According to the NEC, the fuse should be sized such that it will not blow under normal operating conditions, but will blow in the event of an overcurrent or short circuit. The size and type of OCD required will depend on the size and type of the circuit, as well as the type of load on the circuit.įor example, let's say we are installing a circuit that will be protected by a 50-amp fuse. These devices are designed to interrupt the flow of electricity in the event of an overcurrent (a higher-than-normal flow of electricity) or a short circuit (a direct connection between a hot wire and a neutral or ground wire). In addition to selecting the appropriate size of conductor, the NEC also requires that electrical circuits be protected by overcurrent devices (OCDs), such as fuses or circuit breakers. If the circuit is longer than 100 feet, we would also need to consider the voltage drop, which should not exceed 3% of the voltage of the circuit. According to the NEC, the minimum size conductor for this circuit would be 8 AWG (American Wire Gauge) copper, which has an ampacity of 50 amps in this temperature. The NEC provides tables and formulas to help with this calculation, and it is important to follow these guidelines to ensure the safety and efficiency of the electrical system.įor example, let's say we want to size a conductor for a circuit that will be installed in a room with an ambient temperature of 75 degrees Fahrenheit, and that will be carrying a load of 40 amps. To determine the appropriate size of a conductor, electrical engineers and contractors must consider the ampacity and voltage drop of the conductor, as well as the type of conductor (copper or aluminum), the type of insulation, and the ambient temperature. The ampacity of a conductor is determined by its size and the ambient temperature, while the voltage drop is determined by the length of the conductor and the load on the circuit. Proper cable sizing is important for several reasons, including the prevention of electrical fires, the efficient operation of electrical systems, and the protection of equipment and devices from damage.Īccording to the NEC, the size of a conductor (the wire that carries electricity) should be based on the ampacity (current-carrying capacity) of the conductor, as well as the voltage drop (the loss of voltage along the conductor). One of the key areas covered by the NEC is cable sizing, which refers to the selection of appropriate wire sizes for electrical circuits. The National Electrical Code (NEC) is a set of standards that provide guidelines for the safe installation of electrical systems.
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