Proper Installation of AC Contactors | A Practical Guide to Avoid Burning and Misoperation, Master It in One Article

AC contactors are widely used for switching and controlling power circuits. They use main contacts to open and close circuits, and auxiliary contacts to execute control commands. Main contacts typically only have normally open contacts, while auxiliary contacts often have two pairs of contacts with normally open and normally closed functions. Small-sized contactors are also frequently used as intermediate relays to work with main circuits, thereby achieving the function of remote control or controlling high-voltage electricity via low-voltage electricity.

The contacts of an AC contactor are made of silver-tungsten alloy, which has excellent electrical conductivity and resistance to high-temperature ablation.

AC contactors are further divided into permanent magnet AC contactors and electromagnetic AC contactors.

The operating power of an electromagnetic AC contactor comes from an AC electromagnet. The electromagnet is formed by laminating two "mountain"-shaped thin silicon steel sheets; one is fixed, with a coil wound around it, and there are multiple options for the operating voltage. To stabilize the magnetic force, a short-circuit ring is added to the attracting surface of the iron core. When the AC contactor loses power, it resets by means of a spring. The other part is a movable iron core, which has the same structure as the fixed iron core and is used to drive the opening and closing of the main contacts and auxiliary contacts.

Permanent magnet contactors are a new type of low-power contactor that replaces the traditional electromagnetic drive mechanism with a permanent magnet drive mechanism.

Its working principle is based on the principle that like magnetic poles repel and opposite magnetic poles attract. Since the polarity of the permanent magnet installed on the contactor's linkage mechanism is fixed, the soft iron fixed on the contactor's base, together with the electronic module solidified with it, generates a positive and negative pulse current of ten to twenty milliseconds under the action of an external control signal. This causes the soft iron to generate different polarities, thereby enabling the main contacts of the contactor to achieve the purposes of closing, holding, and releasing.

The main advantages of permanent magnet contactors are as follows:

• Good operational reliability, without any interference from grid voltage.

• Fast action speed, ranging from 0.12s to 0.15s (compared to 0.35s to 0.38s for traditional ones).

• Quiet operation, no AC noise, and not affected by dust or oil stains.

• No temperature rise in the module, good aging resistance, and a service life three times that of traditional contactors.

• Maintenance-free and super energy-saving protection.

Contactors with a current rating of 20A or above are equipped with arc-extinguishing covers, which use the electromagnetic force generated when the circuit is opened to quickly break the arc, thereby protecting the contacts.

AC contactors are manufactured as an integrated unit, and their appearance and performance are constantly improving, but their function remains unchanged. No matter how advanced technology becomes, AC contactors still hold an important position.

Contactors are divided into AC contactors (voltage: AC) and DC contactors (voltage: DC), and they are used in power, power distribution, and electricity consumption scenarios. In a broad sense, a contactor refers to an electrical device in industrial electricity that uses the magnetic field generated by current flowing through a coil to close the contacts, thereby controlling the load.

Before installing an AC contactor, it is essential to understand the issues that need attention during installation and use; only by doing so can subsequent work proceed smoothly. The most important issues are the normal operating conditions and installation conditions of the AC contactor.

Normal Operating Conditions and Installation Conditions of AC Contactors

• Ambient air temperature: -5℃ ~ +40℃. The average value within 24 hours shall not exceed +35℃.

• Altitude: Not exceeding 2000m.

• Atmospheric conditions: When the maximum temperature is +40℃, the relative humidity of the air shall not exceed 50%; at lower temperatures, higher relative humidity is allowed (e.g., 90% at 20℃). Special measures shall be taken for condensation occasionally caused by temperature changes.

• Pollution degree: Level 3.

• Installation category: Category Ⅲ.

• Installation conditions: The inclination between the installation surface and the vertical plane shall not exceed ±5°.

• Shock and vibration: The product shall be installed and used in a place without significant shaking, impact, or vibration.

AC Contactor Model and Specification Table

There are many different models of AC contactors. In practical applications, different models of AC contactors have different parameter values, and the working conditions they can withstand and the scope they can adapt to are also different. Therefore, only by understanding and being familiar with the main models and technical parameters of contactors can we select, install, and maintain them reasonably and correctly according to the requirements of electrical equipment in practical applications. Therefore, the editor has prepared an AC contactor model and specification table for everyone; let’s take a look!

Main Specifications of AC Contactors

• Classified by current rating: 115A, 150A, 185A, 225A, 265A, 330A, 400A, 500A, 630A, 800A.

• Classified by the rated control power supply voltage (Us) of the contactor coil:

• AC: 50Hz or 60Hz, including AC110V (115V), AC220V (230V), AC380V (400V);DC: DC110V, DC220V.