SSR and switch control contactor

[JackPW]

hopefully a dumb question. I'm doing a retrofit where a 120v switch is controlling a starter contactor. I'm adding PLC that uses a SSR (triac) to operate the starter. is there any reason i can't leave the pushbutton wiring the way it is and just attach the SSR to the contactor?
Wondering if having voltage on the output of the SSR when it's off will cause any issues. the SSR is protected with TVS diode.
Thanks

 

[thingstodo]

hopefully a dumb question. I'm doing a retrofit where a 120v switch is controlling a starter contactor. I'm adding PLC that uses a SSR (triac) to operate the starter. is there any reason i can't leave the pushbutton wiring the way it is and just attach the SSR to the contactor?
Wondering if having voltage on the output of the SSR when it's off will cause any issues. the SSR is protected with TVS diode.
Thanks

We use Rockwell rack-based IO to do exactly that. 1756-IA16 inputs, 1756-OA16I outputs. No problems with voltage on the output if it is not turned on.



Read the specs on our SSRs and put in a breaker or a fuse after your output and before your contactor. When the starter gets weak (and it eventually will) it will start to draw more current. If there is no protection on your outputs, you can kill your SSR. We get a couple starters a year fail this way.



Just so you remember - SSRs 'leak' a bit of current. I don't remember how much, but enough to show voltage when you are checking with a meter. You need a load connected to 'drag down' the voltage.

 

[James Mcquade]

the only dumb question is the one not asked.

in regards to triac and ssr outputs is that with no load on them, they are turned on due to the nature of the electronics. when a specified load is placed on them, that forces the outputs to escentialy turn off.

so to sum it up.
an scr or triac output will show power to the output even when the output is turned off when there is no load on the circuit.

an scr or triac output will show no power to the output when the output is turned off when there is minimal load on the circuit.

AND HERE IS THE TRICKY PART
an scr or triac output will turn on when the load connected to the output is removed, thereby creating an electrical hazard.
CARE must be taken to document on the control panel that these devices are used and make sure that all maintenance personnel are trained on triac and scr devices. this is ESPECIALLY true for hazardous areas in which arc detectors are used in fire sprinkler systems. ours could see a spark from over 100 yards and dump 110 gallons per minute from each sprinkler
james

 

[JackPW]

Thanks for the replies.
I wasn't sure if damage or shortened life would occur since the manual switch would supply full voltage to the output of the SSR when the SSR was supposed to be off.