A branch circuit consists of the conductors between the final overcurrent protection device (OCPD) and the point of use outlets [Art. 100] (Fig. 1). Article 210 contains requirements for installing these circuits.
Specific-purpose branch circuits (identified in Table 210.2) have additional requirements [210.2]. These amend or supplement the provisions given in Art. 210, so it’s important to check the application against Table 210.2. Note that Art. 210 doesn’t apply to circuits that supply only motor loads [210.1]. Although much of Art. 210 addresses residential applications, our focus here is on industrial and commercial applications.
Identification
The neutral conductor of a branch circuit must be identified per 200.6.
Insulated equipment grounding conductors up through size 6 AWG must have a continuous outer green finish (or green with one or more yellow stripes) [250.119]. On equipment grounding conductors 4 AWG and larger, insulation can be permanently reidentified with green marking at every point where the conductor is accessible [250.119(A)].
How do you correctly identify ungrounded conductors? If the branch circuits are supplied from:
• More than one nominal voltage system, apply 210.5(C)(1).
• DC power systems, apply 210.5(C)(2).
GFCI
You must install a ground fault circuit interrupter (GFCI) device at a readily accessible location [210.8] when you have 15A and 20A, 125V receptacles in any of the following locations:
1) Bathrooms, whether commercial or industrial.
2) For dwellings, receptacles installed to serve kitchen countertops [212.8(A)(6)]. In nondwelling-type kitchens, all 15A and 20A, 125V receptacles, regardless if they serve a countertop area [210.8(B)(2)]. An area such as an employee breakroom with a sink and cord- and plug-connected cooking appliance, such as a microwave oven, isn’t considered a kitchen (Fig. 2).
3) Rooftops, but they don’t have to be readily accessible other than from the rooftop. A 15A or 20A, 125V receptacle must be installed within 25 ft of heating, air-conditioning, and refrigeration equipment [210.63].
4) Outdoors, unless the receptacle is supplied by a branch circuit dedicated to fixed electric snow-melting, deicing, or pipeline and vessel heating equipment. The exclusion applies only if the receptacle isn’t readily accessible and the equipment or receptacle has ground fault protection of equipment (GFPE) [426.28 and 427.22].
5) Sink, if within 6 ft of its outside edge. In industrial laboratories, receptacles that supply equipment where removal of power would introduce a greater hazard don’t have to be GFCI protected. Receptacles in patient bed locations of general care or critical care areas of health care facilities don’t have to be GFCI protected, unless they are in a bathroom.
6) Indoor wet locations, though from a design standpoint you should avoid installing them there in the first place. If they are installed, it’s smart (but not NEC-required) to take additional practicable measures to keep water away (e.g., installing splash guards) or keep it from pooling near the receptacle (e.g., nonconductive grating with drain).
7) Locker rooms that have associated showering facilities. As with indoor wet locations, you can take non NEC-required measures to further improve safety.
8) Garages, service bays, and similar areas, but this excludes those in showrooms or exhibition halls.
Branch circuits required
How do you determine the minimum number of general lighting and general-use receptacle branch circuits? Divide the total calculated load (in amperes) by the ampere rating of the circuits used [210.11(A)].
If you calculate the load based on volt-amperes/square foot, you must provide the wiring system to serve the calculated load, and the loads must be evenly proportioned among multioutlet branch circuits within the panelboard [210.11(A)].
Conductor sizing
You must size branch circuit conductors the larger of [210.19(A)(1)]:
• 125% of the continuous loads, plus 100% of the noncontinuous loads (based on the terminal temperature rating ampacities as listed in Table 310.15(B)(16)).
• The maximum load to be served after the application of any adjustment or correction factors.
If the assembly (including the OCPD) is listed for operation at 100% of its rating, you can size the conductors at 100% of the continuous load, although these are very rare for branch circuits.
Branch circuits that supply more than one receptacle must have an ampacity of at least the rating of the circuit OCPD [210.23].
Overcurrent protection
Branch circuit OCPDs must have a rating of at least 125% of the (sum of the) continuous loads, plus 100% of the noncontinuous loads [210.20(A)], unless the assembly is rated for operation at 100% of its rating.
Outlet device rating
Lampholders connected to a branch circuit rated more than 20A must be of the heavy-duty type [210.21(A)]. Fluorescent lampholders aren’t rated heavy duty, so fluorescent luminaires can’t be installed on circuits rated more than 20A.
A single receptacle on an individual branch circuit must have an ampacity of at least the rating of the OCPD. A duplex receptacle is considered two receptacles.
If connected to a branch circuit that supplies two or more receptacles:
• The total cord- and plug-connected load can’t exceed 80% of the receptacle rating.
• Receptacles must conform to the values listed in Table 210.21(B)(3), based on the rating of the OCPD (Fig. 3).
Permissible loads
An individual branch circuit can supply any load that doesn’t exceed the ampere rating of the branch circuit [210.22].
Branch circuits rated 15A or 20A supplying two or more outlets must supply only loads per 210.23(A).
A 15A or 20A branch circuit can supply lighting and/or equipment. Except for temporary installations [590.4(D)], 15A or 20A circuits can supply both lighting and receptacles on the same circuit.
Cord- and plug-connected equipment not fastened in place (e.g., a table saw), must not have an ampere rating more than 80% of the branch circuit rating.
Equipment fastened in place (other than luminaires) must not be rated more than 50% of the branch circuit ampere rating if this circuit supplies luminaires and/or receptacles.
Multiwire branch circuits
A multiwire branch circuit (MWBC) consists of two or more ungrounded conductors with a common neutral conductor [Art. 100 Branch Circuit, Multiwire]. There must be a difference of potential (voltage) between the ungrounded conductors and an equal voltage from each ungrounded conductor to the common neutral (Fig. 4).
All conductors of an MWBC must originate from the same panelboard [210.4(A)]. Each MWBC must have a means to simultaneously disconnect all ungrounded conductors where the MWBC originates [210.4(B)]. You can use individual single-pole circuit breakers with handle ties identified for the purpose [240.15(B)(1)].
MWBC must supply only line-to-neutral loads [210.4(C)], except they can supply:
• An individual piece of line-to-line utilization equipment (e.g., range).
• Both line-to-line and line-to-neutral loads if the circuit’s protected by a device with a common internal trip that opens all ungrounded conductors of the MWBC simultaneously under a fault condition, such as a multipole circuit breaker (Fig. 5).
The ungrounded and neutral conductors must be grouped together by cable ties or similar means where the MWBC originates [210.4(D)]. This isn’t required if a single raceway contains the conductors, if they’re in a cable (unique to that circuit) that makes the grouping obvious, or if the conductors are tagged with circuit numbers (Fig. 6).
While the NEC permits using an MWBC, doing so may not always make sense from a design standpoint today. For example, today’s lighting circuits normally present nonlinear loads that discourage some people from sharing a neutral.
Working smarter
Article 210 is large and detailed. To be able to use it quickly (and avoid being overwhelmed), you can exclude large portions of it as we did in this discussion. If your application isn’t residential, you can skip over the subsections with residential requirements. You can apply this same strategy with other characteristics, such as voltage level.
If your work is always of the same type (e.g., industrial under 600V), consider using a highlighter to mark the sections that apply. Or you can use a simple color coding scheme to quickly guide your eye to the part of the job you’re now working on; for example, blue for conductors and yellow for receptacles.
Holt is the owner of Mike Holt Enterprises, Inc. in Leesburg, Fla. He can be reached at www.mikeholt.com.
