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Residential Feeder Load Calculation Quick Start

Tuesday, July 22nd, 2014

This post shows you the settings necessary to do residential feeder load calculations in Design Master Electrical. It will help you avoid the most common errors customers encounter when first using the calculation.

Set the Load Calculation Method Correctly

Go to DM Electrical->One-Line Devices->Panel. Create a panel if you have not already.

Press the Feeder and Service Calculation Settings button.
Make sure Load Calculation Method is set to Default.
Press the Set Default button next to Load Calculation Method.
Choose the Load Calculation Method that you want to use for your project.

  • Dwelling Unit, Section III: Choose this to do a general feeder calculation using NEC 220.40 and following.
  • Dwelling Unit, Section IV: Choose this to do a feeder calculation using the optional dwelling unit feeder calculation using NEC 220.82.
  • Dwelling Unit, Existing: Choose this to do a feeder calculation using the optional existing dwelling unit feeder calculation using NEC 220.83.
  • Multifamily Dwelling: There are three different multifamily dwelling options. If there are multiple units, all three do a feeder calculation using the optional multifamily dwelling unit feeder calculation using NEC 220.84. The difference in the three choices is which calculation method is used for a single dwelling unit. You can use NEC 220.40 and following, NEC 220.82, or NEC 220.83.
Press OK.

All the panels and other one-line devices in your project will use the selected default Load Calculation Method.

If you choose a Multifamily Dwelling option, set the Multifamily Dwelling Units value. Set this at the panel furthest down the one-line. The number of dwelling units on upstream panels will be set correctly. For example, panel MDP feeds three panels–A, B, and C–that each serve a single dwelling unit. On panels A, B, and C, set the Multifamily Dwelling Units value to 1. On panel MDP, set the Multifamily Dwelling Units value to 0.

Set the Schedule Block Correctly

Stay in the Feeder and Service Calculation Settings dialog. If you are not already there, go to DM Electrical->One-Line Devices->Panel then press the Feeder and Service Calculation Settings button.

Make sure the Schedule Block is set to Default.
Press the Set Default button next to Schedule Blocks.
Choose a panel schedule that matches the Load Calculation Method set above. The default customization includes panel schedules for Panel with Phase Breakdown and Panel without Phase Breakdown.
Press OK.

All the panels and other one-line devices in your project will use the selected default Schedule Block.

Set Default General Lighting Circuit Value Correctly

Stay in the Feeder and Service Calculation Settings dialog. If you are not already there, go to DM Electrical->One-Line Devices->Panel then press the Feeder and Service Calculation Settings button.

Make sure the Default General Lighting Circuit Value is set to Default.
Press the Set Default button next to Default General Lighting Circuit Value.
Select No.
Press OK.

All circuits will be set to no be general lighting circuits by default.

Set Occupancy Areas Correctly

Stay in the Feeder and Service Calculation Settings dialog. If you are not already there, go to DM Electrical->One-Line Devices->Panel then press the Feeder and Service Calculation Settings button.

In the Occupancy Areas section, find the 3 VA / sf Occupancy Areas section. Set the 3 VA / NEC Table 220.42 Demand Area to the area of the dwelling unit.

Set General Lighting Circuit Setting on Circuits Correctly

Go to DM Electrical->Circuiting and Homeruns->Circuiting.

Connect devices or use the Set Fixed Loads button to set the loads on the circuits.

For circuits that have lighting connected to them, change the General Lighting Circuit value from Default to Yes. The load on these circuits will be ignored in the total panel load. It is assumed they are part of the general lighting load defined by the occupancy error specified for the panel.

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