3 Thermal Relay Manufacturers in 2023
This section provides an overview for thermal relays as well as their applications and principles. Also, please take a look at the list of 3 thermal relay manufacturers and their company rankings.
Table of Contents
What Is a Thermal Relay?
A thermal relay is a component that outputs a contact when a current exceeding a set value flows into an electrical circuit. They are mainly used to prevent overloading of motors and wiring. By incorporating thermal relay into circuits, problems such as circuit burnout can be prevented.
Uses of Thermal Relays
Thermal relays are mostly used for motor protection. When a motor is subjected to a torque in excess of its rating, a current in excess of the rating will flow. This phenomenon is called overcurrent.
When a motor is in an overcurrent state for an extended period of time, the internal windings heat up. This causes the internal varnish to melt or the windings to burn out. This is called motor burnout. When a current exceeding the rated value flows, the thermal relays shuts off the power supply by means of a contact output to protect the motor.
Principle of Thermal Relays
In most cases, bimetals are used as circuit conductors inside thermal relays. Bimetal is a material that combines two types of metals with different coefficients of thermal expansion. When heat is generated by an electric current, it is biased and deformed due to the difference in thermal expansion coefficients.
The bimetal inside the thermal relays uses this bias to drive the contact point and output the contact. Thermal relays are available with different current settings depending on the thickness of the bimetal and other factors.
When a motor starts, the current is more than twice the rated value. Since the bimetal heats up and deforms, there is a delay time until it warms up. Due to this delay time, they do not react to the high starting current of the motor.
The output contact of a thermal relays are fixed by a spring, and once activated, in most cases the output continues to be output until the reset button is pressed. This prevents overloaded equipment from restarting.
How to Select a Thermal Relays
Thermal relays are selected according to the current rating of the motor to be protected. There are two types of motor protection elements: instantaneous and time-limited.
The momentary element is a protective element that shuts off the motor power supply instantaneously to protect the upper circuit in the event of a motor malfunction. Power fuses and motor relays are used for high-voltage motors, while shock relays and breakers are mainly used for low-voltage motors.
A time-limiting element is a protective element that detects motor overload and shuts off the power supply to protect the motor. Overcurrent relays are used for high-voltage motors, and thermal relays are used for low-voltage motors.
For low-voltage motors, a breaker, drive unit, and thermal relays should be selected in conjunction with the above. The breaker should be at least twice the motor's rated current to avoid tripping due to starting current. The drive and thermal relays should be selected according to the motor's rated current, referring to the manufacturer's catalog.
Other Information on Thermal Relays
1. Thermal Relays Settings
Thermal relays are classified into two types: bimetal type and electronic type.
- Bimetal type
In the bimetal type, the relay is operated by thermal expansion of the bimetal. In the case of the bimetal type, the current value can be set by ±20% by turning the setting knob.Further setting changes are structurally impossible, so the relay must be replaced. If the device to be protected is a motor, check the manufacturer's catalog for thermal relays suitable for the motor capacity. - Electronic Type
The electronic type is used when the drive to be protected is an inverter. The electronic circuit reads the current value flowing in the circuit and operates when it deviates from the load characteristic curve. Most inverters on the market are equipped with this function as an inverter protection function. Electronic thermal relays are also used in motor control centers. The setting method for electronic thermal relays varies from manufacturer to manufacturer, but the lower current limit can be set more widely than that of the bimetal type. Check the instruction manual for the setting. Normally, the setting is done automatically by setting the rated current value.
2. Thermal Relays Contacts
The thermal relays has two types of contacts: a normally open contact (a-contact) for monitoring and a normally closed contact (b-contact) for breaking the circuit.
- Bimetal Contacts
In the case of the bimetal type, the number of which to use must be selected at the purchase stage. The current rating for the contacts is determined by the relay and is usually around 2A. Since there is a high risk of welding if they are used in the main circuit, they are used for control circuits. - Electronic Contacts
In many cases, electronic thermal relays can be set to use any number of contacts. However, electronic types may have transistor contacts instead of relay contacts. With transistor contacts, the electronic components will fail if an AC control power supply is used.
