Safety Alert: Electrical Incidents
Safety Alert No: 44
Date: 18 April 2013
In the last 2 months there has been 3 electrical incidents that has resulted in 3 apprentices receiving electrical shocks or near misses. All three had different root causes and each incident has learning’s that can be taken from them.
During an excavation to expose underground conduits a team found a hard concrete slab around a metre below the surface and under supervision the apprentice utilised a reciprocal saw to cut through the concrete slab. Immediately after commencing the cut an arc occurred indicating that a live HV cable beneath the slab had been cut. In the apprentices interview he stated that the team had not pulled any cables and they believed the conduit was still empty. It would appear that a GPR (Ground Penetrating Radar) was in place and permissions to undertake this work had been approved.
The root cause of this incident was the failure to identify the underground utilities. It is recommended that the identification of utility processes is reinforced with the on-site trades person and apprentices. Pre Job Planning had identified services with in the area of excavation. If underground services are identified during the excavation work the on-site supervisor must be advised and the circuits identified and removed from service.
WHAT IS A GPR?
A Ground Penetrating Radar (GPR) is a geophysical method that uses radar pulses to image the subsurface. This non-destructive method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum and detects the reflected signals from subsurface structures.
The apprentice was sent to carry out a routine “cable test” on HV cables which had recently been installed but not terminated (sticking out of the ground, to the right side of the transformer). The apprentice gained access to the 22Kv dead break elbows and high voltage cable and removed the live red phase cable connection to the transformer bushing, bending the cable back and stepped away to access his test equipment. As the boot returned in close proximity to the HV seat, the 22Kv supply has tracked across causing a significant arc and subsequent release of energy.
The tradesman must identify, isolate, lock-out and attach a danger tag and test the exact task at hand to ensure all cables are de-energised and dead (earthed) with the use of a Modiewark. Appropriate levels of supervision must be given to all apprentices at all times. Apprentices must always apply the “Test Before You Touch” principle to verify de-energisation. Pre job planning should have identified all the live networks within the work area and the site J.S.A. should have listed the live network. Remember - as cable testing requires the removal on the earths and danger tags, constant supervision is required.
WHAT IS A MODIEWARK?
A Modiewark is a non-contact and contact voltage detector, which detects the presence of an alternating electric or electromagnetic field, as a proximity and touch device. Its unique switching action allows for the identification of alternating currents at a distance between 200 mm and 300 mm from a voltage source from 110 volts to 750,000 volts.
While installing light fittings and after turning the lights on the apprentice noticed that one light was not working. The apprentice then proceeded to investigate the cause of the fault and removed the cover of the fitting to check if the light globes were operational. While the apprentice was fault finding his hand touched the light fitting to check and he received and electric shock to his hand. During the investigation it was found that the three pin plug lead had been wired incorrectly at the female plug end. It was established that the active wire had been wired into the earth and the earth into the active.This would have caused the light fitting to become live and as the apprentice touched the light fitting he received an electric shock.
The root cause of this incident is that the tradesman failed to isolate the lighting circuit prior to the apprentice investigating the fault. It is essential that you complete and follow an isolation checklist (IITT)prior to investigating any lighting faults.
Electrical Group Training has a NO WORKING LIVE POLICY. It is a requirement of the employer that all electrical work is carried out using a safe system of work. The safe system of work must include:
1. Follow Isolation Procedures
2. Test Every Time Before You Touch
3. Isolate Where Practical and Shield Exposed Conductor
4. Isolated Circuits