What Is The Minimum Branch-circuit Wire Size That May Be Installed In A Dwelling

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Usher ampacity Table 310.15(B)(sixteen) and Table 310.15(B)(3)(a) for adjusting the ampacity of a usher when there are more 3 current carrying conductors (CCC).

Code Change Summary: New code linguistic communication was added to clarify how to properly size branch circuit conductors.

The code language added to this section in the 2014 NEC is non a new concept. Information technology is just a clarification. Co-operative circuit conductors are still calculated the aforementioned way every bit before but the revised code linguistic communication is a bit more user friendly.

At present, it is clear than when sizing a branch circuit conductor, the larger of two values is used for the last selection of the conductor:

• Either 125% of the continuous load without any boosted adjustment or correction factors,

OR

• 100% of the load (not 125% of it) after applying adjustment and correction factors.

Before this lawmaking change, some electrician were taking 125% of the continuous load and then applying additional adjustment or correction factors which results in an oversized conductor. See the case below for the proper iii-step method to size the co-operative circuit:

Example: What minimum size copper type THW conductors are required to supply a 60 amp continuous load where there are 10 current conveying conductors (CCC) in the raceway?(For simplicity, assume all terminals are rated 75°C)

Stride 1, have sixty amps X 125% which = 75 amps. Select a THW copper conductor from Table 310.xv(B)(xvi) that tin carry 75 amps from the 75° column (#four AWG).

Pace two, take threescore amps ÷ fifty% (based on 10 CCC in the raceway and Table 310.15(B)(3)(a)).

threescore ÷ .50 = 120 amps. Select a THW copper conductor from Table 310.15(B)(16) that tin can deport 120 amps from the 75° column (#1 AWG).

Step iii, compare results from the starting time two steps and pick the larger wire which is 1 AWG copper.

Below is a preview of the NEC.  See the actual NEC text at NFPA.ORG for the complete code section. Once in that location, click on the "free access" tab and select the applicative yr of NFPA seventy (National Electrical code).

2011 Code Language:

210.19(A)(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-excursion conductor size, before the application of whatsoever adjustment or correction factors, shall take an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

2014 Code Language:

210.19(A)(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of 210.19(A)(1)(a) or (b).

(a) Where a branch circuit supplies continuous loads or whatever combination of continuous and noncontinuous loads, the minimum branch-circuit usher size shall take an allowable ampacity non less than the noncontinuous load plus 125 percentage of the continuous load.

(b) The minimum branch-excursion conductor size shall take an allowable ampacity not less than the maximum load to exist served afterwards the application of whatever adjustment or correction factors.

What Is The Minimum Branch-circuit Wire Size That May Be Installed In A Dwelling,

Source: https://www.electricallicenserenewal.com/Electrical-Continuing-Education-Courses/NEC-Content.php?sectionID=26.0

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