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DC Contactor FAQ's



Q: What is the Mechanical Life Expectancy of a contactor?
A: Trombetta's contactors are rated for Electrical life only. Mechanical life expectancy is always greater than electrical life. Electrical life ratings determine the useful life of the contactor.


Q: What is the worst type of load to switch?
A: Inductive (motor) Loads First, Capacitive Loads Second, Resistive (light bulb) Loads are the most forgiving loads to switch.


Q: Why do you offer 2 types of contact material?
A: Generally speaking, copper is cost competitive and is good for switching loads but can have corrosion issues when used with resistive loads (i.e. no inrush). Silver is more expensive, however it resists corrosion and is good for low and high current switching.


Q: In a Static Power System, why do we need to size the coil voltage above the nominal rating, i.e. 24VDC/48VDC?
A: In a normal Static Power System, we need to take into account the "maximum battery equalization charge voltage" whereby if the nominal system DC voltage is at 24VDC, the maximum coil voltage will be around 30VDC. If the system nominal voltage is at 48VDC then we would size the maximum coil voltage at 60VDC. The reason for this is to alleviate any potential for premature coil thermal runaway. If using the product in a charging system please contact Trombetta.


Q: What is the maximum carry current rating of the Trombetta DC contactor product line?
A: Bear - 225 to 300 amps, Metals - 125 to 300 amps, Plastic - 100-200 amps, HP Plastic - 200 amps, PowerSeal - 150 amps, RP - 75 to 125 amps and Defender - 200 amps.


Q: What is the In-Rush current rating of the Trombetta DC contactor product line?
A: Bear - 600 amps, Metals - 500 to 700 amps, Plastic - 300 to 500 amps, HP Plastic - 600 amps, PowerSeal - 800 amps, RP - 150 amps and Defender - 400 amps.


Q: What are Magnetic Blowouts?
A: Rare Earth Magnets molded into the top cover which produce magnetic fields which act on the main contact arcing, thereby extinguishing the arc outwards. This is particularly true in the case of "Inductive Loads".


Q: Are the high current contacts polarity sensitive?
A: The contactors without blow out magnets can have any polarity on the high current contacts. Types with blow out magnets need to be wired up with the higher potential at the terminal marked with a + sign on the top cover. This is necessary to ensure that the blow out magnets push the arc out of the contactor.


Q: How do you install a DC contactor?
A: Please refer to the instruction sheet for the specific product. The instruction sheets can be found under each product section and on the literature page.


Q: What is the torque rating for mounting hardware on the studs?
A: The torque ratings are listed on the product label.


Q: How do you determine if a contactor is operating correctly?
A: One way is to determine if the Nominal Coil Resistance is at the right level.
1. From our literature on the web site (products/contactors) determine the Nominal Coil Resistance.
2. Get an OHMS meter that reads to mili Ohms (small ohms meter)
3. Connect the 2 leads to the 2 small studs/spades (To get an accurate reading, the contactor needs to be at room temperature and not recently energized).