CT
Multi-core current transformer
CT with several independent magnetic cores on one primary, each with its own secondary for metering or protection.
SLD / Schematic
Symbols · BCT
Bushing current transformer
Toroidal CT mounted around a transformer or breaker bushing, often with a tapped multi-ratio secondary.
In plain English
What does Bushing current transformer mean?
A bushing CT is a toroidal core and secondary slipped over the bushing of a power transformer, generator or dead-tank circuit breaker. The bushing conductor is the primary, and several CTs may be stacked on one bushing for differential, overcurrent and metering duties.
A simple example
Bushing CTs are often multi-ratio, with taps on the secondary, and only the selected tap should be wired to the relay. The symbol shows the location at the bushing, so the reader must check which side of the breaker or transformer the CT sits on to understand the protection zone overlap.
What the drawings help you do
Identify which side of the device each bushing CT sits on. Check the selected tap on multi-ratio CTs. A bushing CT uses the bushing conductor as its primary; a free-standing CT has its own insulated primary.
This particular reference
Toroidal CT mounted around a transformer or breaker bushing, often with a tapped multi-ratio secondary. A bushing CT uses the bushing conductor as its primary; a free-standing CT has its own insulated primary.
- Winding
- A coil of conductor inside an electrical machine or transformer.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Terminal
- An identified point where a conductor connects.
Read the source: Indoor current and voltage transformers · IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
SLD / Schematic · BCT
What it represents
A bushing CT is a toroidal core and secondary slipped over the bushing of a power transformer, generator or dead-tank circuit breaker. The bushing conductor is the primary, and several CTs may be stacked on one bushing for differential, overcurrent and metering duties.
Bushing CTs are often multi-ratio, with taps on the secondary, and only the selected tap should be wired to the relay. The symbol shows the location at the bushing, so the reader must check which side of the breaker or transformer the CT sits on to understand the protection zone overlap.
How to read it
- Identify which side of the device each bushing CT sits on.
- Check the selected tap on multi-ratio CTs.
Information to show or reference
- State selected tap and full ratio
- Show position relative to the breaker or winding
- Mark polarity
A distinction that matters
A bushing CT uses the bushing conductor as its primary; a free-standing CT has its own insulated primary.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Indoor current and voltage transformers
Public manufacturer overview of indoor current and voltage instrument transformers.
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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