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What Means Ith2?

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Hi, can any one tell me what Ith2 means? Wen i read the nameplate in a contactor, for example in AC3 for 380V it has 7.5 kw, but it also say in an aother part in the nameplate Ith2 = 30 amps. I usually use this contactor for 15 amps in an AC three phase motor. Is Ith2 the max amps that the contactor can handl? Is the breaking current?


Thanks in advance for any help.



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Another way to look at it is that is the Thermal current (hence the "th" in the designation). So you can use that value for things such as resistive heating or incandescent lighting loads, but not switching of inductive loads such as motors. You can however use that value when applying a contactor as a bypass for a soft starter, as long as you never want to use the contactor to start the motor in an emergency.
"He's not dead, he's just pinin' for the fjords!"
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The thermal current of a contactor or switch is the maximum continuous current that can be passed through the contacts on that switch. There must not be any overload current.

The life of the contacts is temperature related and the power dissipated is proportional to the square of the current.

If there is an overload current, the power dissipated during the overload is much higher than the steady state current and consequently, the contact temperature is elevated.

In order to limit the maximum temperature of the contacts, current ratings where overloads occur, AC2, AC3, AC4 etc currents are reduced.

An AC3 current rating is based on motor starting applications and so the continuous current is much less than the continuous thermal current (AC1).


Best regards,

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