AC CONTACTORS USING DC VOLTS

[frink12]

WHAT WOULD HAPPEN TO A 120 VOLT AC 5 AMP CONTACTOR IF 120 VOLT DC 5 AMP WAS USED? ALSO WHAT WOULD HAPPEN IF THE CONTACTOR WAS DC AND AC WAS APPLIED?

 

[Ed MacLaren]

Re: AC CONTACTORS USING DC VOLTS

WHAT WOULD HAPPEN TO A 120 VOLT AC 5 AMP CONTACTOR IF 120 VOLT DC 5 AMP WAS USED?

I assume you mean the coil. It would not draw 5 amps. With no inductive reactance to limit current flow, it would draw 5 to 10 times normal current and produce smoke.

ALSO WHAT WOULD HAPPEN IF THE CONTACTOR WAS DC AND AC WAS APPLIED?

Pull-in current would be less than normal, it would "chatter" and would not pull in reliably. If it was not able to pull in, the coil might overheat and burn up.

Ed

 

[jim dungar]

Re: AC CONTACTORS USING DC VOLTS

If you are concerned with the power contacts, the answer is:

There should be no problem with closing on and carrying the DC voltage and current. however, breaking the load may be difficult if not impossible. The air gap of the open contacts may not be suffcient enough to break the DC arc.

You would need to confirm the DC ratings with the manufacturer. Many DC ratings are not published in general catalogs but they are available from the manufacturer. UL has only recently begun testing general purpose contactors for DC applications, but they have tested relay (power and control) contacts for years.