possible
fault.

5 If the lamps are lit, press the test button to apply a test current

25

of 150mA where the RCD should trip within 40ms, the tripping
time being shown on the display.

6Press the phase selector switch to indicate 180˚in the display and

repeat the test.

7 Make sure to keep clear of earthed metal during the

operation of this tests.

8.5 Testing time delayed RCDs

RCDs with a built-in time delay are used to ensure discrimination, that is,
that the correct RCD operates first. Testing is carried out in accordance
with item 8.3 above, except that the displayed tripping times are likely to
be longer than those for a normal RCD. Since the maximum test time is
longer, there may be danger if earthed metal is touched during the test.

Make sure to keep clear of earthed metal during the operation of
this test.

Note: If the RCD does not trip the tester will supply the test current for

a maximum of 2000ms on the x1/2 and x1 ranges. The fact that
the RCD has not tripped will be evident because the PN and PE
LEDs will still be on. The test current will flow for nominally
50mS on the x5 range.

8.6 Testing DC sensitive RCDs

The KT62 has a facility to test RCDs that are sensitive to DC fault currents.
Proceed as follows:

1 Set the RCD rated tripping current.

2 Set the function switch to DC test position.

3 The phase is fixed at 0˚.

4 Make sure that the P-E and P-N wiring check lamps are lit. If they

are not, disconnect the tester and check the wiring for a possible
fault.

5 If the lamps are lit, press the test button to apply rated tripping

current and the RCD should trip, the tripping time being shown
on the display.

Make sure to keep clear of earthed metal during the operation of
this test.

RCD tests

26

The test button can be locked down for ease of use by pressing it and
turning clockwise. Do not forget to release test button by turning it anti­clockwise before disconnecting the instrument from the test points.
Failure to do so may leave the tested circuit in a charged condition when
carrying out insulation tests.

The instrument is provided with a sliding cover to ensure that leads for
testing continuity and insulation resistance cannot be connected at the
same time as test leads for loop testing and RCD testing. If this sliding
cover is damaged so that it fails to perform its function, do not use the
instrument and return it to Kewtech for attention.

When the display shows the low battery indication, , disconnect the
test leads from the instrument. Remove the battery cover and the
batteries. Replace with eight (8) new 1.5V AA batteries, taking care to
observe correct polarity. Replace the battery cover.

The continuity test circuit is protected by a 600V 0.5A HRC ceramic type
fuse situated in the battery compartment, together with a spare. If the
instrument fails to operate in the continuity test mode, first disconnect the
test leads from the instrument. Next remove the battery cover, take out
the fuse and test its continuity with another continuity tester. If it has failed,
replace it with a spare, before refitting the battery cover. Do not forget to
obtain a new fuse and place it in the spare position.

If the instrument will not operate in the loop impedance, PSC and RCD
modes, it may be that the
protective fuses fitted on the
printed circuit board have
blown. If you suspect that
the fuses have failed, return
the instrument to Kewtech
for service - do not attempt
to replace the fuses yourself.

9 General

10 Battery

replacement

11 Fuse

replacement

+

_

LO

Fig 11

Spare fuse

Screw

Fuse

Battery

12 Servicing

27

13 Case and
strap assembly

If this tester should fail to operate correctly, return it to Kewtech stating
the exact nature of the fault. Before returning the instrument ensure that:

1 The leads have been checked for continuity and signs of damage.

2 The continuity mode fuse (situated in the battery compartment)

has been checked.

3 The batteries are in good condition.

Please remember to give all the information possible concerning
the nature of the fault, as this will mean that the instrument will
be serviced and returned to you more quickly.

Return the instrument to:

Service Department
Kewtech Corporation Limited
76 St. Catherine’s Grove
Lincoln LN5 8NA

Regular re-calibration is recommended for this instrument. Kewtech
recommends that with normal use, the instrument be calibrated at least
once in every 12 month interval. When the instrument is due for re­calibration return it to the address above marked for the attention of the
Calibration Department and be sure to include all accessory leads, as these
are part of the calibration procedure.

Correct assembly is shown below. By hanging the instrument round the
neck, both hands will be left free for testing.

KEWTECH

Kewtech Corporation Limited
76 St. Catherine’s Grove
Lincoln LN5 8NA
www.kewtechcorp.com

Distributor

92-1619 04-03