A control contactor is a specific type of electromagnetic relay designed to manage large electrical loads. It is essential when the load to be controlled exceeds the power that the controlling element can handle, such as resistors, motors, or other high-power receivers. Contactors function similarly to switches: they establish or interrupt the reception of an electrical signal. The key difference between a contactor and a relay is that contactors are more robust, capable of withstanding significantly more current than relays (up to 10-12 amps).
What is the role of a contactor?
You may need a contactor to automatically control electrical equipment such as washing machines, radiators, dishwashers, hot water tanks, and similar appliances.
Note: While contactors are not essential components in your electrical installation, incorporating them offers significant benefits.
What does a contactor consist of?
A contactor consists of various components:
- A coil
- A phase shift ring
- A return spring
- Auxiliary contacts (open or closed)
- A magnetic circuit (comprising a moving part and a fixed part of the electromagnet)
How does a contactor work?
Your contactor is installed in your electrical panel. It can be manually operated through three separate controls:
- Automatic start
- Off
- Forced on
The contactor coil is powered by either alternating current or direct current (ranging from 5 to 500 V).
When the coil is energized, it generates a magnetic field: the moving part of the armature is attracted to the fixed part, causing the contacts to close (or open, depending on the model). When the coil is de-energized, the return spring separates the two parts of the armature, keeping the power contacts either open or closed. This mechanism enables your electricity provider to control the activation of your electrical appliances if you have subscribed to a peak/off-peak hours contract.
Various contactor models exist, with or without integrated auxiliary contacts that are open or closed. It's entirely possible to add auxiliary blocks to these contactors, which serve exclusively for remote control or signaling purposes.
Two terminologies are used for contacts. You may encounter NO, NC, NF, F, O.
NO (normally open) contacts are open when your contactor is not powered. When you energize your contactor, the contact closes, which is why they can also be referred to as NC (normally closed).
Conversely, NC (normally closed) means the contact is closed when unpowered. In English, NC corresponds to an NO (normally open) contact when energized.
This terminology applies to both main contacts (which power the controlled device) and auxiliary contacts (which provide feedback on the contactor's operation).
What are the main criteria for choosing a contactor?
Here is a list of criteria to consider when selecting the appropriate contactor for your installation:
- Need for manual control (water heater contactor or "off-peak" contactor)
- Control voltage of the contactor coil
- Supply voltage of the receiver
- Current rating of the receiver
- Number of power contacts (1, 2, 3, 4)
- Type of power contact:
> There are several designations for contact types
- Normally open NO or also called normally closed N/C
- Normally closed NC or also called normally open N/O
