When measuring low Zs values, does your meter lie?
Bill Allan from NAPIT writes about the measurement of low Zs Values and gives some great advice from measuring Zs on large cables to the formula for the earth fault loop impedance.
When Your Meter Lies To You
(Measuring Low Zs Values)
by
Bill Allan
Introduction
Knowledge of the earth fault loop impedance (Zs ) is an essential factor where the most commonly used protective measure - automatic disconnection of the supply – is used (Fig. 1).
Fig 1 Earth fault loop impedance path