Inst ToolsInst ToolsInst Tools
  • Ask
  • Courses
  • Videos
  • Q & A
    • Interview
      • Instrumentation
      • Electronics
      • Electrical
      • Practical Questions
    • MCQ
      • Instrumentation MCQ
      • Electrical MCQ
      • Electronics MCQ
      • Control Systems MCQ
      • Analog Electronics MCQ
      • Digital Electronics MCQ
      • Power Electronics MCQ
      • Microprocessor MCQ
      • Multiple Choice Questions
  • EE
    • Electronics
      • Electronics Q & A
      • Electronic Basics
      • Electronic Devices & Circuits
      • Electronics Animation
      • Digital Electronics
    • Electrical
      • Electrical Basics
      • Electrical Q & A
      • Power Electronics
      • Electrical Machines
      • Electrical Animation
      • Power Systems
      • Switchgear & Protection
      • Transmission & Distribution
  • Measure
    • Control Valves
    • Calibration
    • Temperature
    • Pressure
    • Flow
    • Level
    • Analyzers
    • Switches
    • Vibration
    • Solenoid Valve
  • Control
    • PLC Tutorials
    • Control Systems
    • Safety Instrumented System (SIS)
    • Communication
    • Fire & Gas System
  • More
    • Design
    • Tools
    • Animation
    • Basics
    • Formulas
    • Standards
    • TextBooks
    • Common
    • Software
    • Excel Tools
    • Erection & Commissioning
    • Process Fundamentals
    • Videos
    • Books
Search
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Reading: What are Inverse Time and Instantaneous Trip Circuit Breakers?
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • PLC Tutorials
  • Control Systems
Search
  • Ask
  • Courses
  • Videos
  • Q & A
    • Interview
    • MCQ
  • EE
    • Electronics
    • Electrical
  • Measure
    • Control Valves
    • Calibration
    • Temperature
    • Pressure
    • Flow
    • Level
    • Analyzers
    • Switches
    • Vibration
    • Solenoid Valve
  • Control
    • PLC Tutorials
    • Control Systems
    • Safety Instrumented System (SIS)
    • Communication
    • Fire & Gas System
  • More
    • Design
    • Tools
    • Animation
    • Basics
    • Formulas
    • Standards
    • TextBooks
    • Common
    • Software
    • Excel Tools
    • Erection & Commissioning
    • Process Fundamentals
    • Videos
    • Books
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Electrical Basics > What are Inverse Time and Instantaneous Trip Circuit Breakers?

What are Inverse Time and Instantaneous Trip Circuit Breakers?

Learn the inverse time and instantaneous trip circuit breakers principle, operation, advantages, and disadvantages.

Last updated: September 28, 2022 2:36 pm
R Jagan Mohan Rao
Electrical Basics
No Comments
Share
4 Min Read
SHARE

Circuit breakers are available in two types.

Contents
Inverse Time Circuit BreakersInstantaneous Trip Circuit Breakers
  1. Inverse-time circuit breakers, also called Thermal-magnetic circuit breakers.
  2. Instantaneous circuit breakers are also known as magnetic-only circuit breakers.

Inverse Time Circuit Breakers

The inverse time circuit breakers associates with a thermal characteristic. At lower over current levels, the circuit breaker must wait for some time to see if this temporary fault.

After letting the overcurrent flow for some time, if it is still experiencing some fault current then the interrupting circuit breaker must break the circuit. This is called the inverse time characteristic.

Inverse Time Circuit Breaker

These breakers commonly use a bimetallic element that bends to hit a trip release when it is heated. With a low overcurrent, the heating is low and the element bends slowly. More overcurrent more heating and faster it bends. Hence, it is “inverse time”.

Inverse time circuit breakers have both thermal and instantaneous trip characteristics and are preset to trip at standard adjustable settings. Their characteristic inverse time-tripping under overload conditions is ideally suited for many applications ranging from residential to heavy industrial loads.  

