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Arc flash incident, bad racking?

There are many reasons causes arc flash incidents. Some of arc flash explosions occur when substation personnel insert or remove (rack in or out) circuit breakers from low or high voltage switchgear cubicles. Manual racking in and racking out circuit breakers poses potentially lethal arc flash exposure.

Assumptions and complacency are two of electrical safety‘s worst enemies. If the following story hits uncomfortably close to home for you, it will have served its purpose.

In January 1993, two employees were killed and three were seriously injured by an electrical arc flash at a Texas power station.

The dead employee (not confirmed) had racked-in a circuit breaker and sent the close command, but the breaker failed to close. With the breaker indicator showing that it was still open, the operator began racking-out the breaker to troubleshoot the problem with his supervisor looking on. Neither knew that the breaker had received the close command. The breaker had unlatched and begun to close, but the mechanical problem prevented it from completing the operation.

As a consequence, the operator attempted to rack out the circuit breaker even as it was receiving a close command. When he was finally able to move the breaker, the mechanical bind was relieved and the breaker closed while it was partially racked-out. The result was an electrical arc flash and explosion that critically burned the operator and the supervisor and slammed them into the wall. Both were killed.

The arc flash then travelled around a corner and burned three other workers. All of this carnage occurred within milliseconds.

Download PDF guides on arch flash protection and assesment (from cablejoints.co.uk):

Reference: Ben Johnson and Jack Wells – Steering Committee Cochairs – IEEE/NFPA Collaboration on Arc Flash Occurence, Feb 2007


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Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears. Professional in AutoCAD programming and web-design. Present on Google+.



8 Comments


  1. Amitabh C
    May 18, 2014

    Never rack out a breaker unless isolators are open.

  2. [...] the power network where transmission lines and distribution feeders are connected together through circuit breakers or switches via busbars and transformers. This allows for the control of power flows in the network [...]

  3. [...] voltage (4.16 kV through 34.5 kV) power distribution systems. One is metal-clad switchgear using draw-out air-magnetic or vacuum circuit breakers and relays for both load switching and fault protection: [...]

  4. [...] In addition to the 94/9/EC Directive, which regulates how explosion protected equipment and protective systems are placed on the market and the design, construction [...]


    • Edvard
      Dec 09, 2011

      Thank you very muh Roya! This racking device is for Masterpact circuit breakers – low voltage.

  5. [...] Safety of personnel in the vicinity of a GIL is very high because the solid metallic enclosure provides reliable protection. Even in the rare case of an internal failure, the metallic enclosure [...]

  6. [...] Electrical safety – Whilst awareness of the dangers of arc flash has continued to increase over the last few years, the number of incidents that are still occurring [...]

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