Searching for a Furnas Contactor? What to Look For

Furnas contactors are used widely in the industry. You find contactors used in air conditioning, heating, refrigeration, food processing and agricultural units.

A contactor is an electrical device that controls a switch to a power circuit. It is like an electrical relay, except that it has significantly higher current ratings. Contactors make or break an electric circuit.

There are other differences between relays and contactors. Contactors usually come spring loaded, offer arc-suppression and often lack de-energized connections i.e. NC contacts. The contactor acts as a control switch that operates a circuit at a much higher power level.

Siemens acquired the Furnas company and its brand in 1996. The current products offered by Siemens-Furnas can replace most products previously manufactured under the Furnas name.

Companies use Furnas contactors as magnetic starters in many different industries, as lighting control for large buildings, and even as vacuum contactors in AC systems.


The Right Application

Although this advice applies to all electrical equipment, it is especially important when buying contactors. Contactors tend to be durable and do not experience extreme wear and tear during normal operations.

If you hear complaints about contactors wearing out frequently and requiring replacement, likely the appliance, motor or whatever has the wrong contactor in place.

Therefore, when you are choosing a Furnas contactor, make sure you understand what application it will be used for and ensure that whatever you purchase has the correct ratings for the application.

For a start, check between the two common standards, NEMA and IEC. The NEMA choice often gives you a much wider range of contactor options.

However, if you go by IEC standards, the contactors must be must closer to the rated values. Hence, basing your choice on IEC standards helps you to determine the most reliable and appropriate contactor for the job at hand.

Rating Characteristics

Regardless of which standard you choose, you need to know and understand some of the basic rating characteristics for contactors.

For example, one of the most widespread application of contactors is for motors. Therefore you also must consider the motor characteristics before determining the best contactor for your purpose.

The number of phases, poles, voltage and amp ratings, and the maximum and minimum voltage of the coils are all important characteristics. For many Furnas contactors, you can also find an NEMA rating (for example 00).

NEMA contactor ratings tell you how much current at a rated voltage the contactor can switch. The NEMA size also indicates the maximum continuous current rating and a rating for induction motors that may be attached to the contactor.

Furnas contactors range from 20 to 650 amperes with newer models offering an even wider range.

Magnetic Furnas contactors are very popular and have many uses in different applications. Some of the out-of-production contactor parts are still used in many industries today and eventually require replacement. Ratings may differ from the newer models, so when you are replacing an old magnetic Furnas contactor purchase the correct version.

Checking for Misuse and Depreciation

If you need to replace a Furnas contactor, you will buy a refurbished or used contactor. Along with a quality test and possible guarantee, you should perform a quick check to see if any signs exist of misapplication or wear and tear.

If the contactor has been operating with too much current, the contacts will overheat. The shape and look of the contact surface drastically change as the contacts overheat longer. Contacts can also heat up if they open too frequently or if they are unable to close quick enough. A simple inspection at the contact surface can show the signs of electrical deterioration such as severe pitting, melting, deformation or signs of abnormal physical wear and tear.

Overheated contactors cause the insulation to degrade quickly, which can result in short out or cause the contactor to fail.


Contactors often last for many years, so if you find yourself replacing a contactor after only a few years use, you might want to look deeper into the type of contactor you have and the use. If your previous contactor has failed, try to determine the exact cause before replacing it with an identical contactor. Misapplication, extended heated operations and other atypical conditions can accelerate the failure rate of electrical contactors.

Finally, do a quick check of your contactors by measuring the resistance of the coils. If the resistance varies significantly from a standard or new Furnas contactor, you may need to replace it.