Contactor Selection Guide for HVAC Systems

Contactor Selection For Heating, Ventilation and Air Conditioning
In heating, ventilation and air conditioning (HVAC) the most important of all the electrical components providing the safe operation of the motors, compressors and other machinery is the contactor. Correct contactor selection, for actuating, is essential to the satisfactory performance, economy and safe operation of the HVAC system. This guide is to help the HVAC technician in selecting contactors.
Contactor? What’s That?
A contactor is a switch, operated electrically, which controls motors, lights or other electrical machines. In an HVAC system the contactor controls the large currents which switch on and off the compressor, fans, pumps, etc. The contactor must be physically large enough to absorb the heavy inrush drawn in some HVAC§ motors.
Key Factors in Contact (contactor) Selection for HVAC Systems
Current Rating. Next in importance to the “down-the-line” specifics of contact impacts is the current rating, the all-around most important parameter in selecting a contactor. Selecting the wrong environment for the HVAC contactor and all else relating to the electrical system’s control is an expensive write-off. Select a contactor whose current rating is well in excess of any maximum current that the equipment to be controlled would require (the running current and inrush at startup).
Voltage Rating. Contactors are “rated” to receive the and deliver a voltage of given levels.HVAC Equipment would normally consist of Equipment for controlling 208V, 240V, 380V, 480V, etc.Pick a contactor that accepts and delivers the required voltage.Coil Voltage
This is the voltage that the coil is rated for operation at. It has to equal that of the control voltage that you will be using in your HVAC control circuit. Generally, you’ll have voltages of 24V, 110V 120V,240V, and 440V. Get it wrong, and you can kiss a bunch of good bucks goodbye.
Type of Contacts
The type of contacts is of some importance in a contactor. Usually these are of the normally open (NO) type used in an HVAC application. That is to say, the contacts are open when the contactor is deenergized, and closed when they are energized (same as saying it is open when deactivated), and the current can flow.
Pole Configuration
The number of poles that your contactor has can determine how many electrical circuits that you can control. A 3‐pole contactor will be adequate for most HVAC systems, since it is controlling three phase power to be utilized by motors. Some may call for an even 4‐pole type contactor, or maybe just a single‐pole type (depends on how your circuits are powered).Environmental Conditions
HVAC systems can be functionally challenged in operating in difficult environmental conditions of high temperatures, humidity, and dust or even corrosives.
Ingress Protection
Get the contactor of suitable ingress protection (IP) rating for the expected conditions of operation.
The higher the IP number, the more protected the contactor to dust and water ingress and therefore more suitable for environmental challenges.
In HVAC, contactors are frequently controlled by themostats or by a BMS. Make sure the contactor you go for will suit the mode of operation you plan to use, manual, automatic, or remote control.
Short Circuit Protection
The contactor you go for should have built-in protection to avoid short circuiting to not only save itself but the HVAC system too. Check for the thermal and/or magnetic overload protection, if needed, and also provide fuses or circuit breakers for the other electrical components.
Size and mounting type
Make sure the contactor you go for fits into the available space in the HVAC system. Some contactors are available in DIN rail or screw mounted types. A properly sized contactor that is easy to service in a particular layout is what you will need.
Longevity and Reliability
An HVAC should be expected to run for long periods of time in continuous service, therefore the contactor must be designed to last and go on suffering the “incessant attack” that on/off operation brings on.
Additional Considerations
Energy savings: Saving per watt, switching losses on contactor though small can add up.
Cost: With the foregoing parameters duly met, cost will also enter into the choice.
Manufacturer and warranty.
Summary
You can see that correct selection of a contactor will go far in helping your HVAC system perform in a satisfactory mode. The foregoing factors should help you to avoid the mistakes alluded to.
Last but not the least; No worse type of failure has occurred than that for which a particular component was not suited. Though not stemming from a catastrophic failure, it is not pleasant to have a contactor actually burn out on you when bad.