According to the Institute of Electrical and Electronics Engineers (IEEE), a relay is a device through which the contacts in one circuit get operated by changing the conditions of the same circuit or in multiple associated circuits.
Whereas contactors are devices that are used for recurrent establishment and interruption of an electrical circuit under standard conditions. However, understanding what makes contactors different from relays can be a bit more confusing when you consider their specifications and applications.
What Makes Relays Different from Electrical Contactors?
While the definitions of contactors and relays sound similar, there aren’t enough details to understand the difference between both properly. Contactors and relays both execute an identical task of turning or switching a circuit.
To help you understand how they both work and what differentiates the two devices, read below.
- Load Capacity
Mostly, relays are classified at a carrying load of 10A or less. In contrast, contactors are used for carrying loads that are greater than 10A. However, the actual difference lies in the physical configuration differences and industry standards.
- Open and Closed Contact Standards
Contactors are practically designed to function with Form A or usually open electric contacts. On the other hand, relays are typically designed for both Normally Open and/or Normally Closed conditions, which depend on the required function of the device. With contactors, when the device de-energizes, there usually is no connection, but with relays, there could still be a live connection.
- Spring-Loaded Contacts (Safety Components)
Due to the fact that contactors typically carry high loads, they often come in-built with supplementary safety elements such as spring-loaded contacts, which helps confirm that the circuit is broken when the device de-energizes.
In cases of high loads, contacts can fuse themselves and lead to dangerous implications. Thus contactors play a valuable role in the protection of electrical devices. For the same, spring-loaded contacts help reduce the chance of any unwarranted electrical incident and ensure that all circuits are cut-off simultaneously. However, relays are typically used for lower loads.
- Arc Suppression (Safety Functions)
Another safety element commonly included in contactors due to the high loads that they typically carry is an arc suppression. The function of arc suppression operates by extending the pathway an arc needs to travel.
In case the distance is stretched more than the energy can surmount, then the arc is suppressed. Whereas, relays are not designed and built for high loads, meaning that arcing is not an issue, which means arc suppression on relays is much less common.
- Overloads (Safety Features)
Contactors are generally connected to overloads, which interrupts the circuit in case the current surpasses a pre-defined threshold for a stipulated duration, such as 20-40 seconds. Thus, overloads help safeguard the equipment discharge of the contactor from any kind of damage due to surge or discharge in the current. Whereas, on relays, overloads are much less common.
How To Choose Between Contactors and Relays for Your Electrical Application?
Motor protection contactors and relays are crucial components of any electrical machinery system. Both these devices perform the critical task of protecting the motor from any damage, such as a burnout that is caused due to overload.
When choosing the best contactors and relays, you need to know the different conditions where the application of each device can be employed. You also have the option of buying added accessories for motor and load control management.
When selecting between contactors and relays, you can follow these general rules. Read below:
When to Use Relays:
- 10A or Lower current
- Circuit pressure of Up to 250VAC
- Delivery for 1 phase
When to Use Contactors:
- 9A or higher current
- Circuit pressure of up to 1000VAC
- Delivery for 1 or 3 phase
Moreover, it would help if you consider the aspect of functionality. For any circuit where there is a chance that an overload condition can occur and a failure to entirely de-energize the circuit may lead to unsafe conditions, contactors make for the best choice due to the extra safety features and elements.
However, before you make any decision about purchasing contactors or relays, you can always talk to a professional about your unique requirements to get the best recommendations.