# Potential test switch

Canonical URL: https://eloragrid.ai/symbols/potential-test-switch
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: TS
Drawing use: Schematic
Reference families: IEEE / ANSI, Manufacturer

Panel test switch that opens a VT secondary circuit to a relay or meter so test voltages can be applied safely.

## In plain English

### What does Potential test switch mean?

A potential test switch is a knife switch in a VT secondary circuit that isolates a relay or meter from the VT so test voltages can be injected. Unlike a current switch it has no shorting contact, because a VT secondary must never be shorted.

### A simple example

When the switch is open, protection that relies on the voltage may be disabled or may see loss of voltage. The symbol does not show that consequence, so the test procedure should list the functions affected and whether any trip outputs must also be isolated.

### What the drawings help you do

Confirm there is no shorting contact on VT circuits. List functions affected when the switch is open. A potential test switch opens a voltage circuit; a current test switch shorts the CT before opening.

### This particular reference

Panel test switch that opens a VT secondary circuit to a relay or meter so test voltages can be applied safely. A potential test switch opens a voltage circuit; a current test switch shorts the CT before opening.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Coil: A wound conductor that can produce a magnetic field when energised.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.

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.

- [Transformer terminals for measuring and test circuits](https://www.phoenixcontact.com/en-ie/products/terminal-blocks/transformer-terminal-blocks?p=7)
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/)


## What it represents

A potential test switch is a knife switch in a VT secondary circuit that isolates a relay or meter from the VT so test voltages can be injected. Unlike a current switch it has no shorting contact, because a VT secondary must never be shorted.
When the switch is open, protection that relies on the voltage may be disabled or may see loss of voltage. The symbol does not show that consequence, so the test procedure should list the functions affected and whether any trip outputs must also be isolated.

## How to read it

- Confirm there is no shorting contact on VT circuits.
- List functions affected when the switch is open.

## Information to show or reference

- Identify VT and relay sides
- Show associated trip isolation
- Reference test procedure

## Important distinction

A potential test switch opens a voltage circuit; a current test switch shorts the CT before opening.

## Facts

- Circuit: VT secondary
- Shorting contact: None
- Preview: Functional illustration of the device role; not a product footprint or certified standard graphic

## Public references

- [Transformer terminals for measuring and test circuits](https://www.phoenixcontact.com/en-ie/products/terminal-blocks/transformer-terminal-blocks?p=7) — Phoenix Contact. Public manufacturer range of transformer and test terminals for measuring and protection circuits.
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. IEEE graphic-symbol standards context; no standard glyph is reproduced.

## 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.