10.4.2 Inhibit protective earth confirmation (PE warning)
In some circumstances, you may need to turn off the PE confirmation test inhibit to allow testing to complete a
measurement. The PE warning will still indicate the presence of a PE issue but not stop the test from operating.
10.5 Touch voltage (fault voltage)
For both Loop Impedance and RCD testing the instrument connects a load between the live conductor and the
protective earth (PE) conductor. If the PE conductor is not properly bonded to earth this will cause the voltage on it to
increase, possibly to a dangerous level.
The voltage on the PE conductor is called the touch voltage or fault voltage because anyone touching parts of the
installation or equipment connected to the PE conductor – typically the exposed metal parts – will experience this
voltage.
If the voltage is high enough, they will receive an electric shock. To guard against this, when you start any RCD or
Loop Impedance test, the instrument automatically carries out a touch-voltage check before proceeding.
The touch-voltage check takes only a fraction of a second at the start of the test and is not obvious to the operator.
In the RCD mode the result is displayed in the touch voltage area at the bottom left of the main display area.
In the Loop Impedance mode, the check is not visible, but will inhibit the main testing if hazardous.
If the check shows that the touch voltage is greater than the maximum permissible value, indicating that the
protective conductor is not correctly bonded to earth, testing is inhibited.
If the touch voltage is less than the maximum permitted value, testing proceeds normally. If this voltage is high, but
still below the allowed limit, it is useful to know, as it can indicate a poor earth bond that may require investigation.
The default value for the maximum permitted touch voltage is 50 V, but for special installations such as those in
hospitals and where livestock may be present, this can be changed to 25 V in set up Refer to 15.8.2 Maximum
touch voltage on page 85.
You can also carry out a touch-voltage test on its own in the RCD test options. Refer to 10.5 Touch voltage (fault
voltage) on page 42.
www.megger.com
MFT-X1
42
Live circuit tests
To Next Page
