NEC Article 100 - Branch Circuit Definition



Again, we will explain more important definitions included in NEC code Article 100 which will be used along this Course, toady we will show the term “Branch Circuit “Definition.


Branch Circuit: see fig.1




A branch circuit is a portion of a wiring system that extends beyond the final, automatic overcurrent protective device (i.e., fuse or breaker) which qualifies for use as branch-circuit protection, and terminates at the utilization device or outlet (such as a lighting fixture, motor, or heater). 

fig(1): Branch circuit definition

Thermal cutouts , motor overload devices and fuses in luminaires or in plug connections, which are used for ballast protection or individual fixture protection, are supplementary overcurrent protection on the load side of outlet and is not required by the Code, nor a substitute for the Code-required branch-circuit protection and does not establish the point of origin of a branch circuit. 


Branch Circuit, Appliance:see fig.2

fig(2): Branch circuit, Appliance

The point of differentiation between “appliance” branch-circuits and “general” branch-circuits is related to what is actually connected. For a circuit to be considered an “appliance” branch circuit, it may not supply any lighting, unless that lighting is part of an appliance. 





Branch Circuit, General Purpose: 
see fig.2


Such circuits are identified by the fact that they supply two or more outlets for receptacles, lighting, or appliances. 

Notes:
The circuit voltage in case of Appliance branch circuit has no limits but for general purpose branch circuit it will be limited to:


  • 150 V to ground for circuits supplying lamp holders, fixtures or receptacles of standard 15 Amp rating. 
  • 300 V to ground for circuits supplying fluorescent, incandescent or mercury lighting under certain conditions. 
  • 600 V for ungrounded circuits supplying electric discharge lighting 


Branch Circuit, Individual:
see fig.3


fig(3): Branch circuit, Individual

It is a branch circuit supplies a single or “individual” piece of equipment. Circuit supplying both halves of a duplex receptacle is not an individual branch circuit in most cases, because each half of the duplex is classified as a separate device. 


Branch Circuit, Multiwire:
see fig.4 &5


fig(4): Branch circuit, Multiwire


It is defined as a branch circuit that consists of two or more ungrounded conductors (two or more "hot" wires) that have a voltage between them (they are not on the same electrical phase and so are connected to different buses in the electrical panel), and a grounded conductor (the neutral wire) that has equal voltage between it and each ungrounded conductor (hot wire) of the circuit and that is connected to the neutral or grounded conductor of the system.



fig(5): Branch circuit, Non-Multiwire

A 3-wire, 3-phase circuit (without a neutral or grounded conductor)(see fig.5) ungrounded delta system is not a “multiwire branch circuit,” even though it does consist of “multi” wires, simply because there is no “neutral” or other grounded conductor.

Remember, such a circuit must, by definition, also contain a “grounded” conductor, which may be a neutral, as in the typical 3-phase, 4-wire systems, or a grounded phase conductor, such as in a “corner-grounded” delta system. 



Branch Circuit Overcurrent Device:
see fig.6

These are devices capable of providing protection over the full range of overcurrents between the device rating and its interrupting rating, but never less than 5000 A.


fig(6): Branch circuit Overcurrent Device


They are far more robust than the supplementary overcurrent protective devices that offer limited protection for certain applications such as limiting the amount of energy that could enter a luminaire.



In the next topic, I will continue explaining other definitions from article 100.

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