Arc Flash – The Electrician’s Insidious Companion
Published 31 Jul 2019
Blog Written By Patrick Mynett
CEO / High Voltage Specialist at HV Training and Consulting Pty Ltd
Thorne & Derrick International would like to thank Pat Mynett for allowing us to publish his article Arc Flash – The Electrician’s Insidious Companion.
Pat is CEO at HV Training and Consulting Pty Ltd and is a High Voltage Specialist.
In 2014, Pat Mynett decided there was room in the market for another RTO to provide quality electrical training. Especially from a person with recent industry experience, whose main interest was in the electrical safety of workers and the welfare of the plant. Arc flash safety training was a glaring omission in the industry so he developed, wrote and registered a nationally accredited arc flash course for those who work in an arc flash hazard zone.
This is Part 2 in a series of 3 articles about the dangers of arc flash – over the course of these articles we have discussed the definitions, dangers, statistics, causes, prevention and protection against arc flash.
- Introduction to Arc Flash
- Arc Flash – The Electrician’s Insidious Companion
- Overcoming Arc Flash Hazards
The Electrician’s Insidious Companion
Your insidious companion is always lurking there in the background, looking to pounce on people who take short cuts, ignore rules or do not understand how to ban him from the worksite. If your insidious companion pays you a visit you may receive serious burns or pass on to the next world. Do not let this happen to you.
What is an uncontrolled Arc Flash?
A type of electrical explosion that results from a low-impedance (Short Circuit) connection to earth or another voltage phase in an electrical system.
It is the light and heat produced from an electrical arc supplied with Sufficient Electrical Energy to cause fatalities, serious injury, substantial damage, fire, or worse.
What is Sufficient Electrical Energy
In rough figures, a 125kVA transformer 400V (LV) supply would have a fault current capacity of over 3600amps. This just gives an illustration of the current available at the transformer LV terminals.
At the main switchboard this could have dropped considerably, depending on the impedance of the mains, but will always significantly exceed the switchboard load rating.
Padmount transformers can be 20 times the capacity of the above example.
Severity of an arc flash
The severity of an arc flash depends on the amount of fault current available and the duration (Time) the fault is on the system. The system’s voltage is only significant at LV where the volt drop across the arc can be up to 60% of the Low Voltage, so it appears to the protection as a high impedance fault, which therefore clears slowly.
This delay may mean the difference between serious and fatal burns. The careless worker is therefore completely dependent on the distance from and size of, the feeding transformer and most importantly, the switchboard and protection design, commissioning and ongoing maintenance (including tripping batteries) being done correctly.
Energy received from an arc flash
The energy produced by an arc flash and the energy received from an arc flash are two different things. The energy received from an arc flash is measured in Incident Energy (cal/cm2) depends on the distance from the arc flash. The further you are away from the arc flash source the less the incident energy.
What events can cause an arc flash?
An arc flash initiated when the system is static, no movement of system devices. These events can be caused through vermin (rats, mice, etc.) and hot joints. These events generally occur without injury to personnel as no work is being carried out in the vicinity. However, these events can and do cause significant damage to equipment.
An arc flash initiated when there is movement in the system.
The movements can be;
- working live,
- operator error,
- closing, opening and racking of circuit breakers,
- operating switches/isolators live,
- inappropriate operation of switchgear,
- trying to operate damaged switchgear,
- dropping tool/ equipment on live conductors/busbars,
- circumventing interlocks etc.
When arc flash events are due to movement, fatalities or significant injuries can occur, as well as major damage to equipment.
What can you do to protect against an arc flash incident?
- Do not take short cuts!
- Do not work live!
- Do not operate faulty equipment!
- Get an understanding of arc flash, its causes, its hazards and how to mitigate the hazards!
- Know when it is not safe to proceed with the work!
- Know the correct PPE to select and wear!
- Get training in arc flash hazards and mitigation!
Training to recognise Arc Flash Hazards
Now there is training available for people who work at the coal face and operate electrical equipment. This arc flash training imparts the knowledge to recognise, risk assess, mitigate, select the correct PPE for arc flash hazards and know when it is not safe to proceed with the work.
Selecting appropriate PPE
Wearing the correct type of PPE when working in an arc flash environment is imperative. If an arc flash occurs, without PPE you may not go home for a long time or you may not go home at all.
➡ Further Reading
- Arc Flash Clothing & Protection For Safe Windfarm & Wind Turbine Working
- Arc Flash Clothing – PPE To Protect Highways, Street Lighting & Utility Contractors
- Eliminate Arc Flash To Minimise Downtime & Repair Costs At The Circuit Breaker
- Do Insulating Gloves Provide Arc Flash Protection?
- Can Arc Flash Clothing Save Utility Workers Lives?
- Electrical Safety – Arc Flash Accidents & Electrocution In LV-HV Installations
- Arc Flash Calculation – Selecting Clothing & PPE To Protect Lives Against Arc Hazard
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