Branch-circuit and feeder conductors shall have ampacities not less than the maximum load to be served. Where a branch circuit or a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit or feeder conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the noncontinuous load plus 125 percent of the continuous load. [210.19(A)(1)(a) and 215.2(A)(1)(a)]
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. 2]
Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used. [310.15(A)(2)]
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 10 feet (3048 mm) or 10 percent of the circuit length figured at the higher ampacity, whichever is less. [310.15(A)(2) Exception]
The ungrounded and grounded circuit conductors of each multiwire branch circuit shall be grouped by cable ties or similar means in at least one location within the panelboard or other point of origination. [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 are identified at their terminations with numbered wire markers corresponding to their appropriate circuit number. [210.4(D) Exception].
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:
- It is cord- and attachment plug-connected.
- The rating is not more than 40 amperes and 250 volts; single phase.
- Total rated-load current is shown on the room air-conditioner nameplate rather than individual motor currents.
- The rating of the branch-circuit short-circuit and ground-fault protective device does not exceed the ampacity of the branch-circuit conductors, or the rating of the branch-circuit conductors, or the rating of the receptacle, whichever is less. [440.62(A)]
The requirements for circuits having two or more outlets, or receptacles, other than the receptacle circuits of Sections E3703.2, E3703.3 and E3703.4, are summarized in Table E3702.14. Branch circuits in dwelling units shall supply only loads within that dwelling unit or loads associated only with that dwelling unit. Branch circuits installed for the purpose of lighting, central alarm, signal, communications or other purposes for public or common areas of a two-family dwelling shall not be supplied from equipment that supplies an individual dwelling unit. (210.24 and 210.25)
TABLE E3702.14 (Table 210.24)
BRANCH-CIRCUIT REQUIREMENTS-SUMMARYa, b
|15 amp||20 amp||30 amp|
Minimum size (AWG)circuit conductors
|Maximum overcurrent- |
protection device rating
|Outlet devices: |
Lampholders permittedReceptacle rating (amperes)
|Any type 15 |
|Any type |
15 or 20
|Maximum load (amperes)||15||20||30|
- These gages are for copper conductors.
- N/A means not allowed.
A minimum of two 20-ampere-rated branch circuits shall be provided to serve all wall and floor receptacle outlets located in the kitchen, pantry, breakfast area, dining area or similar area of a dwelling. The kitchen countertop receptacles shall be served by a minimum of two 20-ampere-rated branch circuits, either or both of which shall also be permitted to supply other receptacle outlets in the same kitchen, pantry, breakfast and dining area including receptacle outlets for refrigeration appliances. [210.11(C)(1) and 210.52(B)(1) and (B)(2)]
A minimum of one 20-ampere branch circuit shall be provided to supply bathroom receptacle outlet(s). 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)
The minimum load in volt-amperes shall be calculated in accordance with the load calculation procedure prescribed in Table E3704.2(1). The associated table demand factors shall be applied to the actual load to determine the minimum load for feeders. (220.40)
TABLE E3704.2(1) (Table 220.12, 220.14, Table 220.42, 220.50, 220.51, 220.52, 220.53, 220.54, 220.55, and 220.60)
FEEDER LOAD CALCULATION
|LOAD CALCULATION PROCEDURE||APPLIED DEMAND FACTOR|
|Lighting and receptacles: A unit load of not |
less than 3 VA per square footof total floor area shall constitute the lighting and 120-volt, 15- a
nd 20-ampere general use receptacle load. 1,500 VA shall be addedfor 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 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.
TABLE E3704.2(2) (220.55 and Table 220.55)
DEMAND LOADS FOR ELECTRIC RANGES, WALL-MOUNTED OVENS, COUNTER-MOUNTED COOKING UNITS AND OTHER COOKING APPLIANCES OVER 13/4 kVA RATINGa, b
|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
- Column A shall be used in all cases except as provided for in Footnote d.
- For ranges all having the same rating and individually rated more than 12 kVA but not more than 27 kVA, the maximum demand in Column A shall be increased 5 percent for each additional kVA of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kVA.