The thermal action of the inverse circuit breaker responds to heat. If a motor’s ventilation inlets and outlets are not sufficient to removing heat from the windings of the motor, the heat will be detected by the thermal action of the circuit breaker.

In the case of a short circuit, the magnetic action of the circuit breaker will detect the instantaneous values of current and trip the circuit breaker.

The National Electrical Code (NEC 430.52) requires inverse time circuit breakers to be sized to a maximum of 250% of the motor full-load amperes (FLA).

Instantaneous Trip Circuit Breakers

The instantaneous breakers, also known as magnetic-only circuit breakers. They look like thermal-magnetic circuit breakers.

They don’t have a thermal trip function and will not protect from an overcurrent, not even for themselves.

Instantaneous Trip Circuit Breakers

They react only to instantaneous currents such as short circuits. Instantaneous-trip circuit breakers are designed for one very specific purpose, that being to provide branch-circuit short-circuit protection for motor circuits. As per the NEC standard, their use only in listed combination motor controllers.

The most widespread use of these breakers is in combination with motor starters. A motor starter comprises a contactor and overload relay.

The contactor has a different function and provides no protection for the motor, the motor’s circuit nor itself. The overload relay provides motor overload protection as well as cable overload protection so long as the cable is sized properly.

Reference: F. A. Scheda, “Transient inrush current in high-efficiency and standard motors”, IEEE Trans.

If you liked this article, then please subscribe to our YouTube Channel for Instrumentation, Electrical, PLC, and SCADA video tutorials.

You can also follow us on Facebook and Twitter to receive daily updates.

Read Next:

  • What is a Megger?
  • Types of Electrical Wiring
  • Motor Speed Control using VFD
  • AC Motor Speed Control
  • What is a Protective Relay?
Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !
Comparison of Electrical Protection Relays
Cathodic Protection – Sacrificial Anodic and Impressed Current
What is Variable Air Volume Controller in HVAC?
What is a Line Choke or Reactor in a VFD?
Electrical Terminology
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
208kSubscribersSubscribe
38kFollowersFollow

Categories

Recent Comments

  • Kamli on Top Free PLC Software
  • Guifty Shimica on Top Non-PLC Certification Courses for Automation Professionals
  • Guifty Shimica on Top Non-PLC Certification Courses for Automation Professionals
  • MIHARITSOA Aina Sitraka on Top Non-PLC Certification Courses for Automation Professionals

Related Articles

What is a Magnetic Field

Difference Between Electric Field and Magnetic Field

Why Circuit Breakers Don't Protect People?

Why Circuit Breakers Don’t Protect People?

Types of Motor Enclosures

Types of Motor Enclosures

Electrical Maintenance Engineer's Biggest Enemy

Electrical Components Overheating – Causes, Troubles, Prevent

Burst Transformers Root Cause Analysis

Root Cause Analysis – Burst Transformers and 11 kV Input Breakers

4-20mA VFD Drive Formula

4-20mA Linear Conversion Calculation for VFD Drive (Formula)

VFD Pros and Cons - Variable Frequency Drives

VFD Pros and Cons – Variable Frequency Drives

Induction Motor Operation

Induction Motor Over and Under Voltage Problems

More Articles

Safety Relief Valve

Safety Relief Valve Quiz: Test Your Knowledge

How to Update the Firmware Version of your PLC

How to Update the Firmware Version of your PLC? – TIA Portal

Swiss Screw Machining

Things You Should Know About Swiss Screw Machining

Instrument Maintenance and Calibration System

Instrument Maintenance and Calibration System

Schottky Diode Vs PN junction Diode

Difference between Schottky Diode and PN junction Diode

Power Electronics Objective Questions

Power Electronics Diode Circuits Questions and Answers

Process Control Instrumentation Objective Questions

Process Control Instrumentation Quiz

Solenoid Valves Questions

Solenoid Valves Questions & Answers – 3

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?