Decoupling Electric Equipment Grounding Systems
Electrical equipment, such as motor operated valves, on a cathodically protected structure requires safety grounding according to the electrical codes, however a direct bond will cause a short-circuit on the CP system. Likewise, tanks with electrical equipment can be affected by the bond to ground.
Using a DEI product certified for use in a safety grounding conductor is an authorized method of providing DC isolation and simultaneous AC grounding for motors and other equipment. In the case of a valve motor, this eliminates the need for insulated joints on either side. Instead, the motor is grounded via the DEI isolation device. Certified (listed) products are needed for this application, to comply with electrical codes. See the schematic of a sample installation.
To implement an equipment/tank isolation system, the following issues need to be examined to determine product selection and ratings:
- The maximum DC Voltage present between the structure and ground
- Whether induced AC voltage is present at the site
- Examine AC fault current exposure
- Is this site classified as a hazardous Location?
- Install the device in series in the grounding conductor, and determine that there is not an electrical bypass around the device.
See Application Note #2 for a full review of this application.