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What is Trip Class? Trip Class 5, 10, 10A, 20, 30, 40 Explained

What is trip class.

Overload relays are rated by a trip class that defines the length of time it will take for the overload relay to trip in an overload condition. The most common trip classes are Class 10, Class 20, and Class 30. In Europe, tripping curves of overload relays are defined by IEC Standard. In North America, the NEMA Standard defines trip classes.

IEC components are typically application-rated. This means the controller is sized very close to its operational limit for a given application. IEC motors are also generally more application-rated. For these reasons, the Class 10 trip is most common on IEC applications. Because NEMA products are applied with more built-in excess capacity, the Class 20 trip is the most common.

Trip classes according to NEMA

NEMA Standard MG-1 defines 4 types of Classes. The most common classes are 5, 10, 20 & 30.

Class 5, 10, 20 & 30 overload relays will trip within 5, 10, 20 & 30 seconds respectively at 600% of motor full load amps.

A Class 10 overload relay, for example, has to trip the motor offline in 10 seconds or less at 600% of the full load amps (which is usually sufficient time for the motor to reach full speed). Many industrial loads, particularly high inertia loads, require Class 30.

Class 5 is usually used for motors requiring fast tripping.

Class 10 is commonly used to protect artificially cooled motors such as submersible pump motors of low thermal capacity.

Class 20 is usually sufficient for general-purpose applications.

Class 30 is usually required for high inertial loads to help prevent nuisance tripping.

Trip classes according to IEC

A classification of the starting typology is linked to the characteristics required by the load and by the consequent behavior of the thermal relay. Compensated thermal relays have an operating principle for which their behavior remains unchanged when the working temperature varies.

The standard establishes the tripping times corresponding to 7.2 x Ir (Ir setting current of the thermal protection), based on which the concept of trip class or starting class is introduced, as shown below.

The meaning of the different terms in this table can be better explained by referring to the following considerations.

The parameter 7.2 x Ir is the multiple of the current set on the protection relay and the multiplying factor 7.2 is fixed by the product standard.

“Ir” usually coincides with the rated current of the motor “Ie”, the value 7.2 x Ir may be considered the current that the motor absorbs during the starting phase.

The trip classes usually considered and most commonly used are 10A, 10, 20 and 30 referred to as the time “Ti” of the middle column.

It is quite common to speak of normal starting and associate it the trip classes 10A and 10, or heavy starting making reference to trip classes 20 and 30. The other trip classes and the tripping time indicated with band “E” have been recently introduced in an amendment of the Standard IEC 60947-4-1 and are characterized by a restricted trip range due to the increase of the minimum non-tripping time.

The limits fixed for “Ti”, which is the generic tripping time of the thermal protection, have the following meaning:

– The lower limit represents the minimum time under which the relay mustn’t trip in order not to interfere during starting;

– The upper limit is the time within which the relay shall surely trip. Such limit is fixed regarding the standard characteristics of the machine allowing the stator windings, or however the motor in general, to withstand the starting current and the thermal effects generated by the current for quite short times.

Using an easy numerical example, the meaning of the information reported in the table results is clearer. By assuming to have a motor for a specific application that needs a starting time of 5s, the choice of a thermal protection device classified as trip class 10A and 10 would not be correct because, from a theoretical point of view, it could trip already at 2s or 4s; therefore it is necessary to choose a relay in class 20, which up to 6s does not trip, thus allowing complete starting of the motor. The figure below shows a typical example of the protection curves of a relay for motor starting; from their analysis, it is evident the correspondence between the trip time value which “Ti” assumes and the division into the different classes 10A – 10 –20 – 30 which characterizes the relay. It is possible to see how in correspondence with 7.2 x Ir (the value established by the Standard), the relay declared in class 30 has a tripping time of about 23s (item A), thus in compliance with the indications of the table above.

The characteristics of the load to be driven by the motor, the motor type, and the starting modality are elements that influence the starting time and consequently the choice of the thermal protection device. With the only purpose of offering an indication linked to real applications, it is possible to state that ship propellers, compressors, and centrifugal pumps may be included in the category of normal starting, therefore with thermal protection class 10 or 10A, whereas – for example – centrifugal fans, mixers, and mills can be considered part of heavy starting, therefore with thermal protection class 30. It is evident how it is important to define the operating conditions to ensure a correct choice of the motor, and also of the protection device to obtain optimum working and protection conditions.

