JR28F 53-630A Thermal Overload Relay

General

JR28F series thermal overload relays provide overload and phase loss protection for AC motors. They are suitable for 50/60 Hz circuits, rated voltage up to 690 V, and rated current from 51 A to 630 A, for 8‑hour duty or continuous duty. These relays feature phase‑loss protection, ON/OFF indication, temperature compensation, and manual/automatic reset functions. Standards: IEC 60947‑4‑1  

Type designation

Thermal Overload      Relay	Design Serial Number	Frame	Adjustable Current Range
JR	28F	400/630	259-414A
Thermal Overload Relay	Design Serial Number	400/630	51-81A 62-99A 84-135A 124-198A 146-234A 174-279A 208-333A 259-414A 321-513A 394-630A

 

Operating condition

1. Ambient temperature: ‑5°C~+40°C 2. Relative humidity: ≤50% at 40°C; ≤90% at 20°C 3. Altitude: ≤2000m 4. Environmental conditions: no harmful gases and vapors, no conductive or explosive dust, no severe mechanical vibration  

Technical data

Model	Rated Insulation Voltage Ui	Setting Current Adjustment Range (A)	Matching Contactor CJX2-F Series
JR28F-400	660	51-81	CJX2-F115 CJX2-F150
		62-99
		84-135
		124-198	CJX2-F185
		146-234	CJX2-F225 CJX2-F265 CJX2-F330
		174-279
		208-333
		259-414	CJX2-F400
JR28F-630	660	321-513	CJX2-F500
		394-630	CJX2-F630

 

Model	Rated Insulation Voltage Ui	Setting Current Adjustment Range(A)	Matching Contactor YCC7/CJX2s Series
JR28F-400	660	51-81	YCC7/CJX2s-115 YCC7/CJX2s-150 YCC7/CJX2s-170 YCC7/CJX2s-120 YCC7/CJX2s-160
		62-99
		84-135
		124-198
		124-198	YCC7/CJX2s-185 YCC7/CJX2s-225 YCC7/CJX2s-265
		146-234
		174-279
		124-198	YCC7/CJX2s-330 YCC7/CJX2s-400 YCC7/CJX2s-500
		146-234
		174-279
		208-333
		259-414
JR28F-630	660	321-513	YCC7/CJX2s-330 YCC7/CJX2s-400 YCC7/CJX2s-500 YCC7/CJX2s-630
		394-630

 

Structural Characteristics and Working Principle

1. The setting current is continuously adjustable; 2. Equipped with temperature compensation, with an ambient temperature upper limit of +40°C and a lower limit of -5°C; 3. Both auxiliary circuit terminals and main circuit outgoing terminals are equipped with protective covers; 4. Equipped with action indication, manual reset device and stop function; 5. Equipped with a locking device to prevent misoperation; 6. Normally open and normally closed auxiliary contacts are insulated and separated.   Working Principle The thermal overload relay adopts a front‑rear overall structure, and its main components include: heating elements, auxiliary contacts, action system and reset mechanism. The heating elements and transformers are connected to the main circuit, through which the current of the motor flows. When the motor is overloaded, the main bimetallic strip is heated to the action temperature, causing the thermal overload relay to act, the normally closed contacts open, and the contactor cuts off the main circuit. The action time of the thermal overload relay changes with the magni‑tude of the overload current according to an inverse time‑limit relationship. The typical working principle diagram of the thermal overload relay is shown in Figure 1. If it is used for overload protection in AC single‑phase or DC circuits, the three‑phase heating elements must be connected in eries.  

Basic Parameters of Auxiliary Contacts

Usage Category	Rated Frequency(Hz)	Conventional Free Air Thermal    Current Ith (A)		Rated Insulation Voltage Ui (V)	Rated Working Voltage Ue(V)	Rated Working Current le(A)
		Normally Open	Normally Closed
AC-15	50	5	5	380	220	2.73
					380	1.58
DC-13					220	0.21
					110	0.46

 

Operating Characteristics When Each Phase Load is Balanced

No.	Setting Current Multiple	Operating Time	Initial Condition	Ambient Air Temperature
1	1.05	No action within 2h	Starting from cold state	20±5℃
2	1.2	Action within 2h	Starting from hot state(after test No.1)
3	1.5	Action within 2min
4	7.2	2s<Tp≤10s	Starting from cold state

 

Operating Characteristics When Each Phase Load is Unbalanced (Phase Loss)

No.	Setting Current Multiple		Operating Time	Initial Condition	Ambient Air Temperature
	Any Two Phases	The Other Phase
1	1	0.9	No action within 2h	Starting from cold state	20±5℃
2	1.15	0	Action within 2h	Starting from hot state(after test No.1)

