Service Home 3-Phase Input Power Configurations - RD0084
Last updated: 10/28/2025

3-Phase Input Power Configurations - Reference Guide

RD0084

Revision A - 10/2025

Electrical Safety

 DANGER: Working with the electrical services required for CNC machines is extremely hazardous and can result in serious injury or death.

Before connecting line wires to the CNC:

  • Turn off all power to the machine at the source.
  • Perform a Lockout-Tagout (LOTO) procedure to ensure the power remains off during service.
  • Verify that power has been disconnected by using an AC voltage detector on all incoming lines.

If you are uncertain about how to safely disconnect power or perform LOTO procedures:

  • Do not proceed.
  • Contact qualified personnel or obtain appropriate assistance before continuing.

Failure to follow these precautions may result in electrical shock, equipment damage, or fatal injury.

 Danger: Before beginning any work inside the control cabinet, verify that the High Voltage indicator light on the 320V Power Supply / Vector Drive has been off for a minimum of five (5) minutes. This waiting period ensures that residual voltage has dissipated and reduces the risk of electric shock.

Certain service procedures involve high-risk electrical components and may pose serious injury or fatality hazards. Technicians must not attempt any procedure unless they have a complete understanding of the steps involved and the associated risks.

If there is any uncertainty regarding a procedure, contact your Haas Factory Outlet (HFO) to arrange for a qualified service technician.

Input Power Configurations

Center Grounded Wye Configuration

FOR A CENTER GROUNDED WYE INPUT POWER CONFIGURATION:

The order of where each leg is connected to the machine's main breaker does not matter for this configuration of input power. 

Connect the legs to the L1, L2, and L3 terminals on the main breaker. Connect the ground to the terminal on the panel in the control cabinet. 

After all legs are connected, power on the machine and check the PHASE DETECT indicator on the PSUP PCB. If the Reversed amber LED is ON, power off the machine, disconnect from main power, and swap the legs in the L2 and L3 terminals on the main breaker.

Check the voltage reading from leg to leg and leg to ground. The table lists the common leg-leg voltages and the corresponding leg-ground voltages for a center grounded wye input power configuration.

Measurment Voltage Readings
L1 - L2 208 240 400 480
L1 - L3 208 240 400 480
L2 - L3 208 240 400 480
L1 - GND 110 - 125 125 - 145 208 - 243 250 - 290
L2 - GND 110 - 125 125 - 145 208 - 243 250 - 290
L3 - GND 110 - 125 125 - 145 208 - 243 250 - 290

Line Grounded Wye Configuration

FOR A SINGLE LEG GROUNDED WYE INPUT POWER CONFIGURATION:

The order of where the legs are connected to the Haas machine DOES matter.

Connect the grounded leg to the L1 terminal in the main breaker.

The image below shows the L1 line of the incoming power is the grounded leg. So, L1 is the leg connected to the L1 terminal on the Haas machine.

After all legs are connected, power on the machine and check the PHASE DETECT indicator on the PSUP PCB. If the Reversed amber LED is ON, power off the machine, disconnect from main power, and swap the legs in the L2 and L3 terminals on the main breaker.

Check the voltage reading from leg to leg and leg to ground. The table lists the common leg-leg voltages and the corresponding leg-ground voltages for a single leg grounded wye input power configuration. Use these voltage readings to determine which leg is the grounded leg from the input power.

Measurment Voltage Readings
L1 - L2 208 240 400 480
L1 - L3 208 240 400 480
L2 - L3 208 240 400 480
L1 - GND 0 0 0 0
L2 - GND 208 240 400 480
L3 - GND 208 240 400 480

High Leg Delta Configuration

FOR A HIGH LEG DELTA INPUT POWER CONFIGURATION:

The order of where the legs are connected to the Haas machine DOES matter.

Connect the "high leg" to the L1 terminal in the main breaker.

The image below shows the L2 line of the incoming power is the "high leg". So, L2 is the leg connected to the L1 terminal on the Haas machine.

After all legs are connected, power on the machine and check the PHASE DETECT indicator on the PSUP PCB. If the Reversed amber LED is ON, power off the machine, disconnect from main power, and swap the legs in the L2 and L3 terminals on the main breaker.

Check the voltage reading from leg to leg and leg to ground. The table lists the common leg-leg voltages and the corresponding leg-ground voltages for a high leg delta input power configuration. Use these voltages to determine which leg is the "high leg" from the input power.

Measurment Voltage Readings
L1 - L2 208 240 400 480
L1 - L3 208 240 400 480
L2 - L3 208 240 400 480
L1 - GND 104 120 200 240
L2 - GND 180 208 346 416
L3 - GND 104 120 200 240

Corner Grounded Delta Configuration

FOR A CORNER GROUNDED DELTA INPUT POWER CONFIGURATION:

The order of where the legs are connected to the Haas machine DOES matter.

Connect the line connected to ground to the L1 terminal in the main breaker in the machine.

The image below shows the L1 line of the incoming power is the grounded leg. So, L1 is the leg connected to the L1 terminal on the Haas machine.

After all legs are connected, power on the machine and check the PHASE DETECT indicator on the PSUP PCB. If the Reversed amber LED is ON, power off the machine, disconnect from main power, and swap the legs in the L2 and L3 terminals on the main breaker.

Check the voltage reading from leg to leg and leg to ground. The table lists the common leg-leg voltages and the corresponding leg-ground voltages for a corner grounded delta input power configuration. Use these voltages to determine which leg is the grounded leg from the input power.

Measurment Voltage Readings
L1 - L2 208 240 400 480
L1 - L3 208 240 400 480
L2 - L3 208 240 400 480
L1 - GND 0 0 0 0
L2 - GND 208 240 400 480
L3 - GND 208 240 400 480

Open Leg Delta Configuration

FOR A OPEN LEG DELTA INPUT POWER CONFIGURATION:

The order of where the legs are connected to the Haas machine DOES matter.

Connect the line connected to ground to the L1 terminal in the main breaker in the machine.

The image below shows the L1 line of the incoming power is the grounded leg. So, L1 is the leg connected to the L1 terminal on the Haas machine.

After all legs are connected, power on the machine and check the PHASE DETECT indicator on the PSUP PCB. If the Reversed amber LED is ON, power off the machine, disconnect from main power, and swap the legs in the L2 and L3 terminals on the main breaker.

Check the voltage reading from leg to leg and leg to ground. The table lists the common leg-leg voltages and the corresponding leg-ground voltages for an open leg delta input power configuration. Use these voltages to determine which leg is the grounded leg from the input power.

 Note: An open-leg delta configuration is susceptible to causing power supply alarms on some Haas machines. If you suspect incoming power could be the cause of the alarm then make sure that the grounded leg is connected to the L1 terminal of the main breaker on the machine.

Measurment Voltage Readings
L1 - L2 208 240 400 480
L1 - L3 208 240 400 480
L2 - L3 208 240 400 480
L1 - GND 0 0 0 0
L2 - GND 208 240 400 480
L3 - GND 208 240 400 480