Short Circuit Current
The National Electrical Code stipulates that equipment like fuses and
circuit breakers intended to break current at fault levels shall have an
interrupting rating sufficient for the system voltage and current which is
available at the line side terminals of the equipment. See NEC 110-9
Further that service equipment shall be suitable for the short circuit
current available at its supply terminals.
The intent of these sections is to require the use of equipment which is so
designed for its installation location that when a short circuit condition
exists, neither the overcurrent protection device with an appropriate current
limiting ability or other circuit components will be damaged.
Therefore the specifications of current limiting overcurrent protection is
an essential consideration when designing, specifying, and installing electrical
The calculation to arrive at available short circuit current for a specific
installation is now typically required to be submitted with a riser diagram when
a service change or installation is to be made.
The method shown here is referred to as the point-to-point method. There are
others to include an Omic Method, a Per-Unit Method, TRON registered trademark
Computer Software Method. All are to arrive at I s.c. sym RMS available short
circuit symmetrical RMS current at the point of fault.
Click HERE to
see the entire Cooper Bussmann pdf file booklet which explains this point to
point method as well as all other methods..
Find a request for information form letter HERE.
Find the worksheet to make a calculation HERE.
Find check values for this calculation HERE.
Find a table with values for C HERE.
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