# CT multi-ratio tap selection reference

Canonical URL: https://eloragrid.ai/symbols/ct-multi-ratio-tap-selection-reference
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: CMTSR
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: CT tap connections
Output: Assigned current ratio

Identifies which documented secondary tap is used for the selected CT measurement ratio.

## In plain English

### What this block does

Identifies which documented secondary tap is used for the selected CT measurement ratio.

### A simple example

In a substation protection panel, separate CT cores can supply metering and protection circuits with different duties. A test boundary must preserve the secondary arrangement required by the selected CT and test device. For this reference, the drawing identifies “CT tap connections” at the input and “Assigned current ratio” at the output. Unconnected taps require the manufacturer's arrangement.

### What the drawings help you do

Start at the named input: CT tap connections. Identify its source device or document and the state represented on the drawing. Follow the named output: Assigned current ratio. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: CT tap connections
- Output: Assigned current ratio
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: CT tap connections → CMTSR → Assigned current ratio
A reading guide. The entry's original illustration and input/output facts describe this application.

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers)


## What it represents

Identifies which documented secondary tap is used for the selected CT measurement ratio. A current-transformer secondary arrangement carries a measuring current from a defined primary location to metering or protection inputs. Core identity, polarity and the connected circuit determine the measurement's meaning.
In a substation protection panel, separate CT cores can supply metering and protection circuits with different duties. A test boundary must preserve the secondary arrangement required by the selected CT and test device. For this reference, the drawing identifies “CT tap connections” at the input and “Assigned current ratio” at the output. Unconnected taps require the manufacturer's arrangement.
Trace every secondary connection and the assigned earthing point against the actual connection diagram. These illustrations explain circuit roles and never prescribe a live CT switching or disconnection procedure. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.

## How to read it

- Start at the named input: CT tap connections. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Assigned current ratio. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Unconnected taps require the manufacturer's arrangement.
- Trace every secondary connection and the assigned earthing point against the actual connection diagram. These illustrations explain circuit roles and never prescribe a live CT switching or disconnection procedure.

## Information to show or reference

- Label the source and connection reference for ct tap connections.
- Identify the destination and defined state of assigned current ratio.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Unconnected taps require the manufacturer's arrangement.

## Important distinction

Unconnected taps require the manufacturer's arrangement. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.

## Facts

- Representation: Functional block
- Installation focus: Substations
- Input / boundary: CT tap connections
- Output / connection: Assigned current ratio
- Lookup label: CMTSR is a library lookup label, not a standard device designation.

## Public references

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers) — ABB. Public technical context for current-transformer secondary arrangements. Current and voltage measurement transformers and their secondary interfaces. The application text and educational graphic are independently authored; the publisher does not certify this representation.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.