 

Temperature Compensation Performance

No.	Setting Current Multiple	Operating Time	Initial Condition	Ambient Air Temperature
1	1	>2h	Starting from cold state	+40℃
2	1.2	<2h	Starting from hot state (after test No.1)
3	1.05	>2h	Starting from cold state	-5℃
4	1.3	<2h	Starting from hot state (after test No.3)

1. The manual reset time after the thermal overload relay trips shall not exceed 5 minutes, and the automatic reset time shall not exceed 10 minutes. 2. The power frequency withstand voltage of the thermal overload relay is 2500V for the main circuit and 2000V for the auxiliary circuit.  

Overall and mounting dimensions(mm)

AFD9-63 offers maximum protection against:

Specification Model	Rated Current(A)	A	B	C	D	E	F	G1	G2	P	Q	R	S	T	Mounting Base
JR28F-400	51-81	34.8	55.5	182	32	119	141	144	156	9	63	18	3	164	LAES1
	62-99	34.8	55.5	182	32	119	141	144	156	9	63	18	3	164
	84-135	34.8	55.5	182	32	119	141	144	156	9	63	20	3	164
	124-198	40	55.5	182	32	109	131	144	156	10	63	25	3	164
	146-234	48	55.5	182	32	109	134	144	156	12	63	25	3	164
	174-279	48	55.5	182	32.5	109	134	144	156	12	63	25	3	164
	208-333	48	55.5	182	32.5	109	134	144	156	12	63	25	4	164
	259-414	48	55.5	182	32.5	109	134	144	156	12	63	25	4	164
JR28F-630	321-513	55	76	242	43	110	140	158	170	14	77	30	5	222	LAES2
	394-630	80	80	242	43.5	114	150	158	156	14	77	40	6	222

 

For the selection of connecting wires for the main circuit of the thermal overload relay, the screws of the connecting wires shall be tightened without looseness, and the tightness shall be checked regularly during use; otherwise, the thermal overload relay may lose its protective effect.

Current Range(A)	Standard Cross-Sectional Area of Wire(mm²)	Wire Length Between Two Terminals (m)
80<le≤125	50	2.0
100<le≤160	70	2.0
125<le≤200	95	2.0

 

FAQ - JR28F Series

1. What is a JR28F Thermal Overload Relay?

The JR28F series thermal overload relays are specialized protective devices designed to provide reliable overload and phase loss protection for AC motors. They are critical for ensuring system safety in professional motor control applications.

2. What are the primary protection functions of the JR28F series?

The JR28F provides advanced protection against motor overloads and phase failure. It also features built-in temperature compensation to ensure consistent performance across varying environmental conditions.

3. What are the rated voltage and current ranges for this series?

This series is designed for 50/60 Hz circuits with a rated insulation voltage of 660V and a maximum operating voltage of 690V. The adjustable current range is exceptionally broad, spanning from 51A up to 630A.

4. How does the thermal overload relay work?

When a motor experiences an overload, the main bimetallic strip inside the relay heats up and bends. Once it reaches the action temperature, the relay triggers, causing the normally closed (NC) contacts to open and signaling the contactor to disconnect the power.

5. Does the JR28F include ambient temperature compensation?

Yes. The relay is engineered with temperature compensation technology, allowing it to maintain precise tripping characteristics even when ambient temperatures fluctuate between -5°C and +40°C.

6. How can the relay be reset after a trip occurs?

The JR28F offers both manual and automatic reset modes. For safety and operational flexibility, manual resets take no more than 5 minutes, while automatic resets are completed within 10 minutes.

7. Which contactors are compatible with the JR28F-400 and 630 models?

The JR28F-400 series is designed to match CJX2-F contactors (F115 to F400), while the JR28F-630 model is optimized for larger units like the CJX2-F500 and F630. It is also compatible with the YCC7/CJX2s series.

8. Can this relay be used for single-phase or DC motor protection?

Yes, it can. To use the JR28F for overload protection in AC single-phase or DC circuits, the three-phase heating elements must be connected in series to ensure the relay detects the current correctly.

9. What international standards does the JR28F comply with?

The JR28F series is manufactured and tested in strict accordance with the IEC 60947-4-1 international standard, ensuring high-quality performance for global industrial markets.

10. What are the critical maintenance requirements for the main circuit?

It is vital to ensure all connecting wire screws are tightened securely. Loose connections can cause localized heating and prevent the relay from providing effective protection, potentially leading to equipment failure.