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trip class 10 vs 20

Overload or Thermal Protection (ANSI 49)

Introduction

Overload or thermal protection protects all types of motor applications against overload currents.

Operating Principle

Overload or thermal protection is I 2 t IDMT (Inverse Definite Minimum Time):

o It incorporates the motor thermal image function.

o It can be configured as the Ir pickup and as the trip class (Class).

Tripping curve:

Ir Pickup Setting Value

The overload or thermal protection pickup (Ir) is set by using a multi-position dial.

The default Ir pickup setting value is 0.4 x In (minimum dial value).

The overload or thermal protection tripping range is 1.05–1.20 x Ir according to IEC/EN 60947-4-1 standard.

The following table shows the preset values of the adjustment dial Ir in amperes for each current rating In:

Trip Class Setting Value

The trip class (Class) is set by using an adjustment dial:

o Class 10 (default value)

The trip class corresponds to the value of the tripping time for a current of 7.2 x Ir according to IEC/EN 60947-4-1 standard.

The following table shows the value of the tripping time depending on the current in the load for all three classes:

The precision range is -20%, + 0%

Motor Thermal Image

The model representing heat rise and cooling in a motor load is constructed according to the algorithm for calculating the thermal demand, taking account of the iron and copper losses.

The following figure represents the limit curves for the iron and copper components calculated for class 20:

Thermal Memory

The trip unit uses a thermal memory function to protect the motor from overheating in case of low amplitude repetitive faults.

Electronic protection without thermal memory function does not protect against repetitive faults because the duration of each overload above the pickup setting is too short to cause tripping. However, each overload causes a temperature rise in the installation. The cumulative effect of successive overloads can overheat the system. The thermal memory function remembers and integrates the thermal heating caused by each pickup setting overrun. The thermal memory function remembers the thermal heating values for 20 minutes before or after tripping.

Example:  Comparison of the heat rise calculation without thermal image (diagram A ) and with thermal image (diagram B ):

With thermal image, the trip unit adds the thermal effect of successive current pulses. Tripping occurs based on the actual thermal state of the motor.

Cooling Fan

The thermal image of the motor is calculated taking account of the fact that the motor is self-cooled (fan mounted on the shaft end).

DOCA0161EN-01

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Nema classes VS Ansi tripping curves

Home » Insights » UL and CSA Conformity » Nema classes VS Ansi tripping curves

Last edit: 16/05/2023

Overload relays typically operate on an inverse time curve where the tripping time becomes less as the current increases. They are rated by trip class. Trip class specifies the length of time it will take for the relay to open in an overload condition.

In Europe the shape of the overload relays tripping curves are defined by ANSI or IEEE standards. A few examples are: ANSI Extremely Inverse, Very Inverse, Inverse, Short Time Inverse; or IEEE Moderately Inverse, Very Inverse and Extremely Inverse.

In North America the NEMA Standard MG-1 defines 4 types of Classes as the most common: 5, 10, 20 & 30. Class 5, 10, 20 & 30 overload relays will trip within 5, 10, 20 & 30 seconds respectively at 600% of motor full load amps.

Class 5 is usually used for motors requiring extremely fast tripping.

Class 10 is commonly used to protect artificially cooled motors such as submersible pump motors of low thermal capacity.

Class 20 is usually sufficient for general purpose applications.

Class 30 is usually required for high inertial loads to help prevent nuisance tripping.

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Overload relay – Principle of operation, types, connection

Every motor must be protected from all possible faults to ensure prolonged and safe operation as well as time loss caused due to breakdown. Almost all industries rely on the electric motor to control their processes and production. Hence it is necessary to make the motor fail-safe.

The most vulnerable part of a motor is its winding insulation. The winding insulations are at high risk of damage by excessively high temperatures. Overload relay is one such device that protects a motor from damage caused due to overloads and over-currents. It is used with contactors and can be found in motor control centers and motor starters.

Thermal Overload relay

Principle of operation

Types of overload relays, working of bimetallic thermal overload relay, working of electronic overload relay, parts of a thermal overload relay, symbol of an overload relay, frequently asked questions, definition of overload relay.

