Top-10 Questions About Decouplers

Q U I C K   L I N K S

What is the difference between a Decoupler and an Over-Voltage Protector?
When do I need a Dairyland Decoupler?
How do I test a decoupler to know if it is working?
What is the difference between a PCR and an SSD?
Which products are rated for hazardous locations?
How do Dairyland decouplers compare to competing technologies?
What polarity should be used to connect a decoupler?
What is a “voltage threshold”? And how do I know that my decoupler has the correct voltage threshold for my application?
What should the spacing between decouplers be for AC Mitigation applications?
How do I spec a product for an insulated joint?

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Dairyland technical support personnel work tirelessly to ensure all your needs are met when it comes to products, applications, and general support. Below, we have compiled a list of frequently asked questions regarding Dairyland decouplers and their various applications. This resource will also guide you to related articles in our Knowledge Base for further reading.

Dairyland decouplers keep workers and valuable assets safe from AC faults, lightning, and induced AC voltage, all while optimizing cathodic protection systems. We hold ourselves to a very high Always Rugged standard to ensure Dairyland products meet all critical performance requirements, provide fail-safe operation, and address hazardous location needs to guarantee longevity and safety.

Our tech support team is available during our normal business hours and can be reached via phone (608-877-9900) or email (TechSupport@dairyland.com).

 

What is the difference between a Decoupler and an Over-Voltage Protector?

Decouplers (PCR, PCRH, PCRX, and SSD) are commonly used to isolate cathodically protected structures from other equipment grounding systems, enhancing the cathodic protection system’s performance. They also perform a function of safely grounding induced AC, fault current and lightning. Over-Voltage Protectors (OVP and OVP2) provide the same DC isolation and protection from fault current and lightning but are not designed to address induced AC current.

Therefore, the first question to ask when selecting a Dairyland product family is whether there is (now or could be in the future) any induced AC voltage present. Induced AC commonly occurs on structures near overhead powerlines. If the answer is yes, or if you are unsure, you should select a decoupler to address any present or future issues with induced AC.

Additional Resources: “What Are Solid-state Decouplers and How Are They Used?” and “Over-Voltage Protection: The Critical Differences Between Spark Gaps and DC Decouplers.”

 

When do I need a Dairyland Decoupler?

The short answer is that a decoupler can be used for a variety of purposes and applications. Most frequently, they are installed when it is desirable to isolate DC current (CP current) while simultaneously grounding AC fault current and lightning current.

DC Decouplers are commonly used for applications such as:

• Isolating electric equipment from grounding systems, while still meeting electrical codes for safety
• Insulated joint over-voltage protection
• Connecting a cathodically protected pipeline to an AC mitigation system
• Tying a cathodically protected pipeline to a gradient control mat
• Grounding of power cable sheaths/casings to substation grounding systems
• Separating a facility with CP from power utility grounding systems beyond the transformer

Additional Resource: “AC Mitigation and Cathodic Protection: How Decouplers Make a Difference”

 

How do I test a decoupler to know if it is working?

A simple, indirect way to test a decoupler is through a standard pipe-to-soil reading. If your test shows acceptable CP levels, then the device is functioning properly. Decouplers are designed to block DC current, therefore acceptable cathodic protection readings reflect an operational Dairyland device.

For more detailed testing, please refer to our website’s tech articles: “Indirect Testing” & “Direct Testing.”

 

What is the difference between a PCR and an SSD? 

PCRs and SSDs provide the same functions, and the main differences are in the ratings, package size, and cost.

• PCR AC fault ratings: 3.7 kA, 5 kA, 10 kA, and 15 kA.
• SSD AC fault ratings: 1.2 kA, 2.0 kA, 3.7 kA, and 5 kA.

Dairyland’s SSD was created as a more compact unit some years after the PCR. They share AC fault current capabilities, but the SSD was developed primarily for handling lower AC fault conditions. These units have identical hazardous location ratings, suitable for Division 2 and Zone 2 locations. PCR enclosures have either a NEMA 4X (IP66) rating or an optional NEMA 6P rating. SSDs enclosures have an IP68 rating (similar to NEMA 6P) that is rated for submersion up to two meters.

Additional Resource: “What if Decouplers Didn’t Exist?”

 

Which products are rated for hazardous locations?

PCR, PCRX, SSD, and OVP2 are all rated for use in areas with a Class I, Division 2 or Zone 2 classification. Class I, Division/Zone 2 units are suitable for most common applications, and these are Dairyland’s most frequently used devices.

PCRH and OVP are rated for use in areas with a Class I, Division 1 or Zone 1 classification. These units can still be used in any application with lesser requirements, such as Class 1, Division/Zone 2 installations.

Additional Resource: “Understanding Hazardous Locations”

 

How do Dairyland decouplers compare to competing technologies?

As a corrosion professional, your ideal applications keep your personnel safe and your system running efficiently. As an installer, you want tech that is easy to install and is maintenance-free. No matter your position, we know you are looking for solutions that address your various needs.

