Menu
Search
8 NEC Basic Feeder Circuit Sizing Requirements
8 NEC Basic Feeder Circuit Sizing Requirements (photo credit: acs-mtv.com)

Feeder circuit loads

Once the branch circuit loads are calculated, the feeder circuit loads may be calculated by applying demand factors to the branch circuit loads.

  1. General Lighting Loads (Article 220.42)
  2. Show window or track lighting (Article 220.43)
  3. Receptacles in other than dwelling units (Article 220.44)
  4. Motors (Article 220.50)
  5. Fixed Electric Space Heating (Article 220.51)
  6. Noncoincident Loads (Article 220.60)
  7. Feeder neutral load (Article 220.61)
  8. Continuous Loads (Article 215.3)

1. General Lighting Loads

(Article 220.42)

The feeder general lighting load can be calculated by multiplying the branch circuit general lighting load calculated per B.) 1.), for those branch circuits supplied by the feeder, by a demand factor per table 1 (NEC table 220.42).

Table 1 – Lighting load feeder demand factors (NEC [3] table 220.42)

Type of OccupancyPortion of Lighting Load to Which Demand Factor Applies
(Volt-Amperes)
Demand Factor
(Percent)
Dwelling units First 3,000 or less at100
 From 3,001 to 120,000 at35
 Remainder over 120,000 at25
Hospitals* First 50,000 or less at40
 Remainder over 50,000 at20
Hotels and motels, including apartment houses without provision for cooking by tenants* First 20,000 or less at50
 From 20,001 to 100,000 at40
 Remainder over 100,000 at30
Warehouses (storage) First 12,500 or less at100
 Remainder over 12,500 at50
All others Total volt-amperes100

* The demand factors of this table shall not apply to the calculated load of feeders or services supplying areas in hospitals, hotels, and motels where the entire lighting is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms.

Go back to Index ↑


2. Show window or track lighting

(Article 220.43)

Show windows must use a calculated value of 660 voltamperes per linear meter (200 volt-amperes per linear foot), measured horizontally along its base. Track lighting in other than dwelling units must be calculated at an 150 volt-amperes per 660mm (2 ft.) of lighting track or fraction thereof.

Go back to Index ↑


3. Receptacles in other than dwelling units

(Article 220.44)

Demand factors for non-dwelling receptacle loads are given in table 2 (NEC table 220.44).

Portion of Receptacle Load to Which Demand Factor Applies
(Volt-Amperes)
Demand Factor (Percent)
 First 10 kVA or less at100
 Remainder over 10 kVA50

Go back to Index ↑


4. Motors (Article 220.50)

The feeder demands for these are calculated as follows:

The load calculation for several motors, or a motor(s) and other loads, is 125% of the full load current rating of the highest rated motor per II.) B.) ii.) above plus the sum of the full-load current ratings of all the other motors in the group, plus the ampacity required for the other loads (Article 430.24).

The load calculation for factory-wired multimotor and combination-load equipment should be based upon the minimum circuit ampacity marked on the equipment (Article 430.25) instead of the motor horsepower rating.

Where allowed by the Authority Having Jurisdiction, feeder demand factors may be applied based upon the duty cycles of the motors. No demand factors are given in the NEC for this situation.

Go back to Index ↑


5. Fixed Electric Space Heating

(Article 220.51)

The feeder loads for these must be calculated at 100% of the connected load.

Go back to Index ↑


6. Non-coincident loads

(Article 220.60)

Where it is unlikely that two or more noncoincident loads will be in use simultaneously, it is permissible to use only the largest loads that will be used at one time to be used in calculating the feeder demand.

Go back to Index ↑


7. Feeder neutral load

(Article 220.61)

The feeder neutral load is defined as the maximum load imbalance on the feeder. The maximum load imbalance for three-phase four-wire systems is the maximum net calculated load between the neutral and any one ungrounded conductor. A demand factor of 70% may be applied to this calculated load imbalance.

Refer to NEC article 220.61 for neutral reductions in systems other than three-phase, four-wire systems. This demand factor does not apply to non-linear loads; in fact, it may be necessary to oversize the neutral due to current flow from non-linear load triplen harmonics.

Go back to Index ↑


8. Continuous Loads

(Article 215.3)

The rating of the overcurrent protection for a feeder circuit must be at least the sum of the non-continuous load +125% of the continuous load, unless the overcurrent device is 100%-rated. Because the rating of the overcurrent protection determines the rating of the branch circuit (Article 210.3), the branch circuit must be sized for the non-continuous load +125% of the continuous load.

In the final feeder circuit load calculation, the continuous portion of the load should therefore be multiplied by 1.25 unless the overcurrent device for the circuit is 100%-rated. Note that motor loads are not included in this calculation as the 125% factor is already included in the applicable sizing per above.

Additional calculation data is given in NEC Article 220 for dwelling units, restaurants, schools, and farms.

As this article only presents the basic NEC requirements for load calculations, it is imperative to refer to the NEC itself when in doubt about a specific load sizing application. Computer programs are commercially available to automate the calculation of feeder and branch circuit loads per the NEC methodology described above.

Go back to Index ↑


References:
  • Load Planning – Bill Brown, P.E., Square D Engineering Services
  • IEEE Recommended Practice for Electric Power Distribution for Industrial Plants,
  • IEEE Standard 141-1993, December 1993.
  • Turan Gonen, Electric Power Distribution System Design, New York: McGraw-Hill, 1986, pp. 37-51
  • The National Electrical Code, NFPA 70, The National Fire Protection Association, Inc., 2005 Edition
  • IEEE Recommended Practice for Electric Power Systems in Commercial Buildings,
  • IEEE Standard 241-1990, December 1990.

About Author //

author-pic

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

9 Comments


  1. ahmed rahman
    May 16, 2015

    need power receptacles distribution in nondwelling buildings…..?


  2. ahmed rahman
    May 16, 2015

    pls .I need to know the recommended distribution of power receptacles in building rather than the dwelling buildings-I mean the commertial ,Industrial…etc


  3. Chang Hon Keong
    Jan 29, 2015

    Generally very informative and enables a clearer understanding of the fundamental behind the various available technical topics.


  4. jitendra darji
    Dec 23, 2014

    nice


  5. jitendra darji
    Dec 23, 2014

    very help full for me


  6. Charles Ooko
    Dec 22, 2014

    It is interesting to share technical experiences n knowledge in our humble profession.


  7. Abdullah Habib Zia
    Dec 20, 2014

    Awesome.


  8. Dadd Gabby
    Dec 17, 2014

    Hi Edvard Csanyi,
    Ever since i subscribed on your EEP newsletter, i always enjoy your news.
    I am a rapper and i have passion for electricity, please can you upload my music on one of your post.


  9. mina
    Dec 17, 2014

    Nice article

Leave a Comment

Tell us what you're thinking... we care about your opinion!


Get PDF