ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Semiconductors as contactors

I have loved to use these during the last 25-30 years, and always owersized the ampacity, so did I here to. It was labeled 25A and the max load on the circuit was 9 amp. for several hours.
Nothing else than this and 2 cm of the cables was ruined, but now I will use a contactor (rated 25A) 🙂 More noice more power to energize and hopefully more safe. 🙂

Maybe not only for non US Electrical systems, but this is in Norway at 230V 50Hz

We have had SSRs for at least 40 years but I am not sure how many were making their way into general industrial use. The good ones came from ISO22 or Crydom. They usually died a quiet death, just not passing current. These white Asian SSRs seem to fail more catastrophically. I have had several blow up. I am not sure whether the SSR blew the motor cap or it was the other way but the SSRs have failed in a similar manner in other applications including resistance heaters.



These things do not qualify as a "disconnect". They are just used for circuit control.

It was working for quite long, ususally not more than 3 hours continiously, but when it got longer time with constant load the cooling was not good enough, I should prbably had a thermostatic protection... Now I have a contactor the old fashined way, time will show how it works out....

I suspect the triac or an internal connection just went bad. I have had horrible luck with these Asian SSRs. The old ones we used seldom failed and when they did it was quiet, No melting, smoke or fire. The check sorters I worked on in a previous life had about 50 of them in each machine. Everything from 2a to 45a rated. The 2a failed a lot (small shaded pole motor) until they swapped them all for 10a units but it was a quiet failure. I am using them in my spa controller for an 11kw heater (two 5.5kw elements) and the pumps.

Crydom, Gavazzi, celduc, omron are serious brands for those.
Also Siemens make them in a slim version with integrated heat sink and din rail mount, very handy.

Hi Guys,
Are these devices being used to switch unity (resistive) power factor loads or inductive/capacitive loads?
One thing I do know is that SSR's do NOT like back-EMF from inductive or capacitive currents, unless you install some sort of a snubber circuit with a couple of reverse connected diodes in parallel with the load and the input.
Reason I say this, is because we recently had a power inverter system supplying a horrendously inductive plant (all motors with no PF correction), this burned out 7 SSR's.
Before you install anything in a plant or installation, do your homework on what power factor you are walking into, it could be so terrible that what your new work could make things worse.
Huge currents from un-corrected power factors have also killed electricians in the past, thinking that a given circuit only supplies so many amps.
Just be aware of this.

Some of the loads we had in the sorters needed snubbers (RC networks) but strangely the bigger 3p motors didn't. We were still losing 2a SSRs on a small shaded pole motor (fraction of an amp) and the answer after a while was to use a 10a unit. The 3/4 HP 208 3p motors were on 40a or later 45a devices. We lost an SSR occasionally but it was pretty rare.