Single Phase Three Wire Electrical Service

Current transformers (CTs) measure the amount of electric current flowing in a conductor. A WattNode® meter, which also measures voltage, uses current and voltage measurements to calculate power and energy (kW and kWh).

CCS only sells “safe”, low-voltage outputs CTs. This type of CT is calibrated to output exactly 0.333 volt when the current flowing in the CT’s primary (opening) is equal to the CT’s full-scale current rating.

To select a CT, we recommend first deciding on a style, either an opening (split-core) or a solid-core CT, then select the model you need based on the maximum load current you are measuring and the size of the conductor being monitored.

CAUTION! WattNode meters can only be used with 0.333 volt output CTs. Other types of CTs can generate lethal high voltages that can permanently damage equipment.

CT Styles

  • Split Core CTs (opening) have a removable section, so that they can be installed without interrupting the circuit, and they are available in three opening sizes.
  • Solid Core CTs (toroidal) are more compact and accurate. You must disconnect the measured circuit to install solid core CTs, so they are better suited for new wiring or permanent installation.
  • Bus Bar CTs are also split core CTs, but are available in larger sizes and higher current ratings. They have a removable section, so that they can be installed without interrupting the circuit.

CT Opening Sizes

CTs are sized to fit around the conductor being measured. Rectangular split core opening sizes include 0.35, 0.75″, 1.25″, and 2.0″. Solid core CTs are available with openings from 0.3″ to 1.25″. Bus bar styles are available in virtually any opening size from 1″ x 2.5″ up to 8″ x 24″.

CT Current Ranges

Standard CTs are available with full scale rated currents from 5 amps to 3000 amps. CTRC Rogowski coils and custom bus bar CTs are available with full scale current ratings up to 6000A.

See Also

Keywords: current transformer, split core CT, toroidal core, opening CT, bus bar