ICC user note:
About this chapter: Chapter 37 addresses the sizing of conductors for feeders and branch circuits, specifies the required branch circuits, provides for overcurrent protection of such conductors, specifies limitations for branch circuit loading, and addresses panel board ratings and protection. Design and installation processes move directly from the service to feeders and branch circuits.
Exception: The grounded conductors of feeders that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continuous and noncontinuous load. [215.1(A)(1) Exception No. 3]
Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used. [310.14(A)(2)]
Exception: Where different ampacities apply to portions of a circuit, the higher ampacity shall be permitted to be used where the total portion(s) of the circuit with the lower ampacity does not exceed the lesser of 10 feet (3048 mm) or 10 percent of the total circuit. [310.14(A)(2) Exception]
The ungrounded and grounded circuit conductors of each multiwire branch circuit shall be grouped by wire markers, cable ties or similar means in at least one location within the panelboard or other point of origination. [200.4(B), 210.4(D)]
Exception: Grouping shall not be required where the circuit conductors enter from a cable or raceway unique to the circuit, thereby making the grouping obvious, or where the conductors pass through a box or conduit body without a loop as described in Section E3905.12.2.1 or without a splice or termination. [200.4(B) Exceptions 1 and 2]
The voltage ratings of branch circuits that supply luminaires or receptacles for cord-and-plug-connected loads of up to 1,400 volt-amperes or of less than 1/4 horsepower (0.186 kW) shall be limited to a maximum rating of 120 volts, nominal, between conductors.
Branch circuits that supply cord-and-plug-connected or permanently connected utilization equipment and appliances rated at over 1,440 volt-amperes or 1/4 horsepower (0.186 kW) and greater shall be rated at 120 volts or 240 volts, nominal. [210.6(A), (B), and (C)]
A room air conditioner shall be considered as a single motor unit in determining its branch-circuit requirements where all the following conditions are met:
BRANCH-CIRCUIT REQUIREMENTS—SUMMARYa, b
TABLE E3702.14 (Table 210.24)
|15 amp||20 amp||30 amp|
Minimum size (AWG) circuit conductors
|Maximum overcurrent-protection device rating
|Receptacle rating (amperes)||
15 or 20
|Maximum load (amperes)||15||20||30|
A minimum of one 20-ampere branch circuit shall be provided to supply bathroom receptacle outlet(s) required by Section E3901.6 and any countertop or similar work surface receptacle outlets. Such circuits shall have no other outlets. [210.11(C)(3)]
Exception: Where the 20-ampere circuit supplies a single bathroom, outlets for other equipment within the same bathroom shall be permitted to be supplied in accordance with Section E3702. [210.11(C)(3) Exception]
In addition to the number of branch circuits required by other parts of this section, not less than one 120-volt, 20-ampere branch circuit shall be installed to supply receptacle outlets required by Section E3901.9 in attached garages and in detached garages with electric power. This circuit shall not have other outlets.
Exception: This circuit shall be permitted to supply readily accessible outdoor receptacle outlets.
|LOAD CALCULATION PROCEDURE||APPLIED DEMAND FACTOR|
|Lighting and receptacles: A unit load of not less than 3 VA per square foot of total floor area shall constitute the lighting and 120-volt, 15- and 20-ampere general use receptacle load. 1,500 VA shall be added for each 20-ampere branch circuit serving receptacles in the kitchen, dining room, pantry, breakfast area and laundry area.||100 percent of first 3,000 VA or less and 35 percent of that in excess of 3,000 VA.|
|Appliances and motors: The nameplate rating load of all fastened-in-place appliances 1/4 horsepower or greater, or 500 watts or greater, that are fastened in place, other than dryers, ranges, air-conditioning and space-heating equipment.||100 percent of load for three or less appliances. 75 percent of load for four or more appliances.|
|Fixed motors: Full-load current of motors plus 25 percent of the full load current of the largest motor.|
|Electric clothes dryer: The dryer load shall be 5,000 VA for each dryer circuit or the nameplate rating load of each dryer, whichever is greater.|
|Cooking appliances: The nameplate rating of ranges, wall-mounted ovens, counter-mounted cooking units and other cooking appliances rated in excess of 1.75 kVA shall be summed.||Demand factors shall be as allowed by Table E3704.2(2).|
|Plus the largest of either the heating or cooling load|
|Largest of the following two selections:
For SI: 1 square foot = 0.0929 m2.
DEMAND LOADS FOR ELECTRIC RANGES, WALL-MOUNTED OVENS, COUNTER-MOUNTED COOKING UNITS AND OTHER COOKING APPLIANCES OVER 13/4 kVA RATINGa, b
TABLE E3704.2(2) (220.55 and Table 220.55)
|NUMBER OF APPLIANCES||MAXIMUM DEMANDb, c||DEMAND FACTORS (percent)d|
|Column A maximum 12 kVA rating||Column B less than 31/2 kVA rating||Column C 31/2 to 83/4 kVA rating|
|CONDUCTOR SIZE||CONDUCTOR TEMPERATURE RATING||CONDUCTOR SIZE|
|AWG kcmil||Types TW, UF||Types RHW, THHW, THW, THWN, USE, XHHW||Types RHW-2, THHN, THHW, THW-2, THWN-2, XHHW, XHHW-2, USE-2||Types TW, UF||Types RHW, THHW, THW, THWN, USE, XHHW||Types RHW-2, THHN, THHW, THW-2, THWN-2, XHHW, XHHW-2, USE-2||AWG kcmil|
|Copper||Aluminum or copper-clad aluminum|
For SI: °C = [(°F) — 32]/1.8.
TABLE E3705.2 [310.15(B)(1)]AMBIENT TEMPERATURE CORRECTION FACTORS
|For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below.|
|Ambient Temperature (°C)||Temperature Rating of Conductor||Ambient Temperature (°F)|
10 or less
|1.29||1.20||1.15||50 or less|
For SI: °C = [(°F) — 32]/1.8.
Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled for distances greater than 24 inches (610 mm) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table E3705.3. [310.15(C)(1)]
Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for:
All ungrounded branch-circuit and feeder conductors shall be protected against overcurrent by an overcurrent device installed at the point where the conductors receive their supply. Overcurrent devices shall not be connected in series with a grounded conductor. Overcurrent protection and allowable loads for branch circuits and for feeders that do not supply the entire load associated with a one-family dwelling or the entire load associated with an individual dwelling unit in a two-family dwelling shall be in accordance with this chapter.
Branch-circuit conductors and equipment shall be protected by overcurrent protective devices having a rating or setting not exceeding the allowable ampacity specified in Table E3705.1 and Sections E3705.2, E3705.3 and E3705.4 except where otherwise permitted or required in Sections E3705.5.1 through E3705.5.3. [240.4, 240.21, and 310.12(B)]
The next higher standard overcurrent device rating, above the ampacity of the conductors being protected, shall be permitted to be used, provided that all of the following conditions are met:
TABLE E3705.5.3 [240.4(D)]OVERCURRENT-PROTECTION RATING
|COPPER||ALUMINUM OR COPPER-CLAD ALUMINUM|
|Size (AWG)||Maximum overcurrent-protection-device ratinga (amps)||Size (AWG)||Maximum overcurrent-protection-device ratinga (amps)|
TABLE E3705.6 (Table 240.6)STANDARD APMPERE RATING
FOR FUSES AND INVERSE TIME CIRCUIT BREAKERS
|Standard Ampere Ratings|
Circuit breakers and switches containing fuses shall: