About SSR:

A solid state relay (SSR) is an electronic switch, which, unlike an electromechanical relay, contains no moving parts. 

The types of SSR are photo-coupled SSR, transformer-coupled SSR, and hybrid SSR. 

A photo-coupled SSR is controlled by a low voltage signal which is isolated optically from the load.

The control signal in a photo-coupled SSR typically energizes an LED which activates a photo-sensitive diode. 

The diode turns on a back-to-back thyristor,silicon controlled rectifier, or MOSFET transistor to switch the load.

40A SSR

Features: 

-Reliable SMT technology 

-High ultra insulation resistance over 50M¦¸/500V DC 
-High dielectric over more than 2.5KV 
-Low enable current less than 7.5mA/12V DC, compatible with CMOS IC or TTL 
-Low EMI/EFI & surge by zero cross trigger method 
-High surge current over 410A/one cycle (60Hz) 
-High surge voltage duration by snubber circuit 

Specifications: 

-Load Voltage: 24-380VAC 

-Load Current: 40 A 

-Input Voltage: DC 3-32V 

Package content: 1pcs Solid state relay for temperature controller