Loop Test Procedures
Handsfree Loop Testing
The Handsfree feature can be used in either No Trip or high current test modes.
To enable the Handsfree feature simply press ‘Handsfree’ button once, the
‘Handsfree’ annunciator will appear flashing on the display and will continue to do so
until cancelled by a further press of the ‘Handsfree’ button or by changing the
function selector switch.
When the ‘Handsfree’ annunciator is flashing all you need to do is connect the test
lead to a mains supply and the test will be carried out.
High Current Mode
For Ze testing at the distribution board or at any point upstream of RCD protection
there is a traditional fast high current test mode. The high current mode is a 2-wire
test that enables the user to test the true impedance of both the Line-Neutral Loop
and the Line-Earth loop and therefore to establish both the PSC (prospective short
circuit current) and the PFC (prospective fault current) for the installation.
Unlike most testers that only measure the resistance of the Loop, the high current
mode of the Socket & See MFT5000 will measure the impedance of the Loop which
includes an element of reactance. This can be significant where the distribution
board is close to the mains supply transformer and is therefore much more accurate
than older Loop testing techniques.
You should be aware that because of this there may well be variations in reading
compared to ordinary loop testers or to the non-trip function of this tester,
particularly when the measurement is made near to the mains supply transformer.
No Trip Mode
For Zs testing where the circuit being tested is protected by an RCD there is the No
Trip Loop Test mode. In this mode testing can be made at sockets on the final circuit
without fear of tripping the RCD under normal circumstances.
This is achieved by testing at a current that is too low to trip an RCD on an otherwise
healthy circuit. The No Trip test is a 3-wire test that also checks the Live,
Neutral/Earth conductors are correctly connected before running the loop test.
Note- if there is abnormal standing leakage current on the circuit such as a faulty
Microwave Cooker for example then this abnormal leakage is added to low current
used for the above test and the RCD may trip.
However this can be seen as an advantage since it is pointing to a faulty appliance
that should be rectified or replaced.
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