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What is the electrical code or regulation for grounding a disconnected HV motor, just for reference purposes?

Hi Karo,

Thank you for your question regarding the grounding of disconnected High-Voltage (HV) motors, it is our pleasure to help.

There are two major concerns when dealing with high-voltage motors; capacitive discharge and inductive currents.  Often high voltage motors can hold and store a tremendous amount of electrical energy in its windings.  When the power is shut off that energy remains in the motor and must be discharged to make it safe for maintenance workers.  This hazard is called Capacitive Discharge and is technically a Touch-Voltage hazard as the current and voltage levels can easily exceed safe fibrillation current levels for the human heart. 

The second concern is Inductive or Induced Currents.  The feed wires for the inactive motor are often within close proximity to other active high-voltage motors.  The electrical energy from the active wires feeding other high-voltage motors can easily induce hazardous energy into the inactive wires of your isolated motor, charging the motor over time and causing another unsafe Touch-Voltage hazard, even after the original discharging.

Here is a previous blog on the same subject that may be of assistance to you:


Basically, you need to properly lock-out your HV motor, discharge the windings, and then ground all 3 phase wires before conducting any maintenance on the motor.

The main regulation governing these safety procedures is Title 29 of the Code of Federal Regulations Parts 1910 (29 CFR 1910.303), and Title 30 of the Code of Federal Regulations Parts 18 and 75 (see 30 CFR 75.814 Electrical Protection).  There are other codes and regulations as well, such as NFPA 70E Standard for Electrical Safety in the Work Place.  In the state of California there is the California Code of Regulations, 8 CCR Subchapter 5, Group 2, “High Voltage Electrical Safety Orders”.   Additionally there is the ASTM F 855-97, Standard Specifications for Temporary Protective Grounds to Be Used on De-energized Electric Power Lines and Equipment, and the IEEE 1048-2003, IEEE Guide for Protective Grounding of Power Lines, that may be of interest to you.  This is by no means a complete list of codes and regulations, but hopefully this will get you started.

Feel free to give one of our engineers a call if you have any further questions.

Best regards,

The Engineering Team at E&S Grounding Solutions


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