Kewtech KT41 User manual

KEWTECH
KT41/KT42 digital multi function testers
Instruction manual

Contents
1 Safety Notice 1
2Features and Principles of Measurement 3
3 Specifications 9
4Instrument layout 12
5Operating instructions 14
6Servicing & Calibration 18
The KT42 incorporates Anti Trip Technology (ATT) which
electronically by-passes most passive RCDs at
Distribution Boards. This saves time and money by not
having to take the RCD out of circuit during testing and
is a safer procedure to follow.
The ATT circuits may not by-pass some RCDs and this
will result in the RCD tripping out as they would with a
conventional loop tester. Also, in the case of high sensi-
tivity RCDs rated at 10mA or less the ATT circuits may
not function. If there is doubt as to whether this tester
will by-pass a particular RCD, contact Kewtech with
details of manufacturer, model no., rating and sensitivity.
Please read this instruction manual carefully before using
this tester.

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1 Safety Notice
Electricity can cause severe injuries even with low voltages
or currents. Therefore it is extremely important that you
read the following information before using this Tester.
1.1 This instrument must only be used by a competent trained
person and in strict accordance with the instructions.
Kewtech will not accept liability for any damage or injury
caused by misuse or non-compliance with instructions or
safety procedures.
1.2 This instrument is only intended for single phase operation,
230V AC+10%-15% phase to earth or phase to neutral
operation. It must never be connected phase to phase -
damage will result.
1.3 When conducting a test, particularly on earth spikes, do
not touch any exposed metal work. This is because the
earth has a current flowing through it for the duration of
the test (approx.) 20ms).
1.4 Never open the instrument case - there are dangerous
voltages present. Only trained, competent Electronic
engineers should open the case. Send the unit to Kewtech
if a fault develops.
1.5 This instrument is primarily protected by HRC Ceramic
fuses. Do not attempt to replace them if they fail. If they
do contact Kewtech.
1.6 If the overheat symbol appears in the display disconnect
the instrument from the mains and allow to cool down.
1.7 When using the KT41 all RCDs in the circuit must be by-
passed for the duration of the test. Do not operate the
RCD Test button with the RCD by-passed.
1.8 This unit is designed to give minimum ‘splash’ when
connecting to an earth point when using the external earth
probe. To reduce the effect further, always connect the

2
probe in a firm and positive manner. The external earth
probe, when used, should always be considered and
treated as a hazardous live part.
1.9 External earth probe. The tip is at mains potential (low
current). Be careful to keep your hands behind the finger
guard and make a firm and positive contact with the sur-
face to be tested. Always keep your hands and fingers
behind all finger guards on test leads with this meter.
1.10 Always inspect your Insulation Tester and test leads before
use for any sign of abnormality or damage. If any abnormal
conditions exist (broken test leads, cracked case, display
faulty, inconsistent readings, etc) do not attempt to take
any measurements. Return to Kewtech for rectification.
1.11 This meter has been designed with your safety in mind.
However, no design can completely protect against incor-
rect use. Electrical circuits can be dangerous and/or lethal
when a lack of caution or poor safety practice is used. Use
caution in the presence of voltages above 50V as these
pose a shock hazard.
1.12 Pay attention to cautions and warnings which will inform
you of potentially dangerous procedures.
1.13 If at anytime during testing there is a momentary degrada--
tion of reading, this may be due to excessive transients or
discharges on the system or local area. Should this be
observed, the test should be repeated to obtain a correct
reading. If in doubt always contact Kewtech.
1.14 Never assume an installation circuit is not live. Confirm it
is de- energised before commencing testing.
1.15 Replace worn and/or damaged leads with new ones
approved by Kewtech immediately. Only use accessories
recommended by Kewtech as they are designed to work
with the tester. The use of any other items is prohibited as

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they may not have the same safety features built in.
1.16User of this equipment and/or their employers are
reminded that Health and Safety Legislation require 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 from inadvertent short circuits.
Where the assessments show that the risk is significant
then the use of fused test leads constructed in accordance
with HSE guidance note GS38 Electrical test Equipment for
use by Electricians should be used.
2Features and Principles of Measurement
2-1 Features
▲KT42 with ATT avoids the need to by-pass most passive
RCDs
▲Large high contrast display
▲Auto lock out if test resistor overheats
▲Voltage indication
▲Microprocessor controlled
▲Measures PSC
▲Measure low loop with 0.01Ωresolution
▲High loop ranges permit measurement of ground spikes
▲Bright colour coded LED mains status indicators
▲Distribution board lead included as standard
2-2 Principles of Measurement (Fault Loop Impedance)
If an electrical installation is protected by over-current protec-
tive devices including circuit breakers or fuses, the earth loop
impedance should be measured.
In the event of a fault the earth fault loop impedance should be
low enough (and the prospective fault current high enough) to

