Safety operations on medium voltage switchgear
Safety operations on medium voltage switchgear (on photo: 12kV medium voltage switchgear; credit:

Hazards of operating on electrical equipment

There are five types of hazards associated with the operation of electrical equipment.

  1. Electrical shock
  2. Electrical burns
  3. Fire and explosion
  4. Heat build up
  5. Mechanical hazards

Electrical shock

There is no way to tell if an electrical conductor or terminal is alive just by looking at it, it should be tested using an appropriate approved tester. Thereafter it should be made safe in such a manner that it cannot be energised by someone else whilst it is being worked on.

Electrical burns

With medium voltage it is not necessary to touch a conductor or terminal in order to get burned. Air does not normally conduct electricity however, when a person gets too close to an electrical wire that is not properly insulated, the air can break down and form a conducting path between them to earth.

Coils and capacitors store electrical energy and release it after power has been turned off and should, therefore, be discharged before work commences.

Fire and explosion

There is great danger of fire and explosion when working with medium voltage equipment, due to the large fault currents that can flow in the system. Oil circuit breakers (OCBs) and oil mini sub stations (MSS) and ring main panels (RMPs) pose a particular threat.

Operator errors can also cause faults, livening up a cable, whist the other end is earthed for instance.

Heat build up

Heat can build up in wires. A lightweight extension lead gets hot when used for heavy duty service.

Avoid using extension leads at all, if possible. If they must be used, ensure they can carry the current without overheating.

Do not string them overhead, across aisles and under mats, where heat can build up and fully extend them.

Mechanical hazards

Electricity is often used to run machinery, rotating machinery and moving parts are always a source of danger, always ensure that guards are in place.

Make sure the machine you are working on cannot be turned on without your knowledge.

Title:Safety operations on medium voltage switchgear by Barry Gass, Alstom Protection and Control
Size:3.5 MB
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Safety operations on medium voltage switchgear
Safety operations on medium voltage switchgear

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  1. […] partly reduced by requiring a switchgear that conforms to all relevant IEC norms as mentioned under design safety. These IEC requirements do ensure that the switchgear is safe in its design, but a part of the risk […]

  2. Karthikeyan
    Jun 15, 2015


    This attached only shows 3 page document, but link shows that 126 page document. I request you that can you please check and confirm.


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