Check out this short case-study on electrical testing in Otahuhu which found a potentially hazardous, badly installed, circuit.

“Earth Fault Loop Impedance testing a 10 amp power point circuit extension!”

You say what? Don’t you love it when tradies talk acronyms in front of customers. BullSh#t baffles brains some say.

So, let’s break this down for you and take the bull out of the sh#t.

Main reason why this test is conducted is to ensure the following;

1. Will the circuit breaker or fuse trip/blow and clear the fault?
2. Will the circuit breaker or fuse trip/blow in time?

Failure to do this test on active power circuits before extending and or modifying the circuit could potentially lead to property damage though fires or electrocution due to the circuit breaker not tripping/blowing due to incorrect cable sizes suppling the power circuit over a long distance.

Results of Testing

Result of the test conducted for Otahuhu Business Association (OBA) required an extension to the power circuit to supply interactive display board.

On investigation the cable sizing was 2.5mm two core plus earth tough plastic sheath known to us sparkles as a 2.5mm 2C+E CU TPS.

Testing was conducted using a Calbrated Fluke 1664 Multifunction Tester using the meter set on Z Ohms Loop Impedance test. The following results were obtained 1.72 ohms @ 135 amps on a 79 meter cable run on a C16A miniature circuit breaker.

Looking in to the ASNZS 3000 Section 8 Table 8.2 revealed this had failed to pass the test. Maximum allowed ohms was 1.22 ohms Rphe for this circuit.

Further Investigation required to ensure an OME install could proceed found the first 40 meters of the circuit was in 1.5mm 2C+E TPS surface mounted in conduit and the remaining 39 meters in 2.5mm 2C+E.

Our Customer was informed of this predicament because OME could not proceed with the installation as the previous electricians work was not compliant.

After discussion with OBA, OME supplied a solution running 1x 10mm Red and Black and 1x 4mm Yellow /Green copper cables the full length of the cable run in 25mm plastic conduit, tapping of one 10A Double power point at 40 meters and running to the original power point 79 meters away from the main switchboard.

Result of Testing after the upgrade/rectification