Protective relay symbol
Also called Relay, IED, Protection relay
A protective relay measures current and voltage from the CTs and VTs and trips the breaker when it sees a fault. On ANSI drawings each function is named by its device number, such as 51 for time overcurrent.
What the protective relay symbol means
A protective relay measures current and voltage from the CTs and VTs and trips the breaker when it sees a fault. On ANSI drawings each function is named by its device number, such as 51 for time overcurrent.
ANSI and IEC symbols
A circle with the ANSI device number of each function, for example 50/51 or 87T. See ANSI device numbers.
ANSI SVGWhere you see it
On every protected breaker, transformer, generator, motor and busbar.
What is written next to it
On a one-line, the protective relay carries its tag and its ratings: the device functions, the CT and VT inputs and the breakers it trips.
What gets checked at commissioning
Before the protective relay is energised, the test records usually cover: secondary injection of each function against the relay settings, trip checks through to the breaker and communications. Each check is recorded against the tag, so the system can be handed over with its evidence. See commissioning software.
ANSI device numbers
Protective functions you will often find with a protective relay:
- 50/51 overcurrent
- 87 differential
- 86 lockout
See the full list of ANSI device numbers with their IEC equivalents.
Related symbols
Frequently asked questions
What does the protective relay symbol look like?
On ANSI drawings: A circle with the ANSI device number of each function, for example 50/51 or 87T. See ANSI device numbers. In IEC 60617: A box with the quantity and its limit inside: I> for overcurrent, U< for undervoltage, Id> for differential.
Is the protective relay symbol the same in IEC and ANSI?
No. A box with the quantity and its limit inside: I> for overcurrent, U< for undervoltage, Id> for differential. The IEC 60617 number is S00327.
Where is a protective relay used?
On every protected breaker, transformer, generator, motor and busbar.
Which ANSI device numbers go with a protective relay?
50/51 overcurrent, 87 differential, 86 lockout.
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