There are several devices on the market that attempt to resolve one or more of these concerns. However, maintenance needs, limited lifespans, and safety concerns all come attached to their price tags. Dairyland decouplers offer a solution to all your CP isolation and over-voltage protection needs. Because of their proven reliability, Dairyland’s solid-state decouplers are the smart choice over other DC isolation devices. Long-term, you will save maintenance labor and material costs by installing Dairyland devices. You will also mitigate risk to your equipment and personnel.

In addition to manufacturing industry-leading products, we pride ourselves on providing reliable technical support. Contact us any time.

Additional Resources: “Dairyland Decouplers vs. Competing Technologies” and “Dairyland OVP Devices vs. Competing Technologies”

 

What polarity should be used to connect a decoupler?

In general, the negative terminal connects to the more negative structure, and vice versa. Therefore, generally the + (Positive) goes to the ground connection and – (Negative) goes to the structure with CP.  Across an insulated joint, where one side has CP and the other is grounded, connect negative to the protected side, and positive to ground. For an insulated joint with CP on both sides, select a symmetrical device, which is typically -2V/+2V, and then polarity is irrelevant.

Additional Resource: “Polarity Matters – Labels On Your Decoupler”

 

What is a “voltage threshold”? And how do I know that my decoupler has the correct voltage threshold for my application?

A decoupler’s voltage threshold is the voltage range supported between its terminals before direct current conduction. This is different from the industry measurement of “structure to soil” voltage, which is measured to a reference cell. The key value to measure is the difference between the two points a decoupler would be connected (pipe and ground) and compare that value to the negative threshold value.

For example, if a pipe-to-soil reading of -2V were obtained, and the reading from a grounding system to the same reference cell was -0.3V, then the decoupler connected between this pipe and grounding system would be exposed to -1.7V, which is the difference between the two readings. This assumes that the standard practice was used with decoupler negative terminal connected to the more negative structure (the pipeline) and positive to the grounding system. If the decoupler had a -3/+1V threshold, we compare the -1.7V reading to -3V value and find it acceptably below that threshold. Note that a -2/+2V threshold would have worked fine in this example as well. If the measured value were above the threshold, then the decoupler would be in full conduction and not block CP current. Standard Dairyland decoupler thresholds cover most pipeline situations.

A specific case that should be examined is where proximity to a rectifier results in elevated pipeline voltage that could approach the decoupler threshold and in that case one might consider the 3, 4, or 6 volt negative threshold to address this.

Additional Resources: “Understanding Voltage Threshold Ratings” & “Voltage Threshold Simulator”

 

What should the spacing between decouplers be for AC Mitigation applications?

Studies and testing should be conducted to accurately place Dairyland units for optimum AC mitigation and over voltage protection. Mitigation consultants are available to perform software modeling for optimal AC mitigation. Dairyland does not perform AC mitigation planning or studies. However, when we talk to mitigation designers regarding spacing, we have found that they often space these every ½ mile, presuming no pipeline or powerline changes in between that would cause a voltage spike. For example, whenever the pipeline or powerline change position relative to each other there will be a change in the magnetic field and a resulting voltage rise there, and a decoupler will be located near that change. Don’t forget other pipeline features such as insulated joints in the right-of-way that should be protected with a decoupler, as well as casings. AC mitigation design is a specialized field, and there are many factors that affect a design.

Additional Resource: “Decoupler Spacing for AC Mitigation Projects”

 

How do I spec a product for an insulated joint?

First, determine whether steady-state AC is present on either side of the joint.

• If AC is present, use PCR, PCRH, PCRX, or SSD.
• If AC is not present, use OVP or OVP2.

It is safer to assume that AC is present or could be in the future. Situations where AC is not likely are limited to airport fueling systems, and insulated joints interior to large facilities. Use caution, as AC induction on pipelines may require decouplers (SSD, PCR, PCRH) applied to a series set of insulated joints to mitigate AC to a station grounding system, only then allowing other insulated joints within a facility to utilize other Dairyland devices such as the OVP or OVP2. Due to complexity of stations, it is best to consult Dairyland staff for guidance.

Second, if the joint is in a Class I, Division 2 location, use models PCR, SSD, or OVP2 (most locations are Div 2/Zone 2). If the joint is in a Class I, Division 1 location, only use models PCRH or OVP.

Third, once the correct decoupler or over-voltage device is selected, choose the correct voltage threshold based on data (DC levels) collected from the pipeline. Typically, the standard ratings of -3/+1 or -2/+2 V are adequate. The -2/+2 (“symmetrical”) rating can be used where CP is present on both sides of a joint, or for CP present on one side of the joint only. The -3/+1 is generally only used where there is CP on one side of the joint and the other side is grounded. Remember to connect the negative terminal to the more negative, or cathodically protected, side.

Additional Resource: “Over-Voltage Protection: The Critical Differences Between Spark Gaps and DC Decouplers”

 

Bonus Additional Resources Regarding the MEGA Rule:

• “PHMSA Mega Rule Explained and How Dairyland Can Help You“
• “Understanding the Mega Rule: Accurate Close Interval Surveys“
• “Understanding the Mega Rule: Interference Mitigation“
• “Understanding the Mega Rule: RMV Installation Best Practices“

 

Should you have an eleventh or twelfth question, do not hesitate to contact our team at TechSupport@dairyland.com.