INSULATION TESTING ON LIVE CIRCUITS – THE SAFE WAY
It’s a familiar scene: An electrician is called out to deal with an electrical fault that’s shut down sections of an installation or, worse, an entire installation. The electrician finds the residual current device (RCD) has tripped and when he closes it, it trips again.
Wayne Ternent, Managing Director at Major Tech, explains, “An RCD senses an imbalance between the phase and neutral currents in the circuits; however, a possible path the leakage current may take is through the phase/earth insulation resistance and, hence an insulation test would be necessary.
“An insulation test to trace the fault would mean separating the various lines and disconnecting appliances from the installation. To minimise downtime on the installation and to reduce the possibility of damage to sensitive electronic equipment, caused by high voltage generated by an insulation tester, the electrician uses a leakage clamp meter,” he says, adding that when it isn’t possible to test a dead circuit to find the problem, this type of meter can be used.
“When measuring the leakage current of two wires – live and neutral – the difference of the current flowing between the incoming wire and the outgoing wire is displayed on the leakage clamp meter,” says Wayne, adding, “Leakages are generally caused by bad insulation on a conductor, or a fault”.
“To avoid nuisance tripping, the earth leakage unit must be temporarily bridged out before the electrician can start to trace the leakage current. To do this, he would start at the earth leakage breaker and work towards the source.”
Wayne explains: “Zero amperage shows that there is no problem. If the supply voltage is 230 V and you get a mA reading, for example, 43.5 mA, this indicates a fault. By using Ohm’s Law, the resistance would be 5.287 kΩ. By measuring this leakage current down the line, the cause of the problem can be isolated.”
Major Tech K2434
Major Tech’s K2434 is the ideal leakage clamp meter to check insulation resistance on live circuits and is stocked by all Major Tech branches. The quality K2434 leakage clamp meter has a measuring range from 0.1 mA to 100 A. Other features include a frequency filter switch to eliminate the effect of harmonics, and data hold.
More info: Werner Grobbelaar on +27 (0)11 872 5500