Chapter 12 Branch Circuits and Feeders Objectives Identify

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 branchcircuit conductors. Goodheart-Willcox Publisher Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Definitions • Service conductors – 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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Definitions • Panelboard – Single or multiple panels containing switches, fuses, and circuit breakers • Branch circuits – Transfer power to load devices Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Definitions Goodheart-Willcox Publisher Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Branch Circuits Goodheart-Willcox Publisher Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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% Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Lighting Loads • General 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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

General Lighting Loads Goodheart-Willcox Publisher Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Lighting Loads • Track 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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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. Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Demand Factors • Lighting load may be derated for feeder, panel, or service computations Goodheart-Willcox Publisher Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 airconditioning equipment Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Heating and Cooling Loads • Heating load computed at 100% of nameplate rating – Disconnect and overcurrent protection required – General rules for sizing overcurrent protection devices Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Commercial Service Load Computation Procedure 1. Determine general lighting load 2. If continuous load, increase load by 125% 3. Feeder and service loads, apply lighting demand factor 4. Compute air-conditioning and heating loads 5. Compute receptacle outlets 6. Demand factors for receptacle and kitchen equipment loads Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

Summary of Commercial Service Load Computation Procedure 7. Add sign lighting load 8. Compute motor loads 9. Increase largest motor load by 25% 10. Size service and service conductors 11. Size grounded service conductor 12. Derate neutral load by 70%, if over 200 amperes Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.