During electrical work, it is likely that electrical covers, escutcheons, etc. will be removed for the purpose of access and workers may touch exposed electrical conductors that may be live. It is important that this work is undertaken by competent and qualified electrical workers.
Whenever undertaking repairs, maintenance or modification of plant and equipment or working on electrical equipment, you could be endangered by its presence or operation, flow of electricity, steam, gas, compressed air, liquids or any others such as gravity and springs. You need to isolate.
Conduct a risk assessment and follow site isolation policy whenever available; otherwise use the following isolation procedures:
General machine isolation
Before commencing work you must shut the equipment down to the level commensurate with the work activity. You must isolate the potential dangers, prevent others from operating the energy source/s by locking out and tagging out (LOTO) the switch or isolating device, and test or check to ensure the lockout has correctly occurred and it is safe for you to proceed. Check for a safe operating procedure (SOP) or safe work practice (SWP) to follow, or use the general steps in machine isolation:
- Consult – with relevant persons regarding knowledge of the process for the shutdown, timing and start-up, and any possible safety, maintenance or production issues
- Identify – the machine, all energy sources and relevant procedures
- Identify – all isolation points / switches
- Controlled shutdown – of the machine and associated lines
- Switch/isolate – the identified circuits/machines
- Secure – secure all isolation points with a lock
- Tag – the switch with a personalised danger tag
- Test – check and verify to prove de-energisation, as appropriate
- Clear – ensure machine is safe before attempting re-start, and
- Test – check and verify by tests to prove energisation, as appropriate.
If the electrical wiring is not to be exposed (i.e. don’t lift electrical covers) then it may not be necessary to undertake electrical testing for full electrical isolation.
Undertake any cleaning and other mechanical maintenance with care and if you are unfamiliar with the work task, or the machine operation do not start work and seek an appropriate work method or training from your supervisor. Stop work and immediately notify your supervisor if you find unprotected or exposed wiring or another workplace hazard.
Rules for testing for de-energised
The industry mantra is TEST EVERY TIME BEFORE YOU TOUCH.
When you isolate you must test for de-energised or test for dead. Testing for de-energised is LIVE WORK because you need to make positive contact with the conductors and there is a possibility that the circuit is energised. You must be licensed and competent; and as a minimum follow the live testing rules. This testing requires a SWMS and a risk assessment to be conducted. You may also need to have a trained and competent Safety Observer.
The test for de-energised must make positive contact with the conductors and you must check your test instruments both before and after testing.
Note: Proximity sensors are non-contact indicators and must not to be used to prove isolation. They can be useful to detect electrical signals but are not a reliable confirmation of safe de-energisation or isolation.
Electrical isolation
Steps in low voltage electrical isolation are:
Consult/warn, Identify, Switch/isolate, Secure/LOTO and Test to confirm de-energised.
Following isolation of all power sources, and the locking out of all isolators, and tagging of each by all persons required to work on or near the electrical equipment, test to ensure it is safe to proceed before commencing work.
- A padlock is to be used to lock out switches and circuit breakers on electrical circuits or equipment to enable work to be carried out, on or adjacent to such equipment.
- If more than one person is working on the same de-energised electrical installation, individuals should ensure their own personal lock is applied to the isolation point, otherwise the principles of tagging apply. This includes apprentices as well. Danger tags must be securely attached to the isolator/control switch or device so there is no risk of becoming dislodged. They must be clearly visible to ensure inadvertent restoration of the power does not occur.
- Each person is to be fully informed as to the extent of such isolation and must also be advised of specific areas or items of equipment that are not de-energised, if any.
You must be absolutely certain that the fuse-switch or circuit breaker that you have locked and tagged is the correct one. If you are in any doubt as to which switches must be isolated, do not proceed until you have confirmed from schematics or tracing or asked your Supervisor or appropriate person.
Never assume an exposed conductor is dead – TEST EVERY TIME BEFORE YOU TOUCH.
Danger tags and personal locks
A danger tag is used at all points of isolation to identify that the energy sources are isolated. However, the danger tag is not required when using dedicated personal isolation locks that are labelled with the owners name and contact number. Each Danger Tag or lock should be:
- Be red, white and black in colour and have ‘Danger’ clearly displayed.
- an approved type in new condition, without erasures or alterations and should bear the contractor’s name
- dated and signed by the worker or workers involved in carrying out the work or, where appropriate, by the supervisor in charge of the workers
securely attached in a prominent position on each isolation point (i.e. the point or many points used to isolate electrical parts) or device.
If you are working alone and the job is incomplete at the end of the work period, you should remove your Danger Tag (or personal lock) and replace it with an “Out Of Service” Warning Tag.
“Out Of Service” Warning tags can also be used to quarantine equipment found to be non-compliant, in disrepair, or otherwise unsuitable. The tag needs to be labelled clearly indicating the issue, include the date, person, and a traceable record to identify the issue.
Personal Danger Tags should not be left on site. When a worker leaves for the day they should remove their danger tag and if no one else has a tag in place, replace it with an out of service tag. When the worker returns to site they replace the out of service tag with their danger tag again. Therefore there should not be an occurrence when you need to remove another person’s danger tag.
Remember Life Saving Rule #3
I will never remove another person’s Danger tag without written authorisation
In exceptional circumstances, a responsible management person may remove the tag, only after making certain they know the reasons for the tag being attached and after a thorough inspection, checks and tests to make sure it is safe to restore power.
Disconnect and tying-back
In certain situations (e.g. when removing wiring such as in a strip out or demolition) it may be more practical to secure the isolation by physical disconnection and tying back the cabling at the source, thus isolating the worksite. Confirm isolation by tagging and testing.
Bonding of conductors
Otherwise known as the “Strip, Twist and Tape” method. Temporary bonding (that is, short-circuiting the earth to the neutral and with the de-energised phases) should be used where there are cables left un-terminated for any period of time. This will prevent accidental re-energisation of circuits when fit off has not been completed.
This is also required when working with HV equipment. PPE and safety apparel should be used when attaching or removing temporary HV bonding conductors.
- Attaching – first connect the temporary bonding conductors to the general earth, then neutral, before any attempt is made to attach them to any de-energised component portion of the electrical installation.
- Removal of the bonding conductors must be carried out in the reverse order (ie remove the temporary bonding conductors first from each of the de-energised phases, then neutral, then earth).