# Test plug

Canonical URL: https://eloragrid.ai/symbols/test-plug
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: TP
Drawing use: Schematic
Reference families: Manufacturer

Plug inserted into a test block or switch to connect test equipment to the relay side while isolating the plant side.

## In plain English

### What does Test plug mean?

A test plug fits into a test block or test switch and brings each pole out to test leads. Depending on its design it can connect test equipment to the relay side only, or link plant and relay sides through an ammeter for in-service current measurement.

### A simple example

Different plug types for the same block do different things, so the procedure must name the plug variant. The symbol shows the plug's poles but not its internal links, and using the wrong plug can open a live CT circuit or leave a trip output connected.

### What the drawings help you do

Check which plug variant the procedure requires. Read the internal links of each pole. A test plug is the removable part; the test block or switch is the fixed part wired into the circuit.

### This particular reference

Plug inserted into a test block or switch to connect test equipment to the relay side while isolating the plant side. A test plug is the removable part; the test block or switch is the fixed part wired into the circuit.

### Terms

- 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.
- 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.

- [Transformer terminals for measuring and test circuits](https://www.phoenixcontact.com/en-ie/products/terminal-blocks/transformer-terminal-blocks?p=7)


## What it represents

A test plug fits into a test block or test switch and brings each pole out to test leads. Depending on its design it can connect test equipment to the relay side only, or link plant and relay sides through an ammeter for in-service current measurement.
Different plug types for the same block do different things, so the procedure must name the plug variant. The symbol shows the plug's poles but not its internal links, and using the wrong plug can open a live CT circuit or leave a trip output connected.

## How to read it

- Check which plug variant the procedure requires.
- Read the internal links of each pole.

## Information to show or reference

- Name plug variant
- Show internal links
- Match pole numbers to the block

## Important distinction

A test plug is the removable part; the test block or switch is the fixed part wired into the circuit.

## Facts

- Function: Connects test equipment through a test block
- Variants: Isolating and in-service measuring types
- 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.

## 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.