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  • CT – Current transformer – CTs measure the AC (sometimes DC) current in a wire by transforming the current to a lower current or voltage. CCS CTs are voltage output, generally 0.333 Vac at full-scale, eliminating any shock hazard.
  • Three-phase – Refers to electrical services where there are three AC line conductors with AC voltage waveforms 120° out-of-phase from each other. This is commonly found in commercial and industrial settings; almost never in residential wiring.
  • Single-phase – Refers to an electrical service with only a single AC voltage phase. In residential settings, this is commonly 120/240 Vac. Although the two line voltages in residential services are 180° out-of-phase from each other, it is not called two-phase, since both line voltages are derived from a single-phase of the utility medium voltage distribution transformer.
  • Three-wire – This term is a bit ambiguous. It may refer to a three-wire residential service with L1, L2, and neutral. Or it may refer to three-wire three-phase service, in which case it indicates service without a neutral conductor.
  • Four-wire – Generally this refers to three-phase service with a neutral wire.
  • Delta – This refers to a type of distribution transformer wiring where the windings are connected in a triangle (delta) arrangement: A-B, B-C, C-A. This is commonly associated with three-wire service, but not always: there are four-wire delta services.
  • Wye – This refers to a type of distribution transformer winding where each winding is connected to neutral in a “Y” arrangement: A-N, B-N, C-N. This may be used to derive four-wire or three-wire circuits (just leave the neutral unconnected).
  • One-line diagram – A one-line electrical diagram or single-line diagram (SLD) is a common graphic convention use in electrical plans to represent a three-phase power system by drawing only one of the phases.
  • TI – Technical Information – usually refers to the electrical wiring drawings. Sometimes also called “TI drawings”.

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