- For ranges of unequal ratings and individually rated more than 8.75 kVA, but none exceeding 27 kVA, an average value of rating shall be computed by adding together the ratings of all ranges to obtain the total connected load (using 12 kVA for any ranges rated less than 12 kVA) and dividing by the total number of ranges; and then the maximum demand in Column A shall be increased 5 percent for each kVA or major fraction thereof by which this average value exceeds 12 kVA.
- Over 1.75 kVA through 8.75 kVA. As an alternative to the method provided in Column A, the nameplate ratings of all ranges rated more than 1.75 kVA but not more than 8.75 kVA shall be added and the sum shall be multiplied by the demand factor specified in Column B or C for the given number of appliances.
|CONDUCTOR TEMPERATURE RATING||CONDUCTOR |
RHW, THHW,THW, THWN,
RHW-2, THHN,THHW, THW-2,
THWN-2, XHHW,XHHW-2, USE-2
RHW, THHW,THW, THWN,
RHW-2, THHN, THHW, THW-2,
THWN-2, XHHW,XHHW-2, USE-2
|Copper||Aluminum or copper-clad aluminum|
For SI: °C = [(°F) - 32]/1.8.
- See Table E3705.5.3 for conductor overcurrent protection limitations.
TABLE E3705.2 [Table 310.15(B)(2)(a)]
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.
|Temperature Rating of Conductor||Ambient Temperature|
|10 or less||1.29||1.20||1.15||50 or less|
For SI: 1 °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(B)(3)]
- Adjustment factors shall not apply to conductors in nipples having a length not exceeding 24 inches (610 mm). [310.15(B)(3)(2)]
- Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit having a length not exceeding 10 feet (3048 mm) and the number of conductors does not exceed four. [310.15(B)(3)(3)]
- 3.1. Each cable has not more than three current-carrying conductors.
- 3.2. The conductors are 12 AWG copper.
- 3.3. Not more than 20 current-carrying conductors are bundled, stacked or supported on bridle rings. [310.15(B)(3)(4)]
- 4.1. The cables do not have an overall outer jacket.
- 4.2. The number of current-carrying conductors exceeds 20.
- 4.3. The cables are stacked or bundled longer than 24 inches (607 mm) without spacing being maintained. [310.15(B)(3)(5)]
Except where the equipment is marked otherwise, termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
- Conductors rated 60°C (140°F);
- Conductors with higher temperature ratings, provided that the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used;
- Conductors with higher temperature ratings where the equipment is listed and identified for use with such conductors; or
- For motors marked with design letters B, C, or D conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used provided that the ampacity of such conductors does not exceed the 75°C (167°F) ampacity. [110.14(C)(1)(a)]
Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for:
- Conductors rated 75°C (167°F).
- Conductors with higher temperature ratings provided that the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or provided that the equipment is listed and identified for use with such conductors. [110.14(C)(1)(b)]
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 serve as the main power feeder to the dwelling unit load 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 310.15(B)(7)(2)]
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:
- The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord- and plug-connected portable loads.
- The ampacity of conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
- The next higher standard device rating does not exceed 400 amperes. [240.4(B)]
Except as specifically permitted by Section E3705.5.4, the rating of overcurrent protection devices shall not exceed the ratings shown in Table E3705.5.3 for the conductors specified therein. [240.4(D)]
TABLE E3705.5.3 [240.4(D)]
|COPPER||ALUMINUM OR COPPER-CLAD |
Overcurrent devices shall:
- Be readily accessible. [240.24(A)]
- Not be located where they will be exposed to physical damage. [240.24(C)]
- Not be located where they will be in the vicinity of easily ignitible material such as in clothes closets. [240.24(D)]
- Not be located in bathrooms. [240.24(E)]
- Not be located over steps of a stairway.
- Be installed so that the center of the grip of the operating handle of the switch or circuit breaker, when in its highest position, is not more than 6 feet 7 inches (2007 mm) above the floor or working platform. [240.24(A)]