Solid State Relay Attributes & Their Applications (3-Phase)

A three phase SSR is essentially 3 individual single phase SSRs packaged in a single housing with a common input so that each SSR is energized simultaneously. In fact, it is not uncommon for engineers to use 3 individual SSRs to switch power to a three-phase load when a single three phase SSR is not suitable for one reason or another.

For three phase resistive heating applications, zero crossing three phase SSRs are commonly used. These versions will switch power to the load at the zero-voltage crossing point of each phase to minimize inrush currents. Random turn-on SSRs are recommended for switching inductive loads, such as motors, compressors, or transformers where it is desirable to switch 3 phases on at the same moment. All AC output SSRs (except special versions built with FETs or IGBTs) turn off at zero current irrespective of whether they are zero voltage or random turn-on SSRs and thus reduce transients otherwise caused by collapsing of a coils magnetic field found in electromagnetic relays.

SSR Main Attributes:

  • Contactless turn on and turn off (no arcing, contact bounce, or acoustic noise)
  • High speed switching
  • Long life expectancy
  • Low input control power requirements
  • No inductive feedback from a mechanical relay coil (no reverse-voltage back feeding into control circuit to cause damage)

See also:
Source -
DigiKey Solid State Relays (SSR)
DigiKey Expansion Boards, Daughter Cards
DigiKey Contactors (Solid State)
DigiKey I/O Relay Modules