The National Electric Code (NEC) has a number of rules for determine the wire size required to feed a load. Design Master Electrical incorporates most of these rules automatically. Branch circuits and panel feeders are sized differently.

Branch Circuits

The NEC requires that branch circuits be sized to serve 125% of the continuous load and 100% on the noncontinuous load (NEC 210.19). Design Master Electrical includes an option to calculate the branch circuit load at 125% of both the continuous and noncontinuous. This is a more conservative approach than what the NEC requires. You can change this setting using the “Size breaks to 100% of noncontinuous load” option in “DM Electrical->Customization->Options.”

Here are how the load types are broken down between continuous and noncontinuous:

Continuous

• Lighting
• Motor (NEC 430.24)
• Continuous
• Heating (NEC 424.19)

Noncontinuous

• Receptacle
• Noncontinuous
• Kitchen
• Diverse

When you create a custom load type, you specify whether it should be treated as a continuous or noncontinuous load for branch circuit sizing. Do this using the “Custom Load Type: Load Type” option in “DM Electrical->Customization->Options.”

All motors are considered continuous at the branch circuit level. NEC 424.19 allows you to treat the largest of continuous and the rest as noncontinuous. If that is required for your design, you will need to manually downsize the motor breaker and wires.

Feeders

Design Master Electrical does not automatically size feeders. The software calculates the total load on a panel, but you have to select the final size for the feeder.

Lighting

The calculated lighting load is equal to 125% of the connected lighting load.

Motors

The calculated load on the largest motor on the panel is equal to 125% of the motor load. All other motors on the panel are sized at 100% of their connected load. The largest motor is based upon all the motors connected to the panel and any panels it feeds.

Receptacles

The receptacle load is calculated at 100% up to 10 kVA and 50% above that.

Continuous

Continuous loads are calculated at 125% of the connected load.

Heating

Heating loads are calculated at 100% of the connected load.

Noncontinuous

Noncontinuous loads are calculated at 100% of the connected load.

Kitchen

Kitchen loads are calculated based upon the number of pieces of kitchen equipment. Each receptacle or equipment connection is counted as a separate piece. The diversity factor is based upon NEC 220.56.

Diverse

Diverse loads do not have a default calculated load. You specify the diversity factor for the load when you create it that is used for the calculated load.

The layer that circuit loops and homeruns are inserted on by default is controlled by the “Default Circuit Layer System” setting in “DM Electrical->Customization->Options->Edit Project List”.

The original setting for this option is “Same as One Line Device”. With this setting, the loops use the layer system of the panel or switchboard, not the device they are connected to.

You can also change this setting to be a specific layer system. If you do this, then the loops will use the layer system you select, not the panel layer system and not the device layer system.

This option controls the default setting. It is also possible to change the layer system used by a specific circuit. To do this, open the circuiting dialog using the “DM Electrical->Circuiting and Homeruns->Circuiting” command. Select the circuit you want to change the layer of. On the right side the “Layer System” will be listed. Choose the layer system you want and press the “Save Fixed” button.

If you change your default layer system or change the layer system of a circuit that already has loops inserted, you can use the “DM Electrical->Utilities->Coordinate Drawings and Database” command to update your drawing.

To model a light fixture with multiple heads for point-by-point photometrics, it is necessary to insert each head as a separate light in Design Master Electrical.

In the “Light Fixture Project Schedule”, you will want to create a fixture that represents a single head. Choose an appropriate graphic for the single head. You can uncheck the “Include in Schedule” toggle to have this fixture not be displayed in the schedule you insert on the drawing.

If you want to circuit a single fixture that has the total light load on it, you will need to create another fixture to represent that. This fixture you will want to include on the schedule you insert on the drawing.

Insert one fixture on the drawing for each head. Insert a fixture to be circuited also, if appropriate. These fixtures might end up stacked on top of each other, depending upon how your fixtures are arranged on the drawing.

When doing outdoor photometrics or indoor egress photometrics, you can aim light fixtures at a specific point on the ground using the “DM Electrical->Point-by-Point Photometrics->Aim Light Fixture” command.

This command is helpful when trying to aim lights on a athletic field or trying to aim emergency lights to make sure the path is properly illuminated.

When doing indoor lighting level calculations, a coefficient of utilization (CU) is calculated to determine the amount of light in the room.

If an IES file is attached to the fixture, it is used to calculate the CU if possible. Not all IES files has sufficient information to calculate the CU. This calculation depends upon the wall, ceiling, and floor cavity reflectance values specified in the room definition.

If the IES does not have sufficient information to calculate the CU, or no IES file is attached to the fixture, a default value of 0.7 is used.

The CU that is displayed also includes the dirt depreciation factor set in the room and the lamp depreciation set in the light fixture schedule.

When you are doing outdoor photometrics, you often do not want the foot candle levels to be displayed inside the building outline drawn with the light-obstructing objects. The extra 0’s both clutter the drawing and are included when calculating the statistics, resulting in incorrect values.

If the boundary is drawn using the “Insert Light-Obstructing Line” command, foot candle levels will appear inside the building.

If the boundary is drawn using the “Insert Light-Obstructing Rectangle” or “Insert Light-Obstructing Shape” commands and the starting elevation is 0, foot candle levels will not appear inside the building.