An overload relay is a device that protects an electric motor against overloads and phase failure.

It senses the overloading of the motor and interrupts the power flow to the motor, thus protecting it from overheating and winding damages. Apart from overloads, it can also protect the motor from phase loss/ failures and phase imbalance . They are very commonly known as OLR .

What is an overload?

An overload is a condition at which a motor draws a current above its rated value, for a prolonged period. (adsbygoogle = window.adsbygoogle || []).push({});

It is the most encountered fault and can result in temperature rise in the motor winding. Hence the rapid return to normal operation is important.

A thermal overload relay works in the principle of electro-thermal properties in a bimetallic strip. It is placed in the motor circuit in such a way that the current to the motor flows through its poles. The bimetallic strip gets heated up by the current directly or indirectly and when the current flow exceeds the set value, it bends.

They always work in combination with contactors. When the bimetallic strips heat up, the trip contact is activated that in turn breaks the power supply to the contactor coil, de-energizing it and breaking the current flow to the motor. This tripping time is always inversely proportional to the current flow through the OLR. Hence higher the current flow faster shall it trips. Therefore, thermal overload relays are referred to as current-dependent and inversely time-delayed relays.

Indirectly heated overload relay

Overload relays can be classified as follows:

  • Bimetallic thermal overload relays
  • Electronic overload relays

The working principle of the above differs a little from each other. Let us discuss it in the following sections.

As explained above, a bimetallic thermal relay works on the heating property of the bimetallic strip. In the direct heating method, the full current to the motor flows through the OLR. Therefore, it gets heated up directly by the current.

But in the case of indirect heating, the bimetallic strip is held in close contact with the current-carrying conductor inside the OLR. Excessive current flow to the motor heats up the conductor and hence the bimetallic strip. The conductor shall be insulated hence no current flow through the strip.

Principle of operation of overload relay

Electronic overload relays do not have a bimetallic strip inside. Instead, it uses temperature sensors or current transformers to sense the amount of current flowing to the motor. It uses microprocessor-based technology for protection. Temperature is sensed using PTC and the same is used to trip the circuit in case of overload faults. Some electronic overload relays come with current transformers and Hall effect sensors that directly sense the amount of current flow.

The major advantage of electronic OLR over thermal OLR is that lack of bimetallic strip results in low heat losses inside the relay. Also, Electronic relays are more precise than thermal relays. Some manufacturers build electronic relays with extensive features such as earth fault protection, motor stall protection, etc. Electronic overload relays are much suited for applications that require a frequent start and stop of motors.

In addition, manufacturers offer built-in RTD or thermocouples that can be directly used to measure the winding temperature. These measurements can be used for more accurate thermal overload protection.

They are designed in such a way to withstand the starting current (which is typically 6 to 10 times the full load current) of the motor for a limited period (typically 15-30 seconds depending on the threshold of current).

Parts of an overload relay

Apart from the bimetallic strip and contacts discussed in the working principle section above, there are a few more parts in an overload relay that needs to be understood.

Terminals L1, L2, and L3 are input terminals. It can be directly mounted to the contactor. Supply to the motor can be connected to Terminals T1, T2, and T3.

Ampere range setting

A rotary knob is present over the overload relay. Using this knob, the rated current of the motor can be set. The current can be set between the upper and lower limits provided. In the case of an electronic overload relay, an additional knob for tripping class selection is also provided.

Reset Button

A reset button is present over the overload relay to reset the overload relay after a trip and clearance of fault.

Manual/Auto reset selection

With the manual/auto reset selection button, we can choose between manual and automatic reset of these relays after a trip. If the device is set to auto, a remote reset of OLR is possible.

Auxiliary contact

They are provided with two auxiliary contacts – one NO (97-98) and another NC (95-96). NO contact is for trip signaling and NC contact is for disconnecting the contactor. NC contacts should be capable of direct switching of contactor coil.

Test button

Using the test button, it is possible to test the control wiring.

Symbol of an overload relay

Here 1, 2, 3, 4, 5 and 6 are power terminal 95 & 96 are trip contacts and 97 & 98 are signaling contacts. Learn how to use them in a circuit here: Star-Delta starter wiring diagram – Control and power wiring diagrams

What is the trip Class of overload relay?

