What is a Fault Current Calculation (Short Circuit)?

Electricity is inherently dangerous. Have you ever seen a lightning storm? Electrical discharges can create large amounts of energy that can be very damaging. My job, as a professional electrical engineer, is to make sure that every electrical system I design is a safe as possible. While quite rare, there is a phenomenon in electrical systems that can result in what is known as a fault or short circuit. A fault occurs when two or more electrically conducting surfaces (I.E wires, busses etc.) touch something else or each other. The worse fault an electrical system can experience is known as a 3-phase bolted fault. When that occurs the system can generate an extremely large amount of current. When I say large I mean on the order of 10 to 100 times more current than the system would experience under normal operating conditions. The maximum amount of current that a system can experience under this worse case scenario is known as the available fault current (AFC). The AFC of any given system at any given point must take into account a wide variety of variables. For complicated systems software such as SKM Power Tools are used to give an accurate AFC at every panelboard, distribution board, control panel, and service in the system.

Why is this important?

In order to protect equipment, buildings and most importantly people, every electrical system must be designed with the ability to stop, or interrupt, this large amount of electrical current before anything, or anyone, is affected. This is known as the 'Amp Interrupting Current' rating or AIC. As this number is often very large 'Thousand Amp Interrupting Current' or KAIC is often used. The AIC value must be higher than the AFC value. Accurately calculating the AFC will help save the owner money by not over-rating equipment (which can get quite expensive) while still providing a system that is safe to operate and reliable.