Earth Fault Loop Impedance (Zs) - Testing 16 Amp Industrial Socket Outlets Both Single and 3 Phase Electrician Matt is carrying out an earth fault loop impedance testing (sometimes called the Zs test) on a 16 amp single phase and a 16 amp 3 phase industrial socket outlet (sometimes call a commando socket). This video Matt shows how to carry out the tests as well as the plugs and leads Matt has made up to make this test easier but your thoughts on if it’s safer are VERY welcome... As always prepa