Chapter 12 Branch Circuits and Feeders

Objectives Identify the feeder and branch circuit portions of a distribution system. Describe the various types of branch circuits. Define the functions of a feeder and the functions of branch-circuit conductors. Goodheart-Willcox Publisher

Objectives Calculate lighting and receptacle loads using Code requirements. Size branch circuits in accordance with the Code. Determine branch circuit overcurrent protection required by the Code. Use the Code to size feeder conductors. Goodheart-Willcox Publisher

Definitions Service conductors Feeder Subfeeders From power company terminals to main service disconnect Feeder From main distribution or disconnect to another distribution/load center or panelboard Subfeeders To panelboards, load centers, and disconnect switches that supply branch circuits

Definitions Panelboard Branch circuits Single or multiple panels containing switches, fuses, and circuit breakers Branch circuits Transfer power to load devices

Definitions Goodheart-Willcox Publisher

Branch Circuits Extend past final overcurrent protective device Classifications Individual, multioutlet, general purpose, appliance, multiwire Sized for load it will supply Depends on rating of overcurrent device

Branch Circuits Goodheart-Willcox Publisher

Branch-Circuit Voltage Limitations based on equipment being supplied Residences and hotel rooms circuits Circuits 120 volts and less Branch circuits between 120 and 277 volts Circuits between 277 and 600 volts

Branch Circuits Amperage rating greater than maximum load Ampacity in multiple-load circuits corresponds to rating of overcurrent protective device Multiwire branch circuits Grounded conductor and two or more ungrounded conductors Individual or multioutlet circuit

Conductor Color Code Grounded conductor 6 AWG or less White or with color stripe, gray, or white stripes Wires from different systems in same raceway Neutrals distinguished by different color Equipment grounding conductor Green or with yellow stripes, or bare Hot conductors are black, blue, or red

Continuous Loads Longer than three hours Must not exceed 80% of circuit rating allotted 80% rule not used with overcurrent protective device for continuous operation at 100%

Lighting Loads General lighting load Show-window lighting load Determined by load per area method or full-load current of fixtures used Show-window lighting load Not part of general lighting load 200 volt-amperes per linear foot or max volt-ampere rating of equipment

General Lighting Loads Goodheart-Willcox Publisher

Code Alert Shadow Window Article 100 Any window displaying goods or advertising Light in Show Windows Section 410.14 Chain-supported fixtures may be externally wired No other externally wired fixtures

Lighting Loads Track lighting Sign and outline lighting Minimum load is 150 volt-amperes for 2′ of track Sign and outline lighting At least one circuit dedicated Minimum load of 1200 volt-amperes Additional loads computed separately

Code Alert Lighting Track Section 410.2 Manufactured assembly designed to support and energize luminaries that can be repositioned on track. Can alter length by addition or subtraction of track sections.

Demand Factors Lighting load may be derated for feeder, panel, or service computations Goodheart-Willcox Publisher

Receptacle Loads Most do not supply continuous loads Receptacle ampere rating based on circuit type Individual or multiple Number of receptacles on branch circuit Multiply circuit voltage and amperage Divide by 180 volt-amperes

Equipment Loads Most are noncontinuous Required load supplied identical to equipment requirement Hard-wired or cord-and-plug connected Ampacity of conductors equal to or exceed that of appliance 125% of motor current rating

Code Alert Kitchen Demand Factors Section 220.56 Demand factors applied to thermostatic control or intermittent use as kitchen equipment. Not applied to space-heating, ventilating, or air-conditioning equipment

Heating and Cooling Loads Heating load computed at 100% of nameplate rating Disconnect and overcurrent protection required General rules for sizing overcurrent protection devices

Heating and Cooling Loads Air-conditioning load determined from nameplate data Larger branch-circuit current rating or full-load current rating for sizing 125% of the largest motor for two or more motors 115% of the full-load current for single motor

Feeders Conductors between service equipment and branch-circuit overcurrent devices Loading dependent on total power requirement of system Factors for correct feeder size, type, and overcurrent protection

Commercial Service Load Computation Procedure Determine general lighting load If continuous load, increase load by 125% Feeder and service loads, apply lighting demand factor Compute air-conditioning and heating loads Compute receptacle outlets Demand factors for receptacle and kitchen equipment loads

Summary of Commercial Service Load Computation Procedure Add sign lighting load Compute motor loads Increase largest motor load by 25% Size service and service conductors Size grounded service conductor Derate neutral load by 70%, if over 200 amperes