CT test
CT test terminal
A current-transformer terminal arrangement providing documented test and shorting facilities.
Schematic
Symbols · TB
Relay test block
Multi-pole test facility between CT, VT and trip wiring and a relay, allowing safe isolation and test injection.
In plain English
What does Relay test block mean?
A relay test block sits in the secondary wiring between CTs, VTs, trip outputs and a protection relay. Inserting a test plug or opening the block isolates the relay from the plant, automatically shorts CT circuits before they are opened and isolates trip outputs, so the relay can be tested with secondary injection while the primary circuit stays in service.
A simple example
The schematic should show the order in which poles break and make, because CT shorting must occur before CT circuits open. The symbol alone does not show that sequence, so the terminal arrangement of each pole needs to be drawn or referenced to the manufacturer data.
What the drawings help you do
Check CT poles short before they open. Confirm trip outputs are isolated when the block is opened. A relay test block isolates and shorts circuits in one operation; a single CT test terminal handles only one conductor.
This particular reference
Multi-pole test facility between CT, VT and trip wiring and a relay, allowing safe isolation and test injection. A relay test block isolates and shorts circuits in one operation; a single CT test terminal handles only one conductor.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Terminal
- An identified point where a conductor connects.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: Transformer terminals for measuring and test circuits · Disconnect and knife-disconnect terminal blocks
Schematic · TB
What it represents
A relay test block sits in the secondary wiring between CTs, VTs, trip outputs and a protection relay. Inserting a test plug or opening the block isolates the relay from the plant, automatically shorts CT circuits before they are opened and isolates trip outputs, so the relay can be tested with secondary injection while the primary circuit stays in service.
The schematic should show the order in which poles break and make, because CT shorting must occur before CT circuits open. The symbol alone does not show that sequence, so the terminal arrangement of each pole needs to be drawn or referenced to the manufacturer data.
How to read it
- Check CT poles short before they open.
- Confirm trip outputs are isolated when the block is opened.
Information to show or reference
- Number each pole
- Show CT shorting arrangement
- Show trip isolation poles
A distinction that matters
A relay test block isolates and shorts circuits in one operation; a single CT test terminal handles only one conductor.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Transformer terminals for measuring and test circuits
Public manufacturer range of transformer and test terminals for measuring and protection circuits.
Disconnect and knife-disconnect terminal blocks
Public disconnect and test terminal families used in secondary circuits.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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Test plug
Plug inserted into a test block or switch to connect test equipment to the relay side while isolating the plant side.
Schematic
TS
Current test switch with shorting contact
Panel test switch for CT circuits that shorts the CT side before opening the relay side, with a test jack between.
Schematic
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