Test Switch Operation, Specification & Accessories

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10/02/2012 Slide 1 Test Switch Operation, Specification & Accessories Notes from the Field Prepared by Tom Lawton,TESCO for the NC Electric Meter School 2013

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An Introduction to Test Switches. Presented at the North Carolina Electric Meter School. 6/2013

Transcript of Test Switch Operation, Specification & Accessories

  • 1. 10/02/2012 Slide 1Test Switch Operation,Specification &AccessoriesNotes from the FieldPrepared by Tom Lawton,TESCOfor the NC Electric Meter School 2013

2. Agenda Introduction Using Test Switches Meter Test Switch Specifications Meter Test Switch Configurations Meter Test Switch Accessories Pre-Wired Transformer Rated Enclosures 3. Typical Self Contained Service Typically found inresidential metering Meters are capable ofhandling the directincoming amperage Meter is connected directlyto the load being measured Meter is part of the circuit When the meter isremoved from the socket,power to the customer isinterrupted 4. Transformer Rated Service Meter measures scaleddown representation of theload. Scaling is accomplished bythe use of external currenttransformers (CTs) andsometimes voltagetransformers or PTs). The meter is NOT part of thecircuit When the meter is removedfrom the socket, power tothe customer is not effected. 5. Test Switch SafetyTesting current transformers while they are in service can be a dangerousoperation if certain safety procedures are not followed. The secondary loop of acurrent transformer must NEVER BE OPENED when service current is present inthe primary. When there is current in the primary, and the secondary of a currenttransformer is open circuited, the voltage across the secondary can rise tohundreds and even thousands of volts, creating an extremely dangeroussituation. The open CT secondary voltage magnitude varies with CT design andprimary current flow. The high voltage that is present on the open secondary ofan energized current transformer generates two great hazards. The first hazard isELECTRICAL SHOCK TO TESTING PERSONNEL. The second hazard is THEBREAKDOWN OF THE CURRENT TRANSFORMER INSULATION. Both hazardscan be avoided provided that the secondary of the current transformer is neveropened. The safest current transformer installations for testing are those thathave a Test Switch as part of the secondary loop. A Test Switch is a device thatwill facilitate inserting instrumentation in the current transformer secondary loopwithout the danger of opening the circuit. 6. Meter Test Switch Specifications ANSI C12 Definitions Test Switch Materials Plating Barriers Wiring Connections What to look for Covers 7. ANSI C12.9 Test Switch DefinitionsFor Test Switches and Jacks for Transformer-Rated Meters1 ScopeThis standard is intended to encompass the dimensions and functions of meter test switchesused with transformer-rated watthour meters in conjunction with instrument transformers and testplugs used in conjunction with the test switch.2 Definitions2.1 short-circuiting switchA single-pole double-throw (make-before-break) transfer switch used to transfer currentaway from the meter.2.2 test jackA spring-jaw receptacle in the current element of a test switch that provides a bipolar testconnection in the metering current circuit without interruption of the current circuit.2.3 test jack switchA single-pole single-throw disconnect switch used in conjunction with a test jack toprovide a parallel current path during normal operating conditions.2.4 test plugA bipolar mating plug to a test jack for inserting instrumentation into the metering currentcircuit.2.5 voltage switchA single-pole single-throw switch used to open or close a voltage circuit.3 Standard ratings3.1 CurrentThe current rating shall be 20 A minimum.3.2 VoltageThe voltage rating shall be 300 V or 600 V.4 General requirements for test switches4.1 Material and workmanshipThe test switch and its components shall be substantially constructed of suitable material in aworkmanlike manner.4.2 NameplatesNameplates are not required on these test switches, but a manufacturers identifying marking(such as catalog number, trademark, etc.) shall be stamped, printed, affixed, or cast in aconvenient place on each test switch. When required, a warning label indicating hidden internaljumpers should be affixed.4.3 Movable partsMovable conducting parts such as blade hinges shall be held in place by locknuts or pins or theirequivalent, arranged so that a firm and secure connection will be maintained at any position ofthe switch blade.AMERICAN NATIONAL STANDARD ANSI C12.9-2011 8. ANSI C12.9 Test Switches 9. ANSI C12.9 Test Switches 10. ANSI C12.9 General Test Switch Specifications 11. Meter Test Switch Configurations Layout Handle Colors Reversed vs.Normal Potentials Current Links Base Sizing Barrier Locations 12. Meter Test Switch Accessories Test Plugs Safety Covers Test Switch IsolatorsNOTE: On installations that contain TestSwitches, test leads terminated with a testswitch safety test probe (test plug) shouldbe used for CT testing. This provides amake-before-break connection to preventaccidental opening of the currenttransformer secondary loop. 13. ANSI C12.9 Test Jack Specifications 14. ANSI C12.9 Test Plug Specifications 15. Pre-Wired Transformer Rated Enclosures Cover Types Wiring Sockets 16. Questions and DiscussionTom LawtonTESCO The Eastern Specialty CompanyBristol, PA1-800-762-8211This presentation can also be found under MeterConferences and Schools on the TESCO web site:www.tesco-advent.com