Contactor Vs. Relay – How Does a Lighting Contactor Work?

By William K. Arner •  Updated: 09/10/21 •  7 min read

The contactor is an electromechanical switch used in an electrical circuit and plays the role of a power controlling device. A contactor is a multi-pole switch that means you can manage multiple electric devices at once. So, you can control several circuits with a single contactor, whereas one typical switch can only control one circuit. From light load to most complex machine, contactors are capable of handling.

Before jumping into how does a lighting contactor works, there are some basics you need to know. The contactors are considered as a particular type of relays because both have the same primary function. You can also say that the contactors are the better version of the relays. Let’s move on to the next section to known what differentiates a contactor from a relay.

Contactor Vs. Relays

Contactor Vs. Relay

The contactors and relays work in the same way, and both are electromagnetic switches. The electromagnetic switch’s specialty is that you don’t have to push anything to turn the switch on. By sending an electrical signal, you can turn the switch on.

Both relay and contactor are used to control multiple circuits or multiple loads at the same time. On the inside, both have a coil of wire. When current flows through, the coil engages an electromagnet and makes the contacts open or close. The contacts play the role of carrying the current flow.

Up to now, the discussion was all about similarities. Let’s focus on the differences between contactors and relays. According to size, relays are smaller than contractors. The relays can’t handle higher current, thus making them only useful for low voltage applications. In contrast, the contactors are bigger sized and suitable for higher voltage applications.

The relays are rated at a maximum of 15 amps that means they can carry loads of 15 amps or less. If it comes to carrying loads greater than 15 amps, a contactor takes the seat. The contactors are typically rated 50 amps or below, but you can also find higher-rated contactors.

You cannot change the coils inside the relays. So, this isn’t possible if you want to upgrade a relay to carry higher loads than its rated load. But, upgrading contractors are possible. In most contactors, you can replace the lower volt coil with your required higher volt coil.

Almost every relays have a normally open and normally closed option that will allow you to turn something on while turning others off. Where you cannot do the same in contactors. General use contactors stay either normally open or normally closed.

There are some contactors used for controlling light and called lighting contactors. By adding auxiliary contacts in lighting contactors, you can make them behave like relays.

How Do Lighting Contactors work?

For industrial applications, lighting contactors are used to control power to large lighting installations. For general use, like controlling lights in your house, lighting contactors will be overkill. House lighting is considered as a small consumer load, where lighting contactors are ideal for larger loads.

 As we now know what a lighting contactor is, let’s find out how this thing works. A lighting contactor can be either normally open or normally closed contactors. Every contactor has a coil of wire inside. If you dissect a lighting contactor, you will find two iron cores sitting on top and bottom of the coil. One coil is fixed in its position, and the other one is moveable. Both iron cores keep a distance from one another with the help of springs between them.

When you send an electric signal or current through the coil, it acts like a magnet to attract iron cores together. For normally closed contactors, the top iron core is attached with a plate that connects one terminal to another. After energizing the coil, the iron core attached to the plate goes down, opening all the terminals at once. Now, normally open contactors are just the opposite. When you energize the coil, instead of opening the terminals, the iron cores make all terminals closed.

For connecting circuits, every lighting contactor has contacts or also called poles. How many circuits you can connect to a contactor depends on how many poles it has. The poles can vary from one lighting contactor to another.

Depending on how you can control a lighting contactor, there are two types – electrically held and mechanically held. In electrically held contactors, sending electricity through the coil will make the contacts of a contactor either open or close. When you stop sending electricity, the contacts will go back to their normal state.

For mechanically held contactors, you also have to send electricity through the coil to make contacts open or close. But the difference is after you stop sending electricity, the contacts will stay in the same state as before. This situation of a contactor is identified as – the contactor is latched. This situation only occurs to mechanically held contactors is the reason they are also called latched contactors. There are two terminals, one for latching and the other for unlatching. So, to unlatch the contactors, you will need to send electricity or a signal through the unlatch terminal.

Some Facts About Lighting Contactors

Some lighting contactors are electrically held, and some are mechanically held, but there are lighting contactors that offer to be used as both. These specific lighting contactors come with a conversion unit. Running the electricity through the conversion unit will make the contactors mechanically held.  Running the electricity without the conversion unit will make electrically held contactors.

In lighting contactors, you can attach a unique feature called auxiliaries. By linking auxiliaries, you can add some extra poles with extra functionality. The auxiliaries have both normally open and normally closed options. So, if you have a normally closed contactor where all poles are normally closed, you can wire an auxiliary that will stay normally open and vice versa.

You can ask why differentiating poles by saying normally open or normally closed and why we even need these. So, both have importance in their way. Normally open means the circuit will stay open until you energize the coil, and normally closed is the opposite. Some applications require normally open contacts or poles, where some require normally closed contacts.

Normally open contacts are typically used as electrical motor starters, cooling circuits, ON push buttons, and lighting control circuits. On the other hand, normally closed contacts are used as stop pushbuttons, emergency buttons, limit switches, and motor protection circuits.

One thing you should be aware of is the coil voltage of your lighting contactor. Running higher voltage than the coil voltage will make the coil fry. Again, in a lower voltage, the contactors will stay idle. The same thing goes for the contacts or poles also. Running higher amps than the rated amps for contacts will damage the contacts eventually. But you can run lower amps than the rated amps.

There is an advantage of the coil over the contacts. That is, you can change the coil or replace them. But you cannot do so with contacts. If the contacts are damaged, the contactor will be useless, and you have to buy a new contactor.

Conclusion

At first glance, you might think the lighting contactors are very complex but trust me; they aren’t. When you finally get to know contactors, you will find it interesting more and more. In the above sections, you will get a thorough idea of how does a lighting contactor works and why they are so unique in their way. Some interesting but essential facts about lighting contactors are also included.

With that being said, I am signing off for now. Happy researching with lighting contactors!

William K. Arner

William K. Arner is an expert on lighting & indoor gardening. He has 12 years of research experience in lighting products and indoor gardening. William likes to collect different types of lighting & gardening products like grow lights, indoor-outdoor lights or automotive lights, and test them in different ways. He likes to write his experience as tips and reviews about lighting related products so that people can choose the best and perfect one for them.