4
allow automatic disconnection of the electrical supply by the
circuit protection device within a prescribed time interval.
Every circuit must be tested to ensure that the earth fault loop
impedance value does not exceed that specified or appropriate
for the over-current protective device installed in the circuit.
For a TT system the earth fault loop impedance is the sum of
the following impedances;
Impedance of the power transformer secondary winding.
Impedance of the phase conductor resistance from the
power transformer to the location of the fault.
The impedance of the protective conductor from the fault
location to the earth system.
Resistance of the local earth system (R).
Resistance of the power transformer earth system (Ro).
For TN systems the earth fault loop impedance is the sum of
the following impedances.
Impedance of the power transformer secondary winding.
Impedance of the phase conductor from the power
transformer to the location of the fault.
Impedance of the protective conductor from the fault
location to the power transformer.

5
In accordance with the international standard IEC 60364 for a
TT system the following condition shall be fulfiled for each cir-
cuit.
RAmust be ≤50/la where;
RAis the sum of the resistances of the local earth system R and
the protective conductor connecting it to the exposed conduc-
tor part. 50V is the maximum voltage limit (it may be 25V in
certain circumstances). Ia is the value of current that causes
automatic disconnection of the protective device within 5 sec-
onds.
When the protective device is a residual device (RCD), Ia is the
rated residual operating current I n. For example in a TT sys-
tem protected by an RCD the maximum RAvalues are as fol-
lows:
Rated residual
operating cur- 10 30 100 300 300 1000
rent I n mA
Ra (at 50V)Ω5000 1667 500 167 100 50
Ra (at 25V)Ω2500 833 250 83 50 25

6
For this example the maximum value is 1667Ω, the loop tester
reads 12.74Ωand consequently the condition RAis ≤50/Ia is
met. It is also important to test the operation of the RCD using
a dedicated RCD tester in accordance with the international
standard IEC60364 for a TN system. The following condition
shall be fulfiled for each circuit.
Zs≤Uo/Ia where Zs is the earth fault loop impedance voltage is
the nominal voltage between phase and earth and Ia is the cur-
rent that causes the automatic disconnection of the protective
device within the time stated in the following table.
Note:
When the protective device is a residual current device
(RCD), Ia is the rated residual operating current 1 n. For
instance ina TN system with a nominal mains voltage of Uo
= 230V protected by type gG fuses the Ia and maximum
Zs values could be:
Uo (Volts T (seconds)
120 0.8
230 0.4
400 0.2
>400 0.1

7
If the prospective fault current is measured, its value must be
higher than the Ia value of the protective device concerned.
The maximum value of Zs for this example is 2.1Ω(16 amp gG
fuse, 0.4 seconds). The loop tester reads 1.14Ωand conse-
quently the condition Zs≤Uo/Ia is met.
Rating Disconnecting time 5s Disconnecting time 4s
(A) Ia (A) Zs (Ω)Ia (A) Zs (Ω)
6288.2 47 4.9
10 46 5 82 2.8
16 65 3.6 110 2.1
20 85 2.7 147 1.56
25 110 2.1 183 1.25
32 150 1.53 275 0.83
40 190 1.21 320 0.72
50 250 0.92 470 0.49
63 320 0.71 550 0.42
80 425 0.54 840 0.27
100 580 0.39 1020 0.22

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2.3 Principles of the measurement of line impedance and
prospective short circuit current
Line impedance on a single phase system is the impedance
measured between phase and neutral terminals.
Measurement principles for line impedance are exactly the
same as for earth fault loop impedance measurement with the
exception that the measurement is carried out between phase
and neutral.
The protective 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 volt-
age and the impedance of the path taken by the fault current.
Measurement of prospective short circuit current can be used
to check that the protective devices within the system will
operate within safety limits and in accordance with the safe
design of the installation. The breaking current capacity of any
installed protective device should be always higher than the
prospective short circuit current.

