CT and PT Polarity and Terminal Markings
Read current- and voltage-transformer polarity conventions, distinguish H/X and P/S labels, and identify manufacturer diagrams and secondary-circuit limits.
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Polarity and winding marks
Polarity marks identify a relationship used when interpreting transformer connections and instrument signals. They do not identify a safe-to-touch point or a complete meter wiring arrangement. Current transformers and voltage transformers have different secondary-circuit handling requirements.
| Marking context | What it identifies | What must be verified |
|---|---|---|
| H1 / H2 on a CT | The documented primary polarity/orientation reference | A window CT may mark a side of the opening rather than expose primary terminals. |
| X1 / X2 on a CT | The documented secondary terminal/polarity pair | The relationship to H1, the meter current input, and the exact wiring diagram. |
| P1 / P2 and S1 / S2 | Another primary/secondary marking convention | Use the actual manufacturer diagram; do not relabel an unknown device from appearance. |
| Dot / polarity mark | Corresponding instantaneous polarity references in the stated convention | Not a statement of RMS voltage, ratio, or permitted grounding point. |
| PT / VT | A potential/voltage transformer application | The nameplate, voltage ratio, fusing, secondary rating, and instrument wiring. |
| Ratio / burden / accuracy information | Separate ratings relevant to the measurement application | A correct ratio alone does not prove an adequate or correctly connected measurement system. |
CT reference path
The Schneider FAQ identifies the polarity-marked CT side in its stated application. A meter also needs the current channel associated with the correct voltage phase and a correctly interpreted direction. A polarity or phase-association error cannot be diagnosed only by a CT ratio calculation.
Never open a CT secondary while its primary is energized. Use the manufacturer’s documented shorting and isolation arrangements through the qualified work procedure; this drawing does not supply that procedure.
Voltage transformer convention
A voltage transformer’s primary and secondary polarity references describe corresponding winding relationships. They are not a direction to connect its secondary like a CT burden circuit. In particular, a voltage-transformer secondary must not be shorted as though it were a CT secondary.
Confirm ratio, rated voltage, polarity, fusing/protection, grounding arrangement, burden, and meter-channel connections from the manufacturer and project diagrams. Different instrument-transformer product families can use different terminal conventions.
Collect the exact diagrams
- Record the instrument-transformer catalog, ratio, polarity marks, orientation, and terminal identifiers.
- Obtain the transformer and instrument connection drawings for the actual configuration.
- Check phase association, secondary ratings/burden, protective and isolation arrangements, and applicable grounding requirements.
- Have unresolved markings or discrepancies reviewed before connection or testing.
The existing CT ratio and meter multiplier calculators perform separate numerical tasks. Record actual test evidence in the test record.