Decoupling Tank Grounding Systems

Decoupling Tank Grounding Systems

Problem:

Local tank grounds, as well as grounding conductors for electrical equipment, will tie the cathodically protected tank to additional in-earth structures, requiring excessive CP current. However, grounding must be available for lightning protection. Further, electrical codes require grounding conductors for electrical equipment associated with the tank, such as a motor operated valve, to remain available for over-voltage protection and clearing AC faults.

Solution:

All Dairyland products provide excellent over-voltage protection for lightning effects, as well as AC faults, and block cathodic protection current that would otherwise flow to driven ground rods. To address electrical equipment grounds, a Dairyland decoupler certified for use in an equipment grounding conductor is an authorized method of providing DC isolation and simultaneous AC grounding for motors and other equipment. In the case of a motorized valve, this eliminates the need for insulated joints on either side of the valve. See the schematic of a sample installation. Insulated joints associated with tank sites can also be protected using Dairyland products.

To implement an equipment/tank isolation system, the following issues need to be examined to determine product selection and ratings:

  1. The maximum DC Voltage present between the structure and ground
  2. Whether induced AC voltage is present at the site
  3. Examine AC fault current exposure
  4. Is this site classified as a hazardous Location?
  5. 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. For insulated joint protection, see Application Note #1.