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3 Specifications
Measurement specification
Loop impedance
Prospective Short-circuit Current
Voltage
Reference conditions
Ambient temperature: 23±5˚C
Relative humidity: 60±15%
Nominal system voltage
and frequency: 230V, 50Hz
Altitude: Less than 2000m
Measuring Nominal test Intrinsic
Range range current at 0Ωexternal accuracy
loop/Period applied
20Ω0.00-19.99Ω25A/20ms
200Ω0.0-199.9Ω2.3/40ms ±(2%rdg+3dgt)
2000Ω0-1999Ω15mA/280ms
Measuring Nominal test Intrinsic
Range range current at 0Ωexternal accuracy
loop/Period applied
200A 0.0-19.99A 2.3A/40ms
2000A 0-1999 25A/20ms
20kA 0.00-4.00kA 25A/20ms
PSC accuracy is
derived from the
loop impedance
accuracy
Measuring range Intrinsic accuracy
180-260V ±(2%rdg+2dgt)

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Operating error
Loop impedance
The influencing variations used for calculating the Operating
error are:
Ambient temperature: 0˚ and 35˚C
Phase angle: 0˚ to 18˚
System frequency: 49.5Hz to 50.5Hz
System voltage: 195V to 253V
General specification
Storage temperature: -5˚C to 60˚C
Storage humidity: 85% maximum
Dimensions: 175 x 115 x 85.7mm
Weight: KT41 - 500g
KT42 - 700g
Maximum altitude: 2000m
Over range indication: ‘OL’
Input voltage greater
than 260V indication: ‘VP-E Hi’
Over temperature
indication
Applied standards
Instrument operating standard IEC/EN61557-1
IEC/EN61557-3
Range Operating range compliant
with EN61557-3 operating error
20Ω0.35 to 19.99Ω
200Ω20.0 to 199.9Ω
2000Ω200 to 1999Ω

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Safety standard IEC/EN 61010-1, CATIII (300V)
instrument
Protection degree IEC 60529 (IP40)
Accessories
KAMP10UK, ACC016E, ACCEP5 mains test lead with IEC
Connector
SLP5 Earth probe
SL16E Distribution board fused test lead
(Fuse: 10A/600V fast acting ceramic)
Test lead carry pouch
Model KT42 KT41
Anti trip technology* ✓X
Loop 0-19.99Ω/ 0-199.9Ω/0-1999Ω✓✓
PSC 0-199.9A/ 0-1999A/0-4.00kA ✓✓
Mains Lead for Sockets KAMP10UK ✓✓
ACC016E ACCEP5
External Earth Probe SLP5 ✓✓
Distribution Board Lead SL16E ✓✓
*ATT does not operate on the 2000Ωranges
This manual and product may use the following symbols
adopted from International Safety Standards;
Equipment protected throughout by DOUBLE
INSULATION or REINFORCED INSULATION;
Caution; risk of electric shock;
Caution (refer to accompanying documents)

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4Instrument layout
LCD display
Test button
Main status
indication
LED
Range switch

13
Test leads
LCD display
ACCEP5 ACC016E
KAMP10UK

14
5Operating Instructions
5.1 Initial Checks: to be carried out before any testing;
Always inspect your test instrument and lead accessories
for abnormality or damage-
If abnormal conditions exist DO NOT PROCEED WITH
TESTING. Have the instrument checked by Kewtech.
Before pressing the test button, always check the LED's for
the following sequence:
P-E Green LED must be ON
P-N Green LED must be ON
Red LED must be OFF
If the above sequence is NOT displayed or the RED LED is
on for any reason, DO NOT PROCEED AS THERE IS
INCORRECT WIRING. The cause of the fault must be
investigated and rectified.
Voltage Measurement
When the instrument is first connected to the system, it
will display the phase-earth voltage which is updated every
1s. This mode is cancelled the first time the test button is
pressed. If this voltage is not normal or as expected, DO
NOT PROCEED.
NOTE: This is a single phase (230V AC) instrument and
under no circumstances should it be connected to 2-
phases or a voltage exceeding 230VAC+10%-15%.
If the input voltage is greater than 260V the display will
indicate ‘VP-E Hi’ and Loop or PSC measurements can not
be made even if the Test button is pressed.
5.2 Measurement of Loop impedance
a. Loop Impedance at Mains Socket Outlet
Select the 20Ω, 200Ωor 2000Ωrange as desired

