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Operation overview
The KTD40 will test for No-trip loop, High current True Loop Impedance, No-trip PFC/
PSC (Prospective Fault Current), High current PSC using True Loop Impedance, mains
voltage (L-N, L-E and N-E) and correct socket wiring, in addition to the incoming supply
polarity check described on the previous page.
Another unique feature of your KTD40 tester is the high current 2-wire measurement of
the TLI (True Loop Impedance). Regulations and guidance books refer to loop impedance
measurements but up until now loop testers measured loop resistance which is different
from loop impedance, particularly when testing close to the main supply transformer.
This function is therefore recommended when testing for external earth fault loop
impedance (Ze) at distribution boards on non TT systems and similar points on the
supply side of any Switch/RCD gear and when testing the Line/Neutral loop to determine
prospective short circuit current.
It is the variation in power factor that makes the TLI measurement of your KTD40 so
much more accurate than older loop testing techniques. (Because of this there may well
be variations in readings compared to ordinary loop testers or the no-trip function of this
tester, particularly when the measurement is made near to the main supply transformer).
The KTD40 also has a No-trip test mode that is guaranteed not to trip a 30mA or higher
rated RCD providing that the circuit is otherwise healthy.
No-trip vs High current testing
Although the KTD40 High current TLI measurement mode is inherently more accurate
than conventional techniques when measuring close to the main supply transformer, the
difference between resistance and true impedance reduces the further away from the
transformer the measurement is made.
This is why using the No-trip mode is suitable for measurement on final circuits and
similarly remote points. It should be noted however that whilst No-trip testing at these
locations will normally function at a similar high level of accuracy, the low current
measurement technique used is more likely to be adversely affected by external factors
such as contact resistance (e.g. when testing at seldom used socket outlets) and circuit
noise (e.g. switched mode power supply on the same circuit). This can result in the
occasional erroneous reading.
For this reason it is recommended that multiple measurements are made when using the
No-trip mode and any isolated odd results are ignored. When taking multiple readings the
tester or the supply should be powered off between consecutive tests. Where practical
other equipment powered by the same socket should be turned off.
For safety reasons No-trip mode is recommended for all measurements made on TT
systems.
Test lead configuration
Important
The KTD40 can be used with 2 different types of connecting lead. It is important to
understand and use the correct lead configuration for each test mode or you may not
obtain the correct results.
Lead options
1
Ref: KAMP13 The mains lead (IEC C13 to 13A plug) type connector that is
supplied with the tester.
2
Ref: ACC016E The 3-Pole fused distribution board test lead set which terminates
in fused prods/crocodile clips. This is supplied as a separate accessory to the
KTD40.
The lead is an integral part of the tester set-up and should accompany the tester when
being returned for re-calibration or service. Do not use any other type of mains lead or
fused test lead set as it would be likely to give incorrect results.
Lead configuration for No-trip testing
This is the default mode that the KTD40 will start in when turned on. This mode is most
useful for testing at socket outlets, luminaires, wiring terminals, etc. in installations
where the circuit under test may be protected by an RCD.
In No-trip mode the tester can be used with the mains lead when testing at 13A socket
outlets, or the distribution board lead set for testing at other points in the circuit.
When testing with the KTD40 in No-trip mode the 3 colour coded prods/crocodile clips
of the test lead should be connected to the corresponding Line, Neutral and Earth
terminals.
This mode can be re-selected at any time by pressing button 5 labelled ‘No-trip’.
