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Feeder and Service Load Calculations

Thursday, March 13th, 2014

Design Master Electrical can calculate feeder and service loads based upon NEC 220 Part III and Part IV. This article lists each code reference and how to properly set up your model for that calculation. This article is intended to be used as a reference together with the NEC and is based on the assumption that you know which section in the NEC you need to comply with. You can then look up the appropriate section below and see how to model it.

References will be made to load calculation methods throughout this article. To set the load calculation method for a panel, in the Panel dialog box, press the Feeder and Service Calculation Settings button.

References will be made to fixed loads and load types throughout this article. To assign fixed loads to a circuit, in the Circuiting dialog box, press the Set Circuit Information button.

Part III. Feeder and Service Load Calculations

220.42 General Lighting. To use the demand factors for general lighting in Table 220.42, you must also use the general lighting calculations. Otherwise, all lighting has a calculated load of 125%. In the Feeder and Service Calculation Settings dialog box, use the Occupancy Areas section to set the occupancy areas associated with the panel. Set the areas on the panels furthest from the utility. The areas will be carried up to the upstream panels. The area on a panel is the sum of the areas specified in the Occupancy Areas section for that panel and all of the areas of the panels connected to it.

Dwelling units: Set the Type of Occupancy to Dwelling Unit. Use the Area field to set the area. Set the Demand Factor to Dwelling Unit.

Hotels and motels: Set the Type of Occupancy to Hotel or Motel. Use the Area field to set the area. Set the Demand Factor to Hotel or Motel.

Warehouses: Set the Type of Occupancy to Warehouse. Use the Area field to set the area. Set the Demand Factor to Warehouse.

All others: Set the Type of Occupancy to the most appropriate type based upon NEC Table 220.12. If none of the types is applicable, select Custom and use the Description and Unit Load fields to define the occupancy type. Use the Area field to set the area. Set the Demand Factor to Other (Continuous) or Other (Noncontinuous).

220.43 Show-Window and Track Lighting. Either create a fixture to represent the load or use fixed loads.

Create a Fixture: Create a fixture in the Light Fixture Project Schedule to represent the load. For show windows, each fixture will represent 1 linear foot of show window. Set the Load to 0.2 kVA. For track lighting, each fixture will represent 2 feet of track. Set the Load to 0.15 kVA. Insert fixtures on the drawing to represent the appropriate length of show window or track. Circuit the fixtures normally.

Fixed Loads:  Use the General: Lighting load type for show-window or track lighting. Draft the lighting by either inserting light fixtures that are not circuited or have 0 load, or using standard CAD drafting commands to insert light fixtures that are not connected to the Design Master Electrical database.

220.44 Receptacle Loads — Other Than Dwelling Units. Use the General: Receptacles load type for receptacles that should be calculated based upon this section. Typically, the load for each receptacle will be 0.18 kVA. The load on the panel will be based upon NEC Table 220.44.

220.50 Motors. See the Motor Load Calculations article for a description of how to use the Single Motor and Multiple Motor fields to specify motors.

220.51 Fixed Electrical Space Heating. Use the General: Heating load type for devices that should be calculated based upon this section.

220.52 Small-Appliance and Laundry Loads — Dwelling Unit. Set the Load Calculation Method to General Commercial or Dwelling Unit, Section III to use this code section.

(A) Small-Appliance Circuit Load. Use the Dwelling Unit: Small Appliance load type for devices that are on a small appliance circuit. The specific load on the device does not matter. If any devices with this load type are on a circuit, the load on the circuit will be 1.5 kVA.

(B) Laundry Circuit Load. Use the Dwelling Unit: Laundry load type for devices on a laundry circuit. The load on the circuit will be at least 1.5 kVA. If the load on the devices is greater than 1.5 kVA, the actual device load is used.

220.53 Appliance Load — Dwelling Unit(s). Set the Load Calculation Method to General Commercial or Dwelling Unit, Section III to use this code section.

Use the Dwelling Unit: Appliance, Continuous or Dwelling Unit: Appliance, Noncontinuous load type for devices that are appliances. If the appliance is also a motor, use the Dwelling Unit: Appliance Motor load type. Use the Multiplier field to specify the number of appliances the load represents.

220.54 Electrical Clothes Dryers — Dwelling Unit(s). Set the Load Calculation Method to General Commercial or Dwelling Unit, Section III to use this code section.

Use the Dwelling Unit: Electric Dryer load type for electric dryers. You must specify a value of at least 5 kVA for the load on the dryer. Use the Multiplier field to specify the number of appliances the load represents.

220.55 Electrical Cooking Appliances in Dwelling Units and Household Cooking Appliances Used in Instructional Programs. Use the Dwelling Unit: Electric Cooking load type for electric ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances. Use the Multiplier field to specify the number of appliances the load represents.

220.56 Kitchen Equipment — Other Than Dwelling Unit(s). Use the General: Kitchen load type for commercial kitchen equipment. Use the Multiplier field to specify the number of appliances the load represents.

220.60 Noncoincident Loads. When both noncoincident loads are connected to the same panel, use the General: Diverse load type for the smaller of the two loads. Set the Multiplier field to 0. For heating and cooling loads, use the General: Heating, General: Cooling, Largest Motor, General: Cooling, Other Motors, and General: Heating and Cooling Motor load types. The larger of the heating or cooling load will be used for the feeder load total. There is no way to model noncoincident loads connected to separate panels. If you specify the load normally, panels that have both loads on them will have feeder load totals that are too high. If you specify the load using the Diverse load type, the panel with the diversified device on it will have a feeder load total that is too low.

Part IV. Option Feeder and Service Load Calculations

220.82 Dwelling Unit. Set the Load Calculation Method to Dwelling Unit to calculate the feeder load total using this section.

