Section E3705 Conductor Sizing and Overcurrent Protection
|CONDUCTOR TEMPERATURE RATING||CONDUCTOR |
|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.
|Ambient Temperature |
|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.
- Adjustment factors shall not apply to conductors in raceways 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)]
- Adjustment factors shall not apply to type AC cable or to type MC cable without an overall outer jacket meeting all of the following conditions:
- Each cable has not more than three current-carrying conductors.
- The conductors are 12 AWG copper.
- Not more than 20 current-carrying conductors are bundled, stacked or supported on bridle rings. [310.15(B)(3)(4)]
- An adjustment factor of 60 percent shall be applied to Type AC cable and Type MC cable where all of the following conditions apply:
- The cables do not have an overall outer jacket.
- The number of current-carrying conductors exceeds 20.
- The cables are stacked or bundled longer than 24 inches (607 mm) without spacing being maintained. [310.15(B)(3)(4) Exception]
| NUMBER OF CURRENT-CARRYING
CONDUCTORS IN CABLE OR RACEWAY
| PERCENT OF VALUES IN
|41 and above||35|
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 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 310.15(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 |
|Maximum overcurrent- |
|Maximum overcurrent |
Circuit breakers and switches containing fuses 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)]