# Combined instrument transformer

Canonical URL: https://eloragrid.ai/symbols/combined-instrument-transformer
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: CT/VT
Drawing use: SLD, Schematic
Reference families: IEC, Manufacturer

Single unit housing a current transformer and voltage transformer for each phase, typical of MV and HV metering points.

## In plain English

### What does Combined instrument transformer mean?

A combined instrument transformer places a CT and a VT in one insulated housing for each phase. It saves space and foundations at outdoor higher-voltage metering points and appears in MV metering units where the supply authority needs both current and voltage for a billing meter.

### A simple example

On a single-line diagram the CT and VT symbols are drawn together with a boundary showing they share one housing. The boundary does not change ratios or classes, which are still stated separately for the current and voltage parts.

### What the drawings help you do

Read the CT and VT ratings separately. Check sealing and access requirements for revenue metering. A combined instrument transformer houses a CT and VT together; separate units are drawn and specified independently.

### This particular reference

Single unit housing a current transformer and voltage transformer for each phase, typical of MV and higher-voltage metering points. A combined instrument transformer houses a CT and VT together; separate units are drawn and specified independently.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Phase: One of the related AC waveforms in a power system.
- Rating: A value stating the conditions for which equipment is specified.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers)
- [CPB capacitor voltage transformer](https://www.hitachienergy.com/uk-ie/en/products-and-solutions/instrument-transformers/voltage-transformers/cpb-72-800-kv)


## What it represents

A combined instrument transformer places a CT and a VT in one insulated housing for each phase. It saves space and foundations at outdoor HV metering points and appears in MV metering units where the supply authority needs both current and voltage for a billing meter.
On a single-line diagram the CT and VT symbols are drawn together with a boundary showing they share one housing. The boundary does not change ratios or classes, which are still stated separately for the current and voltage parts.

## How to read it

- Read the CT and VT ratings separately.
- Check sealing and access requirements for revenue metering.

## Information to show or reference

- State CT ratio and class
- State VT ratio and class
- Show sealing or metering boundary

## Important distinction

A combined instrument transformer houses a CT and VT together; separate units are drawn and specified independently.

## Facts

- Contents: CT and VT in one housing
- Typical use: Revenue metering points
- Preview: Independent educational concept; consult the applicable standard and project legend for the exact graphic

## 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 manufacturer overview of indoor current and voltage instrument transformers.
- [CPB capacitor voltage transformer](https://www.hitachienergy.com/uk-ie/en/products-and-solutions/instrument-transformers/voltage-transformers/cpb-72-800-kv) — Hitachi Energy. Public instrument transformer product family context.

## 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.