I'm just trying to introduce cold water in to industrial shredder. Connected cold water supply to machine. That's not good because when I forget to turn off water it will overflow. I have not seen whats inside machine, but I know there will be a PLC, contactors and +24V power supply.

I'm thinking to install NC solenoid valve 24 V DC and power it from auxiliary contacts on motor contactor. Therefore water will be introduced only when the motor is running. To be more specific, there is three L1, L2, L3 and NO auxiliary contact on top and bottom sides of contactor.

I am thinking to get +24 V DC from power supply which supplies power to PLC, connect it to NO auxiliary contact on contactor, another NO auxiliary contact goes to solenoid valve, then from solenoid valve goes to 0. 0 will be on terminal block somewhere. My concern is that scheme will be safe?

Machine operates outside, temperatures winter from -5 to summer +25. Water will go (solenoid activated) for about 15 sec, then stop for 15 sec, then start again x4 times. Solenoid will not burn? PLC will not burn? I'm thinking to install Asco Solenoid Valve SCE238D002.24/DC, 2 port , NC, 24 V DC, 1/2 in.

Any help would be appreciated.


1 Answer 1



simulate this circuit – Schematic created using CircuitLab

Figure 1. SW1 - 3 are the contactor contacts. SW4 is an auxiliary contact.

If the solenoid is adequately rated and the PSU has adequate spare capacity then your plan is fine. Make sure that there is no chance of accidental connection between the mains and DC circuits. Check the 24 V supply voltage with solenoid off and solenoid on. The PLC isn't switching the solenoid so it won't be at risk.

  • \$\begingroup\$ Thank you. Its been working more than year with no problems. Also I added flyback diode between solenoid positive and negative terminals \$\endgroup\$
    – bbarclays
    Commented May 10, 2020 at 22:52
  • \$\begingroup\$ That was nice of you to report back. Thanks. \$\endgroup\$
    – Transistor
    Commented May 10, 2020 at 22:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.