Non-Reversing vs. Reversing Contactor

Hello wjwlitespeed

I list the explanation below, for 3-phase squirrel-cage rotor motors.

DC and single-phase forward/reverse contactor systems all have the mechanical/electrical interlock so that only one contactor switches supply power to the motor at any time.

The wiring diagrams for special motors can be extremely complex.

A non-reversing contactor is just a single contactor, with three main switching terminals (1 per phase for a 3-phase supply to the motor.)

A reversing contactor is an assembly of two of the above, with a mechanical and electrical interlock between them, so only one contactor can be closed (giving power supply to the motor) at any time. The Forward/Reverse - Up/Down - Left-right etc. are usually opposite motions, and the opposite motions are obtained via labelled switching buttons which energizes the coil of the correct contactor, mechanically locking the other motion contactor and also electrically preventing it from closing.

In the standard 3-phase squirrel-cage rotor motor, the reverse motion is easily obtained by swapping any two of the 3 phase wires to the motor, which then runs in the opposite direction = reverse.

The schematic (Wiring diagram) of a reversing 3-phase contactor assembly is above.

A 3-phase standard non-reversing contactor wiring diagram is shown below, and has been called "Relay".

The contactor control voltages may be mains voltage or a special Control Voltage, often 24V DC is used as a standard Voltage for control systems in industrial switchboards.

I trust that assists you.

Should you need more information, reply here with

Kind Regards....

Dear sparkstation,

Excellently you explained.Very useful to all

my doubt is:

1) For a given rating of Induction motor,How to decide the rating of contactor and fuses? Please explain and give any thumb rule or formulae or any design data if available.

Kind regards

gova

gova1467,

Ratings are specified by each contactor manufacturer and fusing is specific to local installation codes in your area. Please consult with local suppliers for training on that subject.

Thanks a bunch Sparkstation. That's just what the doctor ordered.

wjwlitespeed

Dear Sparkstation,

can you plz give me an explanation on those 53 and 54 numbers regarding the both contactors? what kind of contacts are those, and what is their purpose? (maybe to "hold" the state of contact induced by the pushbuttons?). i seem not to be able to find those types of contacts on contactors i plan to use.

another thing: is there a possibillity of making an reversing contactor assembly without the mechanical interlock between the two (just electrical)?

Iggy

Basically, a reversing contactor is used to reverse the rotation of a motor. A non-reversing contactor just turns the motor on and off.

A reversing contactor interchanges two poles on a THREE PHASE (typically motor) application, such that the output ( the " T " terminals) are 120 degrees opposed from the input ( the " L " terminals). This is useful in a conveyor, for example. A three phase motor

that ran clockwise, normally, would run counterclockwise, when controlled via reversing contactor.

Provide HP and voltage, and frequency of motor and I can tell you the appropriate conductor,fuse,contactor, and thermal overload sizes for the USA.

Include service factor data from motor data plate,and the ambient temperature of both the motor location and the contactor location.

Do not know if these will be acceptable in your area or not, but it may be a good starting point.

A non-reversing DC contactor is a SPST relay that makes a circuit when a coil is energized. When it makes contact, it is dedicated to only one direction of flow. A reversing DC contactor will make contact on electricty flowing in both directions when the coil is energized because it is DPDT. The contactors are completely different from one another. If you want a picture of what they look like, go to http://www.newkellycontroller.com