(A) Feeder and Service Load. You are responsible for specifying a 100A feeder.

(B) General Loads.

(1) Set the Type of Occupancy to Dwelling Unit. Use the Area field to set the area. Set the Demand Factor to Dwelling Unit.

(2) Use the Dwelling Unit: Small Appliance and Dwelling Unit: Laundry load types for devices on these circuits.

(3) Use the Dwelling Unit: Appliance load type for a, c, and d. Use the Dwelling Unit: Electric Cooking load type for b.

(4) Use the Dwelling Unit: Appliance Motor load type for these motors.

(C) Heating and Air-Conditioning Load.

(1) Use the Dwelling Unit: Cooling, Largest Motor, Dwelling Unit: Cooling, Other Motors, and Dwelling Unit: Heating and Cooling Motor load types for this load.

(2) Use the Dwelling Unit: Heating and Cooling Motor load type for the heat pump load.

(3) Use the Dwelling Unit: Heating and Cooling Motor load type for the heat pump compressor. Use the Dwelling Unit: Heating load type for supplemental heating.

(4) Use the Dwelling Unit: Heating load type for the electric space heaters. Use the Multiplier field to specify the number of heaters the load represents.

(5) Use the Dwelling Unit: Heating load type for the electric space heaters. Use the Multiplier field to specify the number of heaters the load represents.

(6) Use the General: Heating load type for continuous heating. Do not use any of the Dwelling Unit heating or cooling load types if you need to use this code section.

220.83 Existing Dwelling Unit. Set the Load Calculation Method to Existing Dwelling Unit to calculate the feeder load total using this section.

(A) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is Not to Be Installed.

(1) Set the Type of Occupancy to Dwelling Unit. Use the Area field to set the area. Set the Demand Factor to Dwelling Unit.

(2) Use the Dwelling Unit: Small Appliance and Dwelling Unit: Laundry load types for devices on these circuits.

(3) Use the Dwelling Unit: Appliance load type for a, c, and d. Use the Dwelling Unit: Electric Cooking load type for b.

(B) Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is to Be Installed. Use the Dwelling Unit: Cooling, Largest Motor and Dwelling Unit: Cooling, Single Motor load types for air-conditioning equipment. Use the Dwelling Unit: Heating load type for central electric space heating and separately controlled space-heating units.

(1) Set the Type of Occupancy to Dwelling Unit. Use the Area field to set the area. Set the Demand Factor to Dwelling Unit.

(2) Use the Dwelling Unit: Small Appliance and Dwelling Unit: Laundry load types for devices on these circuits.

(3) Use the Dwelling Unit: Appliance load type for a, c, and d. Use the Dwelling Unit: Electric Cooking load type for b.

220.84 Multifamily Dwelling. Set the Load Calculation Method to Multifamily Dwelling to calculate the feeder load total using this section.

(A) Feeder or Service Load. This calculation method is for three or more dwelling units. You must use a different calculation method for a single dwelling unit. The Load Calculation Method selection includes a choice for the calculation that will be used for a single dwelling unit. This calculation method also requires 8 kVA of electric cooking load if there is no electric cooking, which must be manually specified on the panel.

(B) House Loads. Enter house loads as you would for NEC 220 Part III.

(C) Connected Loads.

(1) Set the Type of Occupancy to Dwelling Unit. Use the Area field to set the area. Set the Demand Factor to Dwelling Unit.

(2) Use the Dwelling Unit: Small Appliance and Dwelling Unit: Laundry load types for devices on these circuits.

(3) Use the Dwelling Unit: Appliance load type for a, c, and d. Use the Dwelling Unit: Electric Cooking load type for b.

(4) Use the Dwelling Unit: Appliance Motor load type for these motors.

(5) Use the Dwelling Unit: Heating, Dwelling Unit: Cooling, Largest Motor, Dwelling Unit: Other Motors, and Dwelling Unit: Heating and Cooling Motor load types for the air-conditioning and electric space-heating loads.

220.85 Two Dwelling Units. If two dwelling units are calculated using the Multifamily Dwelling load calculation method, it is assumed that they are identical. The total load for both dwelling units is multiplied by 1.5 to increase it from 2 to 3 units, then a demand factor of 45% is applied.

220.86 Schools. Set the Load Calculation Method to School to use this code section.

220.87 Determining Existing Loads. In the Feeder and Service Calculation Settings dialog box, use the Metered Demand field to specify the existing load.

220.88 New Restaurants. Set the Load Calculation Method to Restaurant, All Electric or Restaurant, Not All Electric to use this code section.

Part V. Farm Load Calculations

Farm load calculations are not included in Design Master Electrical.

Article 550 Mobile Homes, Manufactured Homes, and Mobile Home Parks

550.31 Allowable Demand Factors. Set the Load Calculation Method to Mobile Home Park to use this code section.

Set the number of mobile homes using the Mobile Homes field.

When circuiting, use the Marina / Mobile Home / RV load type for the load on each mobile home lot.

Article 551 Recreational Vehicles and Recreational Vehicle Parks

551.73 Calculated Load. Set the Load Calculation Method to RV Park to use this code section.

Set the number of recreational vehicle sites using the Recreational Vehicle Sites field.

When circuiting, use the Marina / Mobile Home / RV load type for the load on each recreational vehicle site.

Article 555 Marinas and Boatyards

555.6 Load Calculations for Service and Feeder Conductors. Set the Load Calculation Method to Marina or Marina with Sub-Meters to use this code section.

Set the number of receptacles using the Shore Power Receptacles field.

When circuiting, use the Marina / Mobile Home / RV load type for the load on the shore power receptacles. If multiple shore power receptacles are provided for an individual boat slip, set the Demand Factor to 1 for the largest receptacle load and set it to 0 for all the others.

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