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Thermal relay outlet terminal connection wire selection

2021-04-25

The thermal relay should be installed below other heating appliances. The setting of the current device should generally be installed on the right side and ensure safety and convenience in making adjustments and resets. When connecting, the connection point should be tight and reliable, and the wire at the outlet end should not be too thick or too thin to prevent the axial heat conduction from being too fast or too slow, so that the thermal relay does not operate accurately. The precautions for the installation and use of thermal relays are as follows:

1) The installation direction and method should meet the requirements of the manual. The inclination should be less than 5°, preferably installed under other electrical appliances. The outlet wire should be selected according to the table to ensure accurate operation.

Table thermal relay outlet end connection wire selection table

Thermal relay rated current (A) Connecting wire cross-sectional area (mm2) Connection wire type
10 2.5 Single strand copper core plastic wire
20 4 Single strand copper core plastic wire
60 16 Multi-strand copper core rubber cord
150 35 Multi-strand copper core rubber cord

2) For motors such as jog, heavy load starting and reverse braking, it is not advisable to use thermal relay for overload protection. The cover should be covered during installation, the wiring should be secure, and all dirt should be eliminated and carried out regularly.

3) Check if the thermal element is good, do not remove it, and conduct a power-on experiment if necessary. The capacity of the heat element is compatible with the load of the protected circuit, and the position of each component must not be changed arbitrarily; check the ambient temperature around the heat element and the ambient temperature around the Motor. If the former is 15 to 25 °C higher than the latter, a higher thermal element should be used. If the temperature is lower than 15 ~ 25 ° C, the lower level of thermal components should be used.

4) When the thermal relay is running, except for the temperature difference, the ambient temperature is required to be in the range of -30 to +40 °C; check whether there is unreasonable heating phenomenon at the connection end.

For the selection of the connection wire of the thermal relay outlet end. Must be selected in strict accordance with the regulations. This is because the material of the wire and its wire diameter can affect how much heat is transferred from the end of the heating element to the outside. If the wire is too thin, the axial heat conduction is poor, and the thermal relay may move in advance; otherwise, the wire is too thick, the axial heat conduction is fast, and the thermal relay may delay the action.

According to the regulations: the wire connecting the outlet of the thermal relay should be copper wire. If the wire is to be used, the cross-sectional area of ​​the wire should be enlarged by 1.8 times. In addition, the outlet end screw should also be tightened to prevent the contact resistance from increasing due to the looseness of the screw, affecting the temperature rise of the heating element, and eventually the protection characteristics may be unstable and cause malfunction.

General thermal relay connecting wires can be selected as follows:

(1) When the rated current of the thermal relay is below 10A, 2.5mm2 single-core plastic copper wire can be used.

(2) When the rated current of the thermal relay is below 20A, 4mm2 single-core plastic copper wire can be used.

(3) When the rated current of the thermal relay is 60A, 16mm2 multi-strand rubber core cord can be used.

(4) When the rated current of the thermal relay is 150A, a 35mm2 multi-strand rubber core cord can be used.

It should be noted that the connecting wires of the thermal relay also have a heat conduction function in addition to being electrically conductive. Therefore, the connecting wire should not be too thin to prevent the heat from being too fast.


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