Estimates only. These results may be wrong for your specific installation, and they are not engineering or code-compliance advice. Check every result against the code that applies to you and with your local inspector (AHJ) before you install anything. Terms of Service

Lay out a motor branch circuit, or check one you've designed. Wire inside the panel follows common panel wiring practice: internal wiring at 100% of full-load current, the field terminal and wiring to the motor at 125%.

Build a circuit Check my design

Motor

Starting method Phase Voltage Horsepower Temperature column Motor code letter and duty From the nameplate. Heavy duty: jogging, plugging, or over 25 starts an hour. Picks the column of the breaker maker's selection table.

Include a starter and overload

How this is worked out

One-line diagram

How the motor circuit builder works

Describe a motor and how it starts and the builder lays out the branch circuit as a one-line diagram, with the breaker, the wire inside the panel and the wire out to the motor labeled. You can also type in your own design and have it checked.

Steps

Choose the starting method: across the line, VFD or soft starter.
Choose phase, voltage and horsepower, and the temperature column for the wire.
Choose the motor's code letter and duty (normal starts, heavy duty, or code letter F to V). For a drive, pick it from the list of PowerFlex drives to use its listed protection, or enter its rated input and output amps.
Press Build circuit. The diagram appears with sizing call-outs and a section that shows how each value was worked out.
Use Check my design to enter your own breaker and wire sizes and see how they compare.

Example

Inside the panel the wire is sized at 100% of the full-load current, and the field terminal and the wire to the motor at 125%, so the same motor shows two different wire sizes on the diagram when the table breaks between them.

Questions

Is the diagram a drawing I can submit?: No. It is a quick sketch to help you think and talk about the circuit. Final drawings and sizing are your responsibility.
Why are there two wire sizes?: Wire inside a panel and field wiring follow different practices, so the tool sizes them separately.
Why does the breaker change with duty?: Breaker makers publish separate selections for normal starts, heavy duty or energy-efficient motors, and higher locked-rotor code letters. The tool shows the one for your choice and never goes above the code maximum.
Where do drive and starter numbers come from?: From what you enter. For a drive, use the ratings on its nameplate and follow the manufacturer's installation instructions.

The code references on this page are pointers, not a substitute for the code. NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association (NFPA). WireAndWidgets is not affiliated with or endorsed by NFPA. Rules differ by edition and by local amendment, so check the code your inspector (AHJ) enforces before you build or install anything.

Motor circuit builder