The time taken by them to open the contactor during overloads is specified by the trip class . It is commonly classified into Class 10, Class 20, Class 30, and Class 5. The OLR trips in 10 seconds, 20 seconds, 30 seconds, and 5 seconds respectively at 600% of full load current to the motor.

Class 10 and Class 20 are very commonly used ones. Class 30 overload relays are used for the protection of motors driving high inertia loads and Class 5 relays are used for the motors requiring very fast tripping.

Trip class curve

How to use an overload relay in a circuit?

They are always used in combination with the contactors in the circuit. It is connected in line with the motor such that the current to the motor fully flow through it. Below are the various types of connections for single-phase and three-phase motors.

DOL starter with overload relay

Read more: Sizing of contactor and overload relay for 3 Phase DOL starter Read more on star delta starters: Star-delta starter (Wye-Delta Starters) – Circuit, working . Read more about contactors: Contactor – Construction, Operation, Application and Selection

What causes the OLR trip?

As discussed above, there are three major conditions for overload trips :

  • Overloading of the motor.
  • Input phase loss
  • Phase imbalance.

Apart from these, there may be some additional protection features available. This varies from one manufacturer to the other.

How does an overload relay protect from phase failures?

During normal operation, the current flowing through each pole of an overload relay to the motor remains the same at a time. If anyone of the phase is interrupted, the current through the other two phases rises to 1.73 times the normal value. Hence the overload relay gets heated up and it trips. Phase failure is also known as single phasing of motor or phase loss.

Phase loss in overload relay

Can OLR protect from short circuits?

Overload relays cannot protect against short circuits. They should always be used with short circuit protection devices. Otherwise, any short circuits in the motor can potentially damage them. They can protect against overloads, phase loss, and phase imbalance, but not short circuits.

What could damage an overload relay?

The device will be damaged if the backup short circuit protection device (circuit breaker or fuse) is overrated. This may also damage the whole starter and even the motor windings themselves. Therefore it is advised to stick on to the maximum short circuit protection advised by the relay manufacturer.

An overload relay is a device that can protect a motor from overloads, phase failure, and phase imbalances. Based on the principle of operation they are classified into thermal and electronic overload relays. Thermal OLR is based on the principle of deformation of a bimetallic strip on heating. The electronic overload relay is a microprocessor-based device and comes with extensive built-in functionalities.

OLRs are used in combination with the contactors. It opens the contactor whenever it senses a fault. The time taken by them in opening the contactor during overloads is specified by their trip class. Overload relays cannot protect against short circuits. This sample datasheet can help you understand the relay ratings. They could be easily damaged if underrated or under with an overrated short circuit protection device (Fuse or Circuit breaker).

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What is the difference between Class ratings on overload relays?

Posted by Jim Lloyd on Oct 25th 2018

You may have sent overload relays with different Class ratings.  Class 10 and Class 20 tend to be the most common there is also a Class 5 rating and a Class 30.   So what does the difference mean? Simply put the Class rating specifies in what amount of time the overload will trip after it is in an over amperage situation.  For example, a Class 10 overload will trip in 10 seconds or less (depending on the percentage variation of AMP pull) and a Class 20 will trip in 20 seconds or less.

So why is this important and how do you know which to choose?  Class 10 is the most common as it provides a high level of protection for the motor, which is the main function of a  contactor with overload relay protection.  Class 20 is used in situations where you want to avoid nuisance tripping.  Let's say you have a motor with a high inrush that maintains a AMP pull that can last 10-15 seconds.  If you use a Class 10 overload relay, it would trip even though there is not potential damage to the motor.  A Class 20 overload would allow for a little extra time for that motor to level it's AMP draw.

So to sum up, Class 10 overloads are the most common as they provide a high level of protection for a motor while Class 20 overloads are used in situations where nuisance tripping is an issue.

  • #Class 10 Overload Relays
  • #Class 20 Overload Relays
  • #Nuisance Tripping
  • #Solid State Overload Relays
  • #Thermal Overload Relays

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Home > Protection > Tripping Curves of Circuit Breakers – B, C, D, K and Z Trip Curve

Tripping Curves of Circuit Breakers – B, C, D, K and Z Trip Curve

Types of circuit breaker based on its tripping curve.

