Solid state relay usage and ratings

Thread Starter

meowsoft

Joined Feb 27, 2021
494
It is safe for solid state relay to use for ATS then mechanical contactor ?, and it is need's derating for single phase motor load ?
 

Reloadron

Joined Jan 15, 2015
6,137
Yes, it's OK to use a SSTS (Solid State Transfer Switch) to switch a ATS (Automatic Transfer Switch) which is mechanical. If the ATS is driving a motor load it should be rated for the load stall current. That assumes your ATS is an automatic transfer switch. While I see no need for it yes, it can be done that way. Most motor starters are rated by the motor horsepower and come in single and poly phase designs including thermal overload protection. They also come in open frame and enclosed versions. You choose based on your specific application.

Ron
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Yes, it's OK to use a SSTS (Solid State Transfer Switch) to switch a ATS (Automatic Transfer Switch) which is mechanical. If the ATS is driving a motor load it should be rated for the load stall current. That assumes your ATS is an automatic transfer switch. While I see no need for it yes, it can be done that way. Most motor starters are rated by the motor horsepower and come in single and poly phase designs including thermal overload protection. They also come in open frame and enclosed versions. You choose based on your specific application.

Ron
No... It's safe for use solid state relay alone, without mechanical contactor ?, for client with 100a 1 phase, they want cheap transfer switch... and solid state relay is cheap here, even 3 phase 100a is available in market, and solid state relay is controlled by PLC, also PLC is powered by battery and battery is charged automatically, 12v 10ah battery
I was try before in my home but solid state relay is burnt, even with only 80% used rating, and everything is ok with only 50% used, 200a solid state relay in 100a sub panel, in my experiments
How to use solid state relay safely for stand alone automatic transfer switch ?, is there any guide ?
 

Reloadron

Joined Jan 15, 2015
6,137
I can share this much. If this was my situation in an industrial setting I would be going with a NEMA approved motor starter enclosure and a mechanical magnetic motor starter. Yes, a single phase 100 Amp (they are normally rated in motor horsepower) is a heavy load and if I were doing it I would use a magnetic mechanical motor starter with overload protection. Will a triac solid state circuit work? I am not sure since you are working into an inductive load you will need a snubber (RC Circuit) across your solid state switch. Also keep in mind a motor locked rotor current and a motor start current can be ten times the normal run current. Just also keep in mind over current protection. Hopefully another member may have some better suggestions involving the solid state process. Personally I just would not be comfortable with it unless of course you are looking at a soft start circuit but a full voltage across the line start circuit I am going with a mechanical magnetic motor starter for the motor's rated horsepower and including overload protection. If you go the solid state route just keep in mind a RC snubber.

Ron
 
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