• Problem:
  When an insulated joint is used to electrically isolate sections of pipeline, over-voltage protection of the joint insulation may be necessary. The insulation can fail, due to lightning or AC fault current, with potentially disastrous results. Arcing across the joint will cause insulation failure and possible ignition of flammable gases.
    
• Solution:
  A protection device connected across the insulated joint will limit the voltage to safe levels, and provide a conduction path around the joint, while maintaining cathodic protection. Products listed for use in hazardous locations will address the over-voltage problem while assuring safe operation.

To implement an insulated joint protection system, the following issues need to be examined to determine product selection and ratings:

1.  The maximum DC voltage present across the insulated joint
2.  Whether induced AC voltage is present at the site
3.  Examine AC fault current exposure
4.  Location of the device, and the resulting conductor length
5.  Is this site classified as a hazardous location?
6.  For mounting options, see data on each product page

Applicable Products

• Typical:
  PCR – for Ordinary, Div 2, or Zone 2 areas, mitigates induced AC voltage.
  OVP – for Ordinary, Div 2, Zone 2, or Div 1 areas; do not use with induced AC voltage.
    
• Alternate:
  PCRH – same as PCR, but for Div 1 areas.
  ISP – for Ordinary areas, where requirements include higher blocking voltage, high AC fault current ratings, or customization.

• Problem:
  Airports utilize underground piping to transport large amounts of jet fuel, and this critical infrastructure requires cathodic protection to prevent corrosion. Since cathodic protection systems utilize insulated joints to sectionalize the piping, arcing at insulated joints presents a hazard to system operation and personnel, whether due to AC fault current, lightning, or static buildup.
   
  A separate problem exists where the grounding conductor on motors or other electrical equipment on a cathodically protected pipeline shorts the CP system to the copper grounding system, resulting in inadequate levels of cathodic protection. While the grounding conductor is required by code, a means of addressing the CP current flow on this conductor is needed.
   
• Solution:
  Over-voltage protection of the insulated joints can be accomplished using Dairyland devices that are UL listed for hazardous locations. Most common is the model OVP, which was developed in conjunction with the US Army Corp of Engineers to meet their need for a listed Class I, Division 2 product. The OVP is specified by the Corp of Engineers for worldwide use for US military airport applications.
   
  Where grounding conductors affect the CP system, the Dairyland model PCR is most commonly used. The device is placed in series in the grounding conductor (and conduit if needed) to block the flow of DC current, while acting as a low impedance path to AC current. The devices are UL listed for meeting the electrical codes in the US and Canada for placement in a grounding conductor.

Implementation:
A. Insulated joint protection using an OVP

1. Select the OVP model with the FMFB mounting option, if using the flange bolts for mounting the brackets. For other mounting methods, see the OVP literature.
2. Specify the hole size needed for the FMFB mounting kit. This hole diameter should allow for the flange bolt and insulating sleeve, plus clearance. Usually this value is 1/8" larger than the bolt diameter.

Applicable Product:  OVP

 
B. Decoupling electrical equipment from ground

1. The AC fault current in the circuit should be compared to the product ratings.
2. The device is connected in series in the safety grounding conductor, with the negative connection to the cathodically protected structure, and the positive connection to the panel ground.
3. Additional comments are provided in the application article regarding decoupling electrical equipment.

Applicable Products: Typical: PCR – for Ordinary or Div 2 areas

Alternate: PCRH – for Div 1 areas

• Problem:
  When pipelines are in a common corridor with energized power lines, electric and magnetic fields can cause unwanted voltage to appear on the pipeline. This induced voltage requires low resistance grounding for mitigation, while cathodic protection demands complete isolation for the pipeline.
    
• Solution:
  DEI products provide continuous AC grounding for pipelines with induced voltage, while leaving the cathodic protection voltage unaffected. The device presents low impedance to alternating current and high impedance to direct current, and connects between the pipeline and a grounding system.

Mitigation designs for induced AC voltage are best done by specialists trained in the proper analysis techniques. Such analysis involves measurements and electrical modeling, using software developed for this task. While an overview of the issues involved is shown below, complete analysis may involve the use of such specialists.

Small projects can have reasonable estimates applied to determine product ratings and a basic system design. Examine the issues outlined below or call DEI for additional guidance.

To implement an induced AC voltage mitigation system, the following issues
need to be addressed.

1.  A suitable low resistance grounding system is needed
2.  The induced AC steady-state current flowing to ground needs to be known
3.  AC fault current exposure exists and should be estimated
4.  Is this site considered a hazardous location?
5.  Mounting the DEI device for above-grade or underground connections

• Problem:
  When a cathodically protected structure is tied into the site grounding grid, CP values may be unacceptably low, due to the bond between the site grounding system and the power company grounding system. The CP system attempts to protect the power company grounding system as well.
   
• Solution:
  The DEI model PCR can be installed by the power company at the transformer, to provide DC isolation and AC grounding between the two systems. The site CP system will not attempt to protect the power utility grounding system. This minimizes the CP current requirements and allows acceptable CP voltage for protection.

To implement a primary-to-secondary decoupling solution, the following issues need to be examined to determine product selection and ratings:

1. Verify that decoupling the bond between the utility grounding system and user grounding system results in a change in the CP voltage and current. Accomplish this by temporarily disbonding the grounding connections between the two systems, using appropriate safety practices. At a small facility, this can be accomplished by turning off loads, then disconnecting the neutral and/or grounding conductor from the panel. The same isolation can be accomplished by the power company at the transformer. Keep in mind that other utility services, such as telephone, also connect between primary and secondary grounding systems and will act as a bypass unless addressed.
     
2. Examine AC fault current exposure and select a rating in excess of the site conditions.
     
3. Confirm acceptance by the power company of the proposed isolation. Note: for certain wiring arrangements this type of decoupling can occur within the user’s electrical system.