replacing start stop push switch with relay

A peek inside (picture of the inside) MIGHT help. Control voltages can be anything. In the US a 208/240 motor will likely have a step down transformer to 120 VAC, but HVAC systems use 24 VAC. Stuff operated by PLC's might even have 24 VDC.

In these START/STOP controls, the START button is NO - Normally open and would be in parallel and the STOP button is NC (Normally Closed) and would be in series. The voltages and the NO/NC status can be easily checked. Your relays (2 of them) may have to be a TIME DELAY (one shot relay).

Usually, motor starts are not that complicated.
 

MaxHeadRoom

Joined Jul 18, 2013
30,666
I
But all i want to say that i want replace only the start stop switch with two relay my relay coils will be driven by a circuit that i made,i want to connect the push buttons in the "no" pin off the relay so i want to know that what are the volt and amp ratings in the push button pins
Stop/Start P.B.s carry a trivial load when used to pick up a relay or contactor.
It is what ever the load current of the coil, usually no more than a couple of amps.
Max.
 

shortbus

Joined Sep 30, 2009
10,050
Stop/Start P.B.s carry a trivial load when used to pick up a relay or contactor.
It is what ever the load current of the coil, usually no more than a couple of amps.
Max.
Just rewired my metal cutting lathe, the 'control' circuit had a 2amp fuse in it, for pulling in 3 contactors.
 

PhilTilson

Joined Nov 29, 2009
154
As usual, half the 'helpful' responders have failed to understand the OP's requirement!

He has a motorised pump with a control panel with start and stop buttons on it. Clearly the motor is actually switched on and off via a contacter - a momentary start push-button wouldn't do it, would it?

He wants to start the pump remotely, therefore he wants to cause the contacter to pull in by means of a relay rather than a push button. As MaxHeadroom said earlier, the only requirement, therefore, is to switch the contacter coil current. Typical consumption for a contacter for a pump like that would be 5 - 10VA with an inrush of probably 10X that. So any relay with a contact rating in excess of about 1 amp should be fine.

It would be very foolish to do as some seemed to suggest, and run the motor directly through a 40A relay, or whatever. Motor start contacters have built in over-current protection, stall protection etc.
 

Thread Starter

Niladri Pal

Joined Jun 21, 2017
18
As usual, half the 'helpful' responders have failed to understand the OP's requirement!

He has a motorised pump with a control panel with start and stop buttons on it. Clearly the motor is actually switched on and off via a contacter - a momentary start push-button wouldn't do it, would it?

He wants to start the pump remotely, therefore he wants to cause the contacter to pull in by means of a relay rather than a push button. As MaxHeadroom said earlier, the only requirement, therefore, is to switch the contacter coil current. Typical consumption for a contacter for a pump like that would be 5 - 10VA with an inrush of probably 10X that. So any relay with a contact rating in excess of about 1 amp should be fine.

It would be very foolish to do as some seemed to suggest, and run the motor directly through a 40A relay, or whatever. Motor start contacters have built in over-current protection, stall protection etc.
Atlast someone finally solved it realy nice.thanks for you rply.i already soughted it out.thanks for your rply.
 
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