Engineering and Consulting Services

Short Circuit Study


The installation of electric power systems in buildings brings many conveniences. With the great reliance that we now have on electric power, it is accurate to say that our safety and welfare depend upon its availability. The benefits of having electric power at our disposal are accompanied by a risk: it can also be destructive if not properly controlled. Almost everyone is aware of the possibility of receiving an electric shock; however, not everyone is aware of the thermal and explosive power available from an electric power system if a component of the system fails to perform its intended function. In spite of the disastrous consequences of some system failures, many buildings have been built where these hazards have not been adequately addressed.

Protection
A fuse or a circuit breaker is used in a power system to protect against two kinds of problems: an overload and a short circuit. An overloaded wire can have its insulation destroyed or the high temperature of the wire can cause ignition of flammable materials. This type of failure is almost unheard of today because of the universal application of the requirements of the National Electrical Code in correlating the wire size with the fuse or circuit breaker rating.

A short circuit
The other problem for which a fuse or circuit breaker is intended to protect against is a short circuit. If a short circuit occurs, it almost always involves an electric arc. This is the most likely and violent form of failure and is the most frequently ignored in the design and construction of an electrical distribution system. Powerful explosions can occur in the locations of arcing short circuits. In many of these failures, the electrical equipment can sustain severe damage. In some, additional property loss and loss of life can result.

The study
These hazards are addressed by a short circuit study. If a short circuit were to occur, would the protective devices operate safely, or would they catastrophically fail and cause another location of system failure with attendant arcing and explosive release of heat, smoke and flames?

Is the protective device capable of safely interrupting the flow of an electrical current into a short circuit? This question can only be answered after the magnitude of short circuit current has been determined and compared with the manufacturer's stated interrupting rating.

A short circuit study should be performed during the construction of any new facility to insure that all protective devices are safely applied. In addition, the study should be repeated every 5 to 7 years, since electrical systems and electric utility systems change and may render a one-time safe system, unsafe.