A circuit breaker is a protection device employed in every electrical circuit to prevent any potential hazard. There are different types of circuit breakers used all over the world due to their various characteristics & applications. It is necessary to have a circuit breaker that offers adequate protection so that one can work safely around it without having fear of any potential hazards. That is why it is best to know about these kinds of circuit breakers & what kinds of protection do they offer before buying one.

Table of Contents

What is a Circuit Breaker?

A circuit breaker is an electrical device that provides protection against fault current. It breaks the circuit in case of overloading & short circuit. The fault currents generated due to these fault conditions can damage the electrical devices as well as cause fire in a building that can also pose danger to human life.

The circuit breaker instantly cut off the power supply to reduce further damage. A circuit breaker has two types of tripping unit i.e. thermal and magnetic tripping unit.

Thermal Tripping Unit: the thermal tripping unit is used for protection against overloading. It uses a bi-metallic contact that bends with a change in temperature. The current flowing through the bimetallic strip heats up contact & trip the circuit breaker.

The rate of bending of the bi-metallic strip depends on the amount of current. Therefore, greater the overloading current, faster the circuit breaker trips.  

Magnetic Tripping Unit: The magnetic trip unit is used for protection against short circuit current. it includes a solenoid that produced a strong magnetic field due to high short circuit current to instantly trip the circuit breaker.

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trip class 10 vs 20

What is a Trip Curve?

A trip curve also known as a current time graph is a graphical representation of the response of a circuit breaker. It shows the current relationship with the tripping time of a protection device.

Why We Need Different Tripping Curves?

Circuit breakers are used for tripping the power supply as quickly as possible in case of overcurrent. But it should not trip so fast & unnecessary that it becomes a problem.

The overcurrent can happen under normal conditions such as the inrush current of a motor. Inrush current is the huge current draw during the starting of a motor that causes voltage dips in the main line. The circuit breaker should be able to tolerate the inrush current & it should provide some delay before tripping.

Therefore, the circuit breaker selected should not trip so fast that it creates a nuisance & it should not trip so late that it causes any damage. This is where the tripping characteristics of the circuit breakers come into play.

The tripping curve tells how fast a circuit breaker will trip at a specific current. The different tripping curves classify the circuit breakers into categories where each category is used for specific types of loads. It is essential to select a circuit breaker that provides the necessary overcurrent protection.

  • Types of Circuit Breakers – Working and Applications
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How to read a Trip Curve?

The following figure shows a chart of a trip curve.

The horizontal X-axis represents the multiples of the current flowing through the circuit breaker. While the Y-axis represents the tripping time of the circuit breaker on a logarithmic scale.

Tripping Curve

The thermal region shows the response of the bimetallic contact trip unit during overcurrent. The curve shows that the circuit breaker’s tripping time reduces with an increase in the current. The first curve in the graph shows the response of a thermal trip unit.

While the magnetic region shows the response of the solenoid to fault current such as a short circuit current.

As seen from the graph, a circuit breaker does not have a fixed tripping time and we cannot predict an exact tripping point. It is because the tripping is affected by ambient conditions such as temperature. Think of it as a Schrödinger’s Cat area, we do not know when the tripping will occur unless the event happens. 

Types of Circuit Breaker Based on Tripping Curves

The circuit breakers are classified into the following five types based on their tripping curves.

Tripping Curve of Circuit Breakers

Such type of circuit breaker is designed to instantly trip when the operating current is 3 to 5 times its rated current. Their tripping time falls between 0.04 to 13 seconds. They are suitable for domestic applications where surges are very low such as lighting & resistive loads.

Type B Trip Curve

They are sensitive and must not be used in places where the normal surges keep on tripping it unnecessarily.

Type C circuit breaker trips instantly at current surges 5 to 10 times its rated current. its tripping time lies between 0.04 to 5 seconds. As they can tolerate higher surge currents, they are used in commercial applications such as the protection of small motors, transformers, etc.

Type C Trip Curve

Type D circuit breaker trips instantly when operating current reaches 10 to 20 times its rated current. Its tripping time is 0.04 to 3 seconds. Such circuit breakers can tolerate the high inrush current of large motors. Therefore, they are suitable for running heavy loads in industrial applications.

