Current Transformer (CT) Metering (Single-Phase & Three-Phase)
Services greater than 400 amp (320amps continuous current) require CT metering. This type of metering system requires prior approval from a Skamania County PUD Representative and requires an additional construction charge. This service requires a different meter base and equipment.
Skamania PUD installs the CT’s, meter and associated wiring. The customer provides and installs any additional metering equipment beyond the service entrance. PUD approval is required for the location of the CT metering equipment.
Current Transformer (CT) metering is required in the following scenarios:
- Three phase service exceeding 400 amp.
-
Single Phase service exceeding 400 amps (320 amp continuous).
- CT Metering at either a pad-mount transformer or on a pole shall have no more than two (2) services fed from it.
CT Metering equipment shall meet the following requirements:
- Securely mounted, plumb and level on the outside of the structure.
- Rain tight and NEMA 3R-Rated.
- 6 feet maximum height to top of CT cabinet or center of meter socket.
- Grounding and bonding of both the meter base and CT enclosure in accordance with the NEC and local governing office.
- Bottom of CT cabinet is a minimum of 18 inches above final grade.
- Side opening, hinged door with sealing provisions.
- Factory-installed hinges located on the opposite side of the enclosure from there the meter socket is located.
- Will not be used as a junction box or bus gutter.
CT Metering Conduit
CT Metering conduit between the CT enclosure and the meter base shall meet the following requirements:
- 1-inch minimum electrical conduit for single-phase service and 1 ¼-inch minimum for three-phase services.
- Schedule 40 PVC or rigid galvanized conduit.
- Grounding bushings at both ends of if galvanized conduit is used.
- A continuous run, with no conduit bodies (LB joints, condulets, etc.).
- Conduit installed with no more than (3) 90-degree elbows in the total length (270 degrees total).
- Conduit entering the meter enclosure adjacent to the test switch.
-
CT Enclosure mounting base specifications:
- 401-800amp Single-Phase 30”W x 36”H x 11”D
- 401-800amp Three-Phase 36”W x 48”H x 11”D
CT Mounting Base
Installation requirement for current transformer mounting bases are as follows:
- Mounting base is rated for a minimum of 50k amps fault current.
- Line and load side terminations require two bolts per connector and two bolts on the neutral bus.
- Customer furnishes all lugs and terminates both load and line side conductors to the bus.
- A 4-wire delta service requires orange marking of the high leg.
Switchboard Metering
Switchboard metering is required for three-phase services over 800amps. At the customer’s option, this type of metering may be installed for services sized 201-800amp. The customer-installed equipment must be EUSERC-approved.
All customer-installed switchboards require:
- Current Transformer (CT) mounting base.
- Service section.
- Set of bars/links.
- Panel(s).
- Meter base with provisions for a test switch.
- Means for locking the meter enclosure with independent 24-hour access to utility personnel.
- Case ground as required per the NEC.
Note: Customers requiring more than 480 volts of service will have primary metering. Ownership and maintenance agreements for primary metered services will be mutually agreed upon with Skamania PUD.
Grounding & Bonding Requirements
Grounding and bonding is critical for safety and electrical reliability. The customer is responsible to ensure that the electrical wiring and service equipment is grounded and bonded in accordance with the NEC and the local governing office.