3. Return of Thermal Relays
When an overload condition persists and the thermal relays operates, the output contact of the thermal relays must be deactivated after the cause is removed. This procedure is called "recovery" or "resetting".
There are two types of reset procedures: manual reset and automatic reset. The manual return type is simple, press the reset button after removing the cause of the overload. By pressing the reset button, the output contact is released.
The automatic reset type does not require pressing the reset button, but the thermal relays itself automatically resets itself. It is used in special applications where it is difficult for people to approach the thermal relays
4. Thermal Relays Deterioration Factors
Although it varies from manufacturer to manufacturer, the recommended replacement period for thermal relays is approximately 10 years. However, since periodic replacement of thermal relays are costly, in most cases only periodic replacement of thermal relays for critical loads is required.
Since thermal relays are composed of bimetals and resins, which do not deteriorate easily, they rarely deteriorate naturally. The following four factors are known to cause forced deterioration.
- Electrical Factors
Insulation degradation occurs depending on the magnitude and frequency of drive voltage, frequency, and inrush current. This causes the thermal relays to fail. - Mechanical Factors
Physical factors such as loosening of screws, shock, and vibration can cause deterioration such as metal fatigue. - Thermal Factors
Thermal factors such as overvoltage, overcurrent, and self-heating cause thermal relays to warp, deform, or melt and break, resulting in failure. - Environmental Factors
Metal corrosion is caused by high temperature, high humidity, corrosive gases, oil mist, etc. Dust and foreign matter can also bite into the thermal relays, resulting in poor contact. By understanding the causes of deterioration and avoiding these factors, it is possible to extend the life of the product by the user.
5. Wiring of Thermal Relays
Thermal relays are often used as part of electromagnetic switches. In such cases, the primary side of the main circuit is usually connected with a copper bar for power supply in commercial products. The secondary side wiring should be designed to have an allowable current greater than the rated current of the thermal relays.
The allowable current for wiring varies depending on the type of wiring, but each type is defined by the internal wiring regulations. Wiring sold in Japan complies with the extension regulations.
List of 3 Thermal Relay Manufacturers
*Including some distributors, etc.
Sort by Features
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- Company Size: largest first
- Year Founded: oldest first
- Year Founded: earliest first
Sort by Area
- United States of America
- France
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Eisen Machinery Inc.
Thermal Overload Relay
Company Overview
Eisen Machinery Inc. is an importer and distributor of precision industrial machinery and machine components headquartered in Ontario, California. Established in 2002, their distribution includes machine tools such as grinders, milling machines, and engine lathes, as well as machine parts like forward reverse switches and power feeds. The company primarily serves machinery and equipment manufacturers as well as wholesalers in the energy, automation, and security industries. With partners in over three continents, Eisen Machinery Inc. can supply machinery and parts from Germany, Taiwan, and Japan, as well as accommodate custom orders for items not currently available.
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Schneider Electric
Motor Protection Overload Relays
Company Overview
Schneider Electric S.E. is headquartered in Rueil-Malmaison, France, and has been operating since 1836. Schneider Electric provides a number of products and services including electrical car charging, energy management software, surge protection devices, load banks, servers and HMIs, valve and valve actuators, feeder automation, grid automation, and SCADA software products, data center cooling and software, home automation and security, light switches, motion control and robotics, signaling units, solar and energy storage, RFID systems, as well as other hardware, services, and software.
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Thermal Relay Manufacturer Ranking
*Including some distributors, etc.Ranking as of June 2023 Globally
Derivation Method| Rank | Company | Click Share |
|---|---|---|
| 1 | Eisen Machinery Inc. | 50% |
| 2 | Legrand | 50% |
Derivation Method
The ranking is calculated based on the click share within the thermal relay page as of June 2023. Click share is defined as the total number of clicks for all companies during the period divided by the number of clicks for each company.Number of Employees
Newly Established Company
- Legrand: 1904 (119 years ago)
- Schneider Electric: 1871 (152 years ago)
Company with a History
- Schneider Electric: 1871 (152 years ago)
- Legrand: 1904 (119 years ago)
