PCRX Technical Information

About the PCRX

The Dairyland PCRX is a solid-state decoupling device commonly used in conjunction with cathodically protected structures.

The PCRX prevents the flow of direct current while simultaneously providing a grounding current path for steady state induced alternating current, if present. Steady state AC current of up to 45A rms can flow through the device with DC voltage applied within the operating voltage range. These products also provide over-voltage protection for both lightning and AC fault current conditions.

The PCRX provides the additional benefit of electronically camouflaging itself from interrupted surveys, including close interval surveys (CIS), preventing the device from contributing to errors in potential readings. Field testing has shown that interrupted surveys can sometimes be impacted by combinations of factors such as pipeline coatings, soil resistivity, and the capacitance of decouplers resulting in excessively electro-negative instant-off values. In most cases the PCRX completely solves this problem. The PCRX camouflages itself to overcome capacitive effects ensuring accurate and timely potential measurements. It does this without sacrificing the rugged over-voltage, AC mitigation, CP isolation, and safety grounding of Dairyland’s standard decoupling products. 

Common Applications

AC Voltage Mitigation

As an AC mitigation device, the PCRX can collapse the steady-state voltage between the connected points to a negligible level by providing continuous AC grounding for pipelines affected by AC induction while leaving cathodic protection unaffected.

Decoupling Electric Equipment Grounding Systems

When electrical equipment is mounted on a cathodically protected structure, the PCRX can provide DC isolation with fault rated AC continuity. As grounding codes apply, the PCRX is listed by UL for meeting the requirements of an effective AC grounding path per U.S. and Canadian electric codes.

Isolation Joint Protection

Isolation joints often need over-voltage protection against lightning and AC fault exposure, and in some cases, steady-state induced AC voltage. Due to the small clearance between opposite sides of the isolation flange, a protective device must provide a low clamping voltage, including the voltage effects of the conductors or bus bars used to connect the product.

Electrical Ratings

AC Fault Current Ratings

Some applications may have conditions where an over-voltage device such as the PCRX is subject to momentary fault current. For this reason, the PCRX was designed to have AC fault current carrying capability. The PCRX will limit the voltage between its connection points to less than 18V peak under the maximum fault current ratings listed below.

Fault current ratings are offered with the following current-time relationship:

AC Fault Current Ratings (Amps AC-RMS Symmetrical)

50/60 Hz Cycles	5kA Model	10kA Model	15kA Model
3	6,800	15,000	27,000
10	5,700	12,000	21,000
30	5,000	10,000	15,000

Note: Verify that the PCRX fault current capability exceeds site conditions. For more information on determining fault current exposure, view our web article: Determining AC Fault Current.

State AC Current Ratings

This rating represents the maximum steady-state AC 50/60Hz current that is allowed to flow through the device while still blocking the flow of DC current. Exceeding this rating can result in damage to the PCRX.

Continuous AC Current Ratings

0 to 45A RMS

 

The most typical application where a PCRX may be required to block DC current while simultaneously carrying steady-state AC current occurs when a pipeline is in the same corridor as an electrical transmission line, resulting in steady-state AC induction voltage. The PCRX can mitigate this voltage by providing a low AC impedance path for AC current to flow to ground while simultaneously preventing the flow of DC current.

Note that unlike other decouplers, PCRX units cannot be installed in parallel to achieve a steady-state current rating above 45A AC-rms at a designated installation location.

Under an AC fault or lightning current condition, the impedance of the PCRX momentarily becomes virtually zero. For more information on steady-state current view our web article: Measuring Steady-State AC Current.

PCRX Blocking Voltage Rating

The PCRX employs proprietary technology to provide the additional benefit of electrically camouflaging itself from interrupted surveys without requiring an external power source. The unique operating characteristics of the PCRX create a distinct difference between the device’s fixed blocking voltage and its allowable DC operating voltage range. The fixed blocking threshold voltage is the total voltage limit across the PCRX terminals (Volts ACpeak + Volts DC) while the DC Operating voltage range is the allowable DC voltage across the PCRX terminals, after considering the AC voltage present for the given AC current.

The blocking voltage threshold is the voltage at which the device will go into conduction and shunt all current through the PCRX, such as during a fault or lightning event. It is this blocking voltage threshold that is identified via the product model designation (-5.5V/+2.5V or -4.5V/+3.5V are the standard offerings).

Generally, a -5.5V/+2.5V would be selected for use with a copper mitigation system while the -4.5V/+3.5V would be for use with a zinc mitigation system or an isolation fitting with CP on both sides. The operating voltage is the allowable range of DC voltage across the device’s terminals while still blocking DC current and simultaneously conducting any steady state AC that is present.

The operating voltage is a narrower range than the blocking voltage threshold. Select the appropriate blocking threshold per guidance in Appendix A. Figure 1 shows an example of current flow before and after this DC threshold is reached in a -4.5V/+3.5V configuration.

Lightning Impulse Current Rating

All models have the same lightning surge current rating which is shown in the following table:

Ligntning Impulse Current Rating

Peak Amperes: 100kA

8×20 microsecond waveform

Product Features

Solid-State Design

The PCRX is built with proven solid-state components which have an instantaneous response with respect to voltage, thereby initiating voltage clamping immediately when the voltage attempts to exceed the blocking level selected.

Fail-Safe

An important safety feature of the PCRX is that if subject to AC fault current or lightning surge current in excess of its ratings such that failure occurs, failure will occur in the shorted mode. In the shorted mode, the unit can carry greater than rated fault current or lightning surge current and still provide an effective grounding (or conducting) path.

Enclosure

The PCRX enclosure is made of  epoxy powder-coated 304 stainless steel suitable for outdoor non-submersible applications and is rated NEMA 4X and IP66.

Terminals

Single-hole compact  spade terminal connectors are standard.

PCRX terminals have preinstalled 1/2” stainless hardware (bolts, nuts, washers). See Accessories for various attachment options.

Polarity / Electrical Connection

Polarity marks (+) and (-) are provided near the terminals to aid in proper installation. Connect the (-) to the structure with CP or more negative structure and the (+) to the ground bed, or more positive, system.

Note: The positive terminal is bonded internally to the metallic enclosure.

Size and Weight

Refer to outline drawings for dimensional data. Packaged weight is approximately 35 pounds (16kg).

Number of Operations

Virtually unlimited under maximum ratings, provided the operations are not immediately repetitive.

Energy Requirements

None. The PCRX does not require an external power source.

Mounting Options

The PCRX is made to mount above grade on a flat surface (e.g., a wood post, unistrut, panel) with up to 5/16” bolts furnished by the user. Pedestal mounting is also an option.

Note: Because of the internal bond between the enclosure and positive terminal, mount the PCRX on a structure not in contact with the cathodically protected structure.

Additional Data

Instant-Off Waveform comparison
Standard Decoupler vs. Decoupler Disconnected vs. PCRX

I-V Characteristic of 3.5V PCRX at +20C/65C