Wire sizing
Two different runs to size: the single-phase feeder into the converter, and the three-phase output to your machines. Pick the one you are working on.
Single-phase input wiring
Sizing the feeder, breaker and disconnect from your service to the converter panel.
Three-phase output wiring
Sizing the run from the converter to a sub-panel or directly to each machine.
How sizing is decided
- 1Start from nameplate current, not horsepower alone. The idler motor and each machine have their own full load amps.
- 2Size conductors for the continuous load with the usual code margin, then choose overcurrent protection that allows motor inrush.
- 3Add for distance. Voltage drop, not ampacity, drives most upsizing in a shop.
- 4Account for conditions of use: ambient temperature, conduit fill, and the terminal temperature rating of your breaker and lugs.
- 5Run a properly sized equipment grounding conductor to the panel, the idler frame and every machine.
For runs longer than about 100 ft, increase the conductor one size for every additional 100 ft to keep voltage drop under 3%.
These tables are planning aids only. Final conductor and overcurrent sizing must be determined by a licensed electrician from your actual nameplate values, run length and installation conditions under the National Electrical Code and local code.