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Electric Service Handbook

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Pages: Current and Voltage Transformer Metering

Current and Voltage Transfomer Metering Requirements

General Requirements
  • Single-phase services over 400 amps (320 amps of load) require transformer rated metering.
  • Three-phase services over 200 amps require transformer rated metering.
  • Single-phase & three-phase services with voltages greater then 240 volts require transformer rated metering. (see exception below)
  • The current transformers and voltage transformers, when required, will be provided by DEA and installed by the Member.
  • The CT and VT wiring between the meter socket and the CT's and VT’s will be provided and installed by DEA personnel.
  • The current transformers and voltage transformers shall be installed ahead of the Member’s service disconnect.
  • Meter socket meeting Dakota Electric requirements, provided and installed by Member.
  • Metering Transformer Cabinet shall be provided and installed by Member.
  • Wire distance between Meter socket and CT's/VT's is no more then 50 ft. (recommended to keep this distance shorter, typically less then 25 ft)
 
Conduit and Wire Size
  • All current transformer and voltage transformer wiring shall be provided and installed by DEA.
  • For all services, the conduit from the CT cabinet to the meter is to be at least 1 inch in diameter. This conduit is provided and installed by the Member or Member’s contractor.
  • The wire is #12 stranded or larger and the insulation to be T.H.H.N. This wire is provided and installed by Dakota Electric.
  • The maximum distance between the current transformers and the meter shall not be longer than 50 feet and it is recommended to keep this distance shorter, typically less then 25 feet.
No Member wiring (other than the service conductors) shall be installed in the current transformer cabinet, meter socket, or conduits dedicated for metering wires. Also, to ensure metering accuracy, no Member wiring shall be permitted to be connected to the Association’s metering secondary wiring.
 
Metering Transformer Cabinet - The Member is required to supply a UL (Underwriters Laboratories) or ARL (Applied Research Laboratories) approved cabinet for the current transformers and voltage transformers, if transformer rated metering is required for the service.
  • Transformer cabinets mounted outside shall be approved for that purpose.
  • DEA distribution transformers shall not be used for metering:
    • No current transformers or voltage transformers shall be mounted within the DEA distribution transformer.
    • No holes shall be drilled or cut into the side of a DEA distribution transformer cabinet.
    • No metering sockets or metering transformer cabinets shall be mounted on the DEA distribution transformer.
  • All metering transformer cabinets shall have hinged doors and latching mechanisms whereby DEA can install a padlock.
  • The transformer cabinet shall have provisions for grounding and for mounting current transformers.
Exception to Voltage Transformer (VT) requirement on 480V metering - Self-contained metering may be used if all of the following requirements are met:
  • The service is 200 amps or less.
  • The metering is cold sequenced. Cold sequenced means a full load interrupting rated disconnect switch capable of being locked in the open and closed position, mounted ahead of the metering, this switch is used to de-energize the service along with the metering for working on the metering.
  • The service can be routinely and easily shut off during Dakota Electric's normal business hours and during non-business hours as required. 480V services that are not eaisly denergized during normal business hours, will not be allowed to be installed as self-contained metering. A service to an irrigation pump is a good example of a service which can be easily shut off during the Dakota Electric's normal business hours.
  • This exception must be approved by Dakota Electric and by installing a cold sequenced meter, the member agrees to allow Dakota Electric the ability to de-energize the service by using the disconnect, without notice, at any time. With this installation choice the member shall release Dakota Electric from any liability for operating this disconnect to denergize the electrical service.