15
Connect the mains lead to the IEC socket of the
instrument
Plug the moulded plug of the mains lead into the
socket to be tested
Carry out the initial checks
Press the test button. A beep will sound as the test is
conducted and the value of loop impedance will be
displayed
Wait for the display to indicate the input voltage
before conducting another test or before
disconnecting the instrument from the socket
If the display shows ‘OL’ then this usually means the value mea-
sured exceeds the range selected, e.g. if the 20Ωrange was
selected then the loop impedance is greater than 19.99Ωand
you must switch up a range to the 200Ωrange.
5.2.1 External Earth Probe
The phase-earth loop impedance of exposed metal
work (e-g. pipes/conduit etc.) can be tested using the
external earth probe.
Connect the unit to the socket as normal. Plug the
external earth probe into the instrument external
earth probe socket, ensuring the probe is held with
fingers behind the finger guard. This will break the
earth continuity at the socket and the red LED will
switch on. The point at which the probe is now
connected becomes the new earth point instead of at
the socket. When the probe is placed in contact with
the earthed surface to be measured, the LED mains
status should revert to the correct sequence described
in initial checks. When this happens, press the test
button to measure the loop impedance.

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bLoop impedance at the distribution board
Warning: never connect 2 phases to this instrument
Select the 20Ω, 200Ωor 2000Ωrange as required
Connect the distribution board lead model ACC016E
to the IEC socket on the instrument
Connect the red phase lead of the ACC016E to 1
phase of the distribution board, the black neutral lead
to the neutral of the distribution board and the green
crocodile clip to the earth
Carry out the initial checks
Press the test button. A beep will sound as the test is
conducted and the value of loop impedance will be
displayed
Wait for the display to indicate the input voltage before
conducting another test or disconnecting from the
distribution board. When disconnecting from the
distribution board, it is good practice to disconnect the
phase first
cLoop impedance at 3-phase equipment
Use the same procedure as (b) ensuring only 1-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.
d. The ACC016E can also be used for testing at
luminaires
Testing as described in (a), (b), (c) and (d) will measure the
Phase-Earth loop impedance. If you wish to measure the Phase-
Neutral loop impedance in items (b), (c), (d), then same proce-
dure should be followed except the earth clip should be con-

17
nected 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. same point as the green earth
clip. This will only work if there is no RCD in this type of sys-
tem.
5.3 Measurement of PSC (Prospective Short Circuit Current)
Warning: Never connect 2 phases to this instrument
This is normally measured at the distribution board between
the phase and neutral.
Select the 20kA, 2000A or 200A range
Connect the ACC016E distribution board lead to the IEC
socket on the instrument
Connect the red phase probe of the ACC016E 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
Carry out the initial checks
Press the test button. A bleep will sound as the test is
conducted and the value of PSC will be displayed
Wait for the display to indicate the input voltage 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 that 5A
approx.) it is not possible to obtain an accurate PSC reading
and the unit will lock out the PSC range by displaying the VN-E
Hi over-range symbol.
PSC funcyion has a power factor correction of 0.84.
PSC = Vx 0.84
A
If the PSC ranges are selected whilst connected to a socket

18
outlet via the mains lead KAMP10UK, a test will take place
between Phase and Earth due to the fixed wiring of the mould-
ed mains plug i.e. a Phase-Earth fault current test.
5.4 General
5.4.1 If the symbol appears, this means that the test
resistor is too hot and the automatic cut out circuits have
operated. Allow the instrument to cool down before
proceeding. The overheat circuits protect the test resistor
against heat damage.
5.4.2 The test button may be turned clockwise to lock it down.
In this auto mode, when using distribution board lead
ACC016E, tests are conducted by simply disconnecting and
reconnecting the red phase prod of the ACC016E avoiding
the need to physically press the test button i.e. ‘hands free’
6 Servicing and Calibration
If this tester should fail to operate correctly, return it to
Kewtech marked for the attention of the Service Department.
stating exact nature of fault. Make sure that:
a. operating instructions have been followed
b. leads have been inspected
c. the unit is returned with all accessories
Regular re-calibration is recommended for this instrument. We
recommend that with normal use, the instrument is calibrated
at least once in every 12 month interval. When this is due for
re-calibration return it to Kewtech marked for the attention of
the Calibration Department and be sure to include all accessory
leads, as they are part of the calibration procedure.
The mains lead supplied with this instrument (model
KAMP10UK) for testing at sockets is part of the instrument. It