A contactor is an electrical device that is widely used for switching circuits on and off. As such, electrical contactors form a subcategory of electromagnetic switches known as relays.
A relay is an electrically operated switching device that uses an electromagnetic coil to open and close a set of contacts This action results in a circuit powering either on or off establishing or interrupting the circuit). A contactor is a specific type of relay, although there are some important differences between a relay and a contactor.
Contactors are principally designed for use in applications where a large amount of current needs to be switched. If you are looking for a concise electrical contactor definition, you could say something like the following:
A contactor is an electrically controlled switching device, designed for repeatedly opening and closing a circuit, Contactors tend to be used for higher current-carrying applications than standard relays, which do a similar job with low current switching.
Download Catalog PDFAn electrical contactor is used in a wide range of situations where there is a need to switch power to a circuit repeatedly. Like relay switches, they are designed and built to perform this task over many thousands of cycles.
Contactors are mainly chosen for higher power applications than relays. This is because of their ability to allow low voltages and currents to switch. or power cycle, a far higher voltage/current circuit on and off.
Typically, a contactor will be used in situations where power loads need to be turned on and off frequently or rapidly. However, they can also be configured either to power on a circuit when activated (normally open, or NO contacts), or to shut down power to a circuit when activated (normally closed, or NC contacts).
The two classic applications for a contactor are as an electric motor starter – such as those that use auxiliary contacts and connectors for use in electrical vehicles - and in high-powered lighting control systems.
When a contactor is used as a magnetic starter for an electric motor, it will usually also provide a range of other safety features such as power-cutoff, short circuit protection, overload protection, and under-voltage protection.
Contactors being used to control high-power lighting installations will often be arranged in a latching configuration, to lower overall power consumption. This arrangement involves two electromagnetic coils working in tandem. One coil will close the circuit contacts when briefly energised and hold them closed magnetically. The second coil will open them again when powered. This sort of setup is especially common for the automation of large-scale office, commercial and industrial lighting setups. The principle is like how a latching relay works, although the latter is more often used in smaller circuits with reduced loads.
As contactors are intended specifically for these sorts of high voltage applications, they tend to be physically larger and more robust than standard relay switching devices. However, most electrical contactors are still designed to be easily portable and mountable and are generally considered highly suitable for use in the field.
Send Inquiry TodayThere are several reasons why an electrical contactor could suffer a failure and need repair or replacement. The most common is contact welding or contact sticking, where the contacts of the device become stuck or fused in one position.
This is typically a result of excessive inrush currents, unstable control voltages, too low transition times between high peak current simply due to normal wear and tear. The latter usually manifests as a gradual burning off of the alloys coating the contactterminals, causing the exposed copper underneath to weld together.
Another ess common reason for a failing contactor is coil burn, most often caused by an excessive or insufficient) voltage at either end of the electromagnetic col. Dirt, dust, or moisture ingress into the air gap around the coil can also be a contributing factor.
The main difference between an AC contactor and a DC contactor lies in their design and construction. AC contactors are optimized for AC voltage and current characteristics, while DC contactors are designed specifically for DC voltage and current. AC contactors are typically larger in size and have different internal components to handle the challenges of alternating current.
When selecting an AC contactor, you need to consider factors such as the voltage and current rating of your AC system, the power requirements of the load, the duty cycle, and any special application-specific requirements. It is recommended to consult the manufacturer’s specifications and consult with a qualified electrician or engineer for proper selection.
How Do Contactors Work？
To better understand how a contactor works, it is helpful to know about the three core components of any electrical contactors device when assembled. These are normally the coil, the contacts, and the device enclosure.
The coil, or electromagnet, is the key component of a contactor. Depending on how the device is set up, it will perform a specific action on the switch contacts (opening or closing them) when it receives power
The contacts are the components of the device that carry power across the circuit being switched. There are various types of contacts found in most contactors, including springs and power contacts. Each type performs a specific function in transferring current and voltage
The contactor enclosure is another important part of the device. This is the housing that surrounds the coil and contacts, helping to insulate the contactor’s key components. The enclosure protects users against accidentally touching any conductive parts of the switch, as well as offering robust protection against risks such as overheating, explosion, and environmental hazards like dirt and moisture ingress
The operating principle of an electrical contactor is straightforward. When the electromagnetic coil has a current passed through it a magnetic field is created. This causes the armature within the contactor to move in a certain way regarding the electrical contacts
Depending on how the specific device has been designed and the role it is intended for this will normally be to either open or close the contacts.
If the contactor is designed as normally open (NO), exciting the coil with voltage will push the contacts together, establish the circuit, and allow power to flow around the circuit, When the coil is de-energised, the contacts will be open, and the circuit will be off. This is how most contactors are designed
A normally closed (NC) contactor works the opposite way. The circuit is complete (contacts closed) while the contactor is de-enerqised but interrupted (contacts open) whenever current is supplied to the electromagnet, This is a less common configuration for contactors, although it is a relatively common alternative setup for standard relay switches
Contactors can rapidly perform this switching task, over many thousands (or indeed millions) of cycles during their full working lives.
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