What is Arc Flash?

Arc Flash is when Electricity (Arc) jumps (Flash) from a higher potential (Phase Conductor) to a lower potential (Other Phase Conductor or Ground).  When the Arc Flash happens, there is a large release of energy – mostly thermal.  The energy release is calculated using Fault Current and time, however the Energy Absorbed also uses a distance.  This is measured in Cal/cm2. 

Normally an Arc Flash will happen when switching a Main Switch, Circuit Breaker or Switch-fuse; however this can also happen when wasps make a nest on Transformer Bushings or a possum jumps over a HV insulator causing a short circuit.

Why does Arc Flash need to be considered?

rc Flash needs to be considered on all electrical installations as even low voltages can cause serious Arc Flash damage and burns.  On a typical domestic switchboard, typically there is 5kA fault current, and if the Main Switch fails (or Arc Flashes) when operating without gloves, this can cause 2nd degree (or greater) burns to the hand.

With an opening (or Flash) Time of 0.1 sec for the Service Fuse to blow, and a distance of 50mm from the Arc, this gives an Energy Release of 162J/cm2 or 38.7 cal/cm2.

On commercial or larger installations, fault current is higher however the Main Incomer Circuit Breakers are able to be operated from a further distance.  Even so, if the Fault Current is calculated at 10kA or more or the installation is operating at High Voltage (over 1kV); an Arc Flash Analysis is recommended to be conducted to ensure that PPE with appropriate energy absorption rating is used for Electrical Operators when operating Electrical Infrastructure online.

Other items that need to be considered with Arc Flash is:

– The amount of thermal energy released with an Arc Flash can cause fire, smoke and melt copper.  The molten copper can be atomised and spread out in the vicinity of the Arc Flash due to the pressure wave.  This can cause fires and contamination faults on electrical apparatus if not cleaned properly.

– The pressure wave from the Arc Flash can cause concussion if the operator is within the Arc Flash Boundary.

– Arc Flashes on Transformers can rupture transformer tanks and ignite transformer oil.

How do I reduce Arc Flash in my installation?

There are various ways to reduce the Arc Flash Hazard to personnel and plant.  These include:

Arc Flash Isolation from Personnel – Use Remote Switching from location external to Switchroom.

This removes the Arc Flash hazard from the Electrical Operators as they will be outside the Arc Flash Boundary.

Arc Flash Isolation from Plant – Use Arc Fault Rated Apparatus.

This will contain the Arc Flash and Energy in the Switchboard/MCC.

Reduction in Arc Flash  – Install High Rupture Capacity (HRC) Fuses upstream of the Electrical Apparatus.

HRC Fuses are provide almost instantaneous protection on High Fault Currents.  This will lower the Arc Flash time and therefore Arc Flash Energy.

Arc Flash PPE – Ensure the Electrical Operators wear PPE that is rated to the Arc Flash Energy hazard as determined by the Arc Flash Analysis.

This will reduce the thermal energy absorbed by the skin.

A complete Arc Flash Analysis and Site Inspection will determine the best way to reduce the Arc Flash Hazard on your installation – Call us for assistance.