Decoupler Isolation Switches
Addresses Issues Such As:
- Isolation of high frequency signals from locators and coating defect instrumentation
- Decoupler isolation from close interval survey (CIS) operations
- Decoupler testing
Field InstallationIsolation Switches are suitable for field installation to any Dairyland model PCR* or SSD decoupler with a Dairyland pedestal. SWX-100-ENCL models can be factory assembled and delivered ready for installation if all required components are purchased.
* SW-50-XX switches not for use with PCR models rated 80A continuous. Use SWX-100 models.
Model Number Information
Mechanical switches designed to mount inside Dairyland fiberglass pedestals or as a standalone.
SW-50-SSD - For SSD with MTP Pedestal
SW-50-PCR - For PCR with MTP Pedestal
SW-50 - For SSD or PCR without MTP Pedestal
SWX-100-PED - For external pedestal mounting with SSD or PCR
SWX-100-ENCL - For PCR or SSD up to and including 10kA models, installed in a general purpose enclosure
Installation Instructions for Discontinued Pedestal MTP-42
SW-50 (For in-service SSD or PCR, not installed in a Dairyland Pedestal)
The PCR has been tested by Nationally Recognized Testing Laboratories (NRTLs) for compliance to independent standards in its operation, ratings, and construction. This includes compliance to standards for:
UL (United States) and C-UL (Canada) listing for:
- Providing an "effective ground-fault current path" as defined in NFPA 70 (US National Electrical Code - NEC), Article 250.2, and required in 250.4 (A)(5)
- Likewise, per Canadian Standards Association CSA C22.2 No. 0.4-M1982 (R2009), using Canadian Electrical Code Part I, section 10-500 as a guide.
- Providing over-voltage protection in accordance with the applicable requirements of ANSI C62.11
Blocking Cathodic Protection Current
Providing DC isolation of objectionable DC ground currents from cathodic protection systems as defined in NFPA 70, Article 250.6(E)
HAZARDOUS LOCATION USE
The PCR has been certified for use in Class I, Division 2, Groups A, B, C, D hazardous locations by UL, C-UL, according to:
- U.S. National Electrical Code sections 500-505
- ANSI/ISA 12.12.01
- CSA C22.2 No.213-M1987 (R2008)
The PCR has been certified to the ATEX Directive 94/9/EC for use in Zone 2, Group IIC hazardous locations by DEMKO, according to EN 50021.
Polarization cell: The polarization cell is an electrochemical switch comprised of pairs of stainless steel or nickel plates immersed in a solution of potassium hydroxide. It responds to DC current by polarizing the plates and reducing the flow of DC current. This occurs up to the threshold of about 1.2V, after which it effectively becomes a dead short. AC current can pass through the device. The electrolyte usually has an oil film on the top to prevent the evaporation. This electrolyte is a hazardous material, with issues of safety, disposal, and environmental concerns. Regular maintenance of the fluid level is needed, especially under conditions where high AC steady-state induced current is present, which can cause the fluid level to be reduced. Fluid level must be maintained to provide the nameplated AC fault current rating, otherwise the surface area for conduction is reduced. On some interval, the fluid is replaced with new electrolyte.
Dairyland PCR: The PCR is a solid-state device which provides DC isolation and AC grounding, up to a threshold of about 3V. It has low AC impedance, allowing induced AC current to be shunted to ground, while providing a high impedance to DC current flow. The solid-state design results in very consistent device characteristics. The device was introduced in 1994 and is used on a wide-spread basis as a replacement for polarization cells. An extensive user base has applied the PCR to pipeline systems, tanks, power cable casings, and separation of grounding systems, for AC grounding and DC isolation of cathodically protected structures. Applications include AC mitigation, lightning over-voltage protection, AC fault conduction, stray current blocking, and grounding electrical equipment that are tied to CP systems. On this last application, the PCR is the only UL listed device for providing an effective grounding path for electrical grounding as required per NEC section 250. Any PCR user is reference for DEI. There have been no reported failures of a PCR for any reason.
Specific comparison of polarization cells to Dairyland PCR
DC leakage current DC leakage current through the polarization cell is typically 1mA to about 40mA, while blocking 0.5V to 1.5V, respectively. This represents the amount of cathodic protection current that will be allowed to leave the pipeline through the device. Beyond about 1.2V, the polarization cell conducts heavily.
The PCR leakage current for the same voltage range as above is about 0.005mA to 0.5mA. It represents a reduction in leakage current to approximately 1/100th of that of a polarization cell, keeping the cathodic protection system current requirements minimized.
Lightning Surge Current Rating PCR: 100,000A crest (8x20 microsecond waveform) Polarization cell: no published value
AC Fault Current Ratings PCR: Various, stated at 1, 3, 10, 30 cycles for each rating Polarization cell: Various, 30 cycle rating
Blocking voltage: PCR: 3V Polarization cell: 1.2V typ. The polarization cell is sometimes arranged with two or more in series to achieve a higher blocking level. Our solid state approach never requires this.
Failure mode: PCR: Fail-safe; the device will always fail as a dead short Polarization cell: fails open
Neither device is a one-shot device. The PCR can see an unlimited number of operations within its rating. Any failure is non-eventful, and the unit can be easily factory repaired and returned. There have been no failures in the history of the product. The "fail-safe" approach is a significant safety issue, protecting workers and equipment.
Hazardous electrolytes: PCR: none Polarization cell: Potassium hydroxide
Maintenance requirements: PCR: none Polarization cell: regular fluid checks. Occasional fluid replacement. Eventual disposal of electrolyte.
The cost of maintenance over the life of the polarization cell, coupled with the cost of safety matters, liability, environmental damage, and decommissioning, has driven a significant number of past users of polarization cells to replace them with PCRs. This is evident at most major power utilities, and a vast number of gas and liquid pipeline systems. Many major consulting engineers now specify our solid-state devices for DC isolation and AC grounding.
Third party listing: PCR: UL and C-UL listed as an "effective grounding path," and can be installed in grounding conductors of electrical equipment. Also listed for hazardous locations: Class I, Division 2 Polarization cell: none There are actually no other known devices that are third party listed in this area.
Note: If all items are purchased together, Dairyland will factory assemble all components upon request.