What is the difference between short circuit current and fault current

Measure content performance. Develop and improve products. List of Partners vendors. Ground Fault. Short Circuit. Featured Video. Article Sources. The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles.

Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Read More. Your Privacy Rights. To change or withdraw your consent choices for TheSpruce. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data. Short-Circuit Current Rating. The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria.

Also in the NEC , additional equipment, that was often overlooked, was required to be marked with a SCCR shown in black text in table 2. The driving force for adding the marking requirements of SCCR is to ensure the equipment is not installed at locations where the available fault current is higher than its marked SCCR, thus preventing a serious safety hazard. Note that marking for transfer switches is a field marking in addition to the manufacturer marking.

The field marking is needed since the SCCR of the transfer switch can vary based upon the upstream overcurrent protective device type, rating, and settings. Similar to NEC NEC The version of NEC The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit.

This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor s permitted in Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section. Looking at the wording of NEC In the NEC , additional requirements were added that clearly indicate the equipment SCCR must be equal to or greater than the available fault current for industrial control panels and industrial machinery electrical panels and equipment.

In the NEC , similar requirements were added for the equipment shown in red below. In the NEC , the new Section It does serve to highlight the need to evaluate this equipment for proper SCCR to engineers, contractors, and inspectors. It can still be challenging to evaluate and inspect this equipment for proper SCCR because typical circuit breaker panelboards and switchboards will accept numerous different circuit breakers, and the SCCR is dependent on the lowest interrupting rating device installed in the equipment.

Therefore, it is important for engineers and contractors to note the specific circuit breakers and their interrupting ratings so that the inspectors can easily evaluate the equipment for proper SCCR.

It is also important to install circuit breakers with proper interrupting rating when replacing or adding new circuit breakers after the initial installation. If series ratings are used, the series rating must be verified for compliance with Care should be taken to install rejection style clips in equipment that can accommodate Class R fuses, but reject Class H K5 fuses as required per The available fault current is also a key consideration for critical systems where selective coordination is required or desired.

This is because the definition of selective coordination, which was modified in the NEC , now clearly indicates that this includes the full range of overcurrents all currents , from overload to the available fault current, and the full range of overcurrent protective device opening times all times.

Coordination, Selective Selective Coordination. Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the selection and installation of overcurrent protective devices and their ratings or settings for the full range of available overcurrents, from overload to the maximum available fault current, and for the full range of overcurrent protective device opening times associated with those overcurrents.

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