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.
1
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
3
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
8
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.
This manual suits for next models
1
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