Video: Current Transformer (CT), Potential Transformer (PT) wiring standards

Search FAQs

Issue
What is the industry standard for current transformers (CTs) and potential transformers (PTs)? What is representation of letters H, X and S?

Product Line
3090 SCCT, UL2808 5 A Split-Core Current Transformers (CTs), and potential transformers (PTs)

Cause
Installation of CTs and PTs.

Environment
Installation and wiring of CTs and PTs

*Warning: Installation and maintenance of this device should only be performed by qualified, competent personnel that have appropriate training and experience with high voltage and current devices. Failure to follow the instructions / warnings in the Meter Installation Guide can result in permanent damage to the meter, severe injury or death.

Resolution
The industry standard for current transformers (CTs) are as follows:
The Primary or Line(source) side is designated with the letter 'H', "H1", or a white dot on the flat surface of the CT. Some CT's may have an arrow that points out the current flow direction from the source to the load.

The Secondary or Load side is designated with either the letter 'X' or 'S'.

X1 (White for 3090SCCTs) is the positive wire.
X2 (Black for 3090SCCTs) is the negative wire.

Schneider Electric model 3090SCCT or "UL2808 5 A Split-Core" current transformers identify the X1 (Positive) wire as WHITE and the X2 (Negative) wire as BLACK.

The industry standard for (PTs) are as follows:

The H1 is the primary positive terminal. This terminal may have a white dot on the casing to indicate polarity.
The H2 is the primary negative terminal.
The X1(S1) is the secondary positive terminal. This terminal may have a white dot on the casing to indicate polarity.
The X2(S2 is the secondary negative terminal.

Note: Always refer to the CT or PT cut sheet to verify color designation and detailed designations.

The following video discusses differences between control transformers and potential transformers: