Contact capacity

The so-called contact capacity refers to the voltage and current values that can be passed through; below these values, the contacts will not suffer from welding. 250VAC 10A indicates that the contact can handle a maximum current of 10A at 250VAC ； 24VDC 2-5A indicates that at 24VDC, the maximum current that can be conducted or interrupted by this contact is 2 to 4A. It is best not to exceed this value during use.

So for contacts of 250VAC 10A or 24VDC 5A, can it work at 250VAC 5A? What about 24VDC 2A? Thank you

Yes, it hasn’t exceeded the contact capacity.

This post was last edited by HEJIYUER on 2015-6-7 at 10:53. The original poster need not worry; that contact capacity is related to the thermal effects of current, that is, active power. For example: 1. The contacts are connected to the control circuit of the lamp, which operates at 220VAC/600W; therefore, the load on the contacts does not exceed 5 amps, so it is suitable for use. 2. If it is used in the circuit of a 24VDC alarm indicator light, and the instantaneous current of that indicator light is 6 amps, then it cannot be used; instead, a relay contact with a rating of more than 6 amps for 24VDC should be used (there is no need to worry about the AC load current of the contacts, as this is a DC circuit). Select the contacts based on the voltage level and load power.

Thank you for your reply. Regarding the first point, I would like to ask again: the magnitude and direction of alternating current voltage change periodically. I want to know that, at the same power level, if the voltage decreases, could this lead to an increase in current, causing the current through the contacts to exceed 5A?

This depends on the characteristics of the load. For example, in the case of an air conditioner, it can operate at 198V as well; if the compressor is able to deliver its rated power at that voltage, then the current will increase – the current passing through your contacts will rise, and the VA power rating will increase slightly (even though the voltage is decreasing). As mentioned earlier, the contacts are used to measure active power, so the value will increase slightly as well. Because electrical equipment has a minimum starting voltage ； No matter what, the overload is only slightly more than the rated power ； Moreover, the equipment comes equipped with its own overload protection, so there’s no need for concern; the power rating of your contacts is also quite high. If a high load is encountered, then a \"power relay\" should be used, which is commonly employed in electrical engineering. The simplest way is to check the maximum current indicated on the nameplate of the device under load; this will not be wrong.