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
Symbols · TS
Potential test switch
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.
- 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.
Read the source: Transformer terminals for measuring and test circuits · IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
Schematic · TS
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
A distinction that matters
A potential test switch opens a voltage circuit; a current test switch shorts the CT before opening.
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.
IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
IEEE graphic-symbol standards context; no standard glyph is reproduced.
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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