Type D Trip Curve

Such type of circuit breakers trips at 10 to 12 times its rated current with a tripping time of 0.04 to 5 seconds. These circuit breakers are also used for heavy inductive loads in industrial applications.

Type K Trip Curve

Type Z circuit breakers are the most sensitive circuit breaker that instantly trips when the operating current reaches 2 to 3 times its rated current. They are used for sensitive equipment that requires very low short circuit trip settings. 

Type Z Trip Curve

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IMAGES

  1. IEC60947-4-1 tripping time curves as a function of actual to full-load

    trip class 10 vs 20

  2. Overload relay

    trip class 10 vs 20

  3. Full-featured Soft Starter: 124A, Trip Class 10/20/30 (PN# SR55-124

    trip class 10 vs 20

  4. Basic Soft Starter: 55A, Trip Class 10/20/30 (PN# SR33-55

    trip class 10 vs 20

  5. Full-featured Soft Starter: 302A, Trip Class 10/20/30 (PN# SR55-302

    trip class 10 vs 20

  6. What does the Trip Class 10, Class 20, and Class 30 mean for overload

    trip class 10 vs 20

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COMMENTS

  1. What is Trip Class? Trip Class 5, 10, 10A, 20, 30, 40 Explained

    Trip classes according to NEMA. NEMA Standard MG-1 defines 4 types of Classes. The most common classes are 5, 10, 20 & 30. Class 5, 10, 20 & 30 overload relays will trip within 5, 10, 20 & 30 seconds respectively at 600% of motor full load amps. A Class 10 overload relay, for example, has to trip the motor offline in 10 seconds or less at 600% ...

  2. What does the Trip Class 10, Class 20 and Class 30 mean for overload

    Issue: Meaning of Trip Classes for overload relays. Product Line: NEMA Overload Relays Environment: North American Products Resolution: The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 ...

  3. Overcurrent Protection: Motor Starter Trip Classes for Industrial

    The time for which the OL should pause before reacting will be different for various motors and applications is called the motor trip class. The most common trip classes are 5, 10, 20, and 30, which refer to the number of seconds for which the OL will allow this 600% current in-rush. Applications for each of these trip classes can be classified ...

  4. PDF Low voltage Motor Protection

    The most common trip classes are Class 10, Class 20, and Class 30. A Class 10 overload relay, for example, has to trip the motor offline in 10 seconds or less at 600% of the full load amps (which is usually sufficient time for the motor to reach full speed). Many industrial loads, particularly high inertia loads, require Class 30.

  5. Overload or Thermal Protection (ANSI 49)

    The trip class (Class) is set by using an adjustment dial: o Class 5 . o Class 10 (default value) o Class 20. The trip class corresponds to the value of the tripping time for a current of 7.2 x Ir according to IEC/EN 60947-4-1 standard. The following table shows the value of the tripping time depending on the current in the load for all three ...

  6. Nema classes VS Ansi tripping curves

    In North America the NEMA Standard MG-1 defines 4 types of Classes as the most common: 5, 10, 20 & 30. Class 5, 10, 20 & 30 overload relays will trip within 5, 10, 20 & 30 seconds respectively at 600% of motor full load amps. Class 5 is usually used for motors requiring extremely fast tripping. Class 10 is commonly used to protect artificially ...

  7. Overload Trip Class

    Quite often we here of applications in which the motor protection/overload relay 'trips' during normal motor starting. The remedial action taken by many when faced with this problem is to select and install a replacement overload relay, generally one that provides a higher 'Trip Class' setting, for example, Trip Class 20 in lieu of the standard Trip Class 10.

  8. The Basics Of Selecting Overload Relays

    An unmarked overload relay is always Class 20. Typical NEMA-rated overload relays are Class 20, but you can adjust many of them about 15% above or below their normal trip current. IEC relays are usually Class 10, and you can usually adjust them to 50% above their normal trip current. When replacing overload heaters, always replace the entire set.

  9. What calculations determine the choice of the overload relay trip class

    The motor trip current does not determine the choice of trip class. Trip class specifies the length of time it will take for the relay to open in an overload condition. Classes 5, 10, 20 & 30 are the most common. Class 5, 10, 20 & 30 overload relays will trip within 5, 10, 20 & 30 seconds respectively at 600% of motor full load amps.

