Arc Protection System

An arc protection system is made up of a trip relay, sensors and an arc quenching device. Arc protection systems are hugely important, as arc flash accidents occur approximately 8 to 10 times each week in the UK. Unfortunately, many switchgears are left without arc flash protection, despite its common occurrence and destructive potential.


What is an arc flash?

An arc flash is one of the most destructive electrical faults possible to have. Not only will it cause tremendous damage to equipment, but could also give life changing and even life-threatening injuries to any personnel within a close proximity. See more here.

PPE is essential in helping to protect employees against arc flashes. Reputable arc flash PPE suppliers, such as Tower Supplies will ensure your employees have the level of protection they need.


What is the NFPA 70E and where does it apply?

The NFPA 70E addresses employee workplace electrical safety requirements.

It defines work practices that protect workers from electrical hazards, including arc flashes, during the inspection, operation and maintenance of electrical equipment.

The NFPA 70E standard covers most workplace activities related to electrical energy or equipment. The major exceptions are:

  • Vehicles; such as ships, aircraft and railways
  • Communications equipment under the exclusive control of communications utilities.
  • Certain electrical installations under the exclusive control of an electric utility.

How to calculate arc flash rating

As part of NFPA 70E, an arc flash hazard analysis should be done in order to protect personnel from the possibility of being injured by an arc flash.

There are two distinct mathematical methods of calculating the available arc flash energy present at a specific piece of equipment.


Why do I need an arc protection system?

8 to 10 arc flashes occur in the UK every week. Without arc protection in place, the consequences can be very serious.


What does an arc protection system look like?

You only need three components to create a reliable arc protection system:

Arc protection system

Why do I need arc protection?

There are many benefits to fitting arc fault protection:

  • Damage limitation – Due to an ultra-fast tripping time of 2ms and quenching time of just 3ms, total destruction on the switchgear is prevented and is limited to only one section. This saves a great deal of downtime, because it won’t be necessary to wait for a whole board to be rebuilt. Selective tripping is also an option, meaning only the circuit breaker closest to the fault will trip. This can also assist in finding the source of the fault during investigation.
  • Cost-savings – There are many costs to consider in the aftermath of an arc fault. This includes an expensive rebuild of the switchgear, along with the repair of any other damage done to the room and the labour costs for doing so. Other costs often not considered are those when a staff member is injured (or worse) in the blast. This may involve legal fees, fines and compensation.


Video: Arc protection system configuration

This short animation shows a basic configuration setup of an arc protection system (without a quencher). This Arcteq system features an AQ110 and 3 AQ101 relays, along with several point sensors. This comprehensive setup will allow for rapid arc detection (just 2 ms). The quick tripping of the circuit breaker will result in less damage from the arc to both equipment and personnel working nearby because it cannot reach full velocity.


It is vital the relay works very quickly because it only takes 300ms for an arc flash to reach maximum velocity.
Here you can see how the severity increases over a short amount of time:

10-30ms (Compression stage). Ignition of current flow through ionised air.
Rapid release of energy.
Maximum pressure.
30-50ms (Expansion stage). Shock/pressure wave (up to 4 bars).
Sound wave.
50-100ms (Emission stage). 20,000°c temperatures.
100-300ms (Thermal or ‘burn through’ stage). Toxic gases.
Steel and copper fire.
Hot shrapnel.


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