  10. Overload relay

    What is the trip Class of overload relay? The time taken by them to open the contactor during overloads is specified by the trip class. It is commonly classified into Class 10, Class 20, Class 30, and Class 5. The OLR trips in 10 seconds, 20 seconds, 30 seconds, and 5 seconds respectively at 600% of full load current to the motor.

  11. What does the Trip Class 10, Class 20 and Class 30 mean for overload

    Issue: Meaning of Trip Classes for overload relays. Product Line: NEMA Overload Relays Environment: North American Products Resolution: The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 ...

  12. PDF Soft Start and Star Delta Trip Class by Application Chart

    Trip Class Explained At between 500% & 600% of the maximum current rating of the motor during application starting, the Trip Class 10 motor thermal overload will trip in 10 seconds or less, Trip Class 20 motor thermal overload will trip in 20 seconds or less, and Trip Class 30 motor thermal overload will trip in 30 seconds or less.

  13. PDF Tripping Class 20

    Class 10 4 - 10 sec 1.2 Ie 7.2 Ie Class 20 6 - 20 sec Class 30 9 - 30 sec TA25DU trip class 20 for contactors A9 … A40 and (T) AL9 … (T) AL30 TA25DU1.8-20 1SAZ211401R1025 1.3 … 1.8 6 1 $ 63 TA25DU2.4-20 1SAZ211401R1028 1.7 … 2.4 10 1 TA25DU3.1-20 1SAZ211401R1031 2.2 … 3.1 10 1 TA25DU4.0-20 1SAZ211401R1033 2.8 … 4.0 15 1

  14. Set CORRECT Overload Relay SETTING

    Understanding of overload relay trip class 10 /20 /30 is very important for correct setting of thermal overload relay. This concept has been discussed in hi...

  15. What does the Trip Class 10, Class 20 and Class 30 mean for overload

    The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 seconds or less. Published for: Schneider Electric Saudi Arabia

  16. What is the difference between Class ratings on overload relays?

    A Class 20 overload would allow for a little extra time for that motor to level it's AMP draw. So to sum up, Class 10 overloads are the most common as they provide a high level of protection for a motor while Class 20 overloads are used in situations where nuisance tripping is an issue. #Class 10 Overload Relays. #Class 20 Overload Relays.

  17. NEMA standards for overload protection need closer look

    Note that a Class 10A IEC overload is different from a Class 10 IEC overload relay, which can trip in 4 min at 150% of motor current. This, in turn, is less than IEC Class 20 or Class 30 overloads, which can trip at 8 min or 12 min, respectively. An additional point of confusion is that NEMA and IEC overload class characteristics are inconsistent.

  18. What does the Trip Class 10, Class 20 and Class 30 mean for overload

    Issue: Meaning of Trip Classes for overload relays. Product Line: NEMA Overload Relays Environment: North American Products Resolution: The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 ...

  19. PDF Tripping Class 20

    Thermal overload relays are 3 pole. The motor current flows through their bimetals (1 per phase) which are indirectly heated. Under the effect of the heating, the bimetals bend, cause the relay to trip and the position of the auxiliary contacts to change. The relay setting range is graduated in amps. In compliance with international and ...

  20. Tripping Curves of Circuit Breaker. B, C, D, K & Z Trip Curve

    A circuit breaker has two types of tripping unit i.e. thermal and magnetic tripping unit. Thermal Tripping Unit: the thermal tripping unit is used for protection against overloading. It uses a bi-metallic contact that bends with a change in temperature. The current flowing through the bimetallic strip heats up contact & trip the circuit breaker.

  21. What does the Trip Class 10, Class 20 and Class 30 mean for overload

    Issue: Meaning of Trip Classes for overload relays. Product Line: NEMA Overload Relays Environment: North American Products Resolution: The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 ...

  22. What does the Trip Class 10, Class 20 and Class 30 mean for overload

    The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 seconds or less. Đã phát hành cho: Schneider Electric Việt Nam

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    NEMA Overload Relays. Environment: North American Products. Resolution: The trip class means that at 600% (6 times) of the maximum thermal current rating (or 600% of the actual dial setting on adjustable overloads) the Class 10 will trip in 10 seconds or less, Class 20 will trip in 20 seconds or less, and Class 30 will trip in 30 seconds or less.