Best Solid State Relays AI pick
Chosen by an AI model from its trained knowledge, with its reasoning.
AI pick: Crydom D2425
The Crydom D2425 is the reference panel-mount SSR for DC-controlled switching of 240 VAC resistive loads like heaters, with genuine published derating data.
Not for: DC loads, highly inductive or motor loads needing random turn-on, or installs without a proper heat sink.
AI picks by need
For compact DIN-rail with integrated heat sink
Carlo Gavazzi RGS (line)
The RGS series slim SSRs mount on DIN rail with heat sinks sized by the maker, which removes the thermal guesswork.
Not for: Retrofits into the standard hockey-puck panel footprint.
For PLC or PCB-level switching
Omron G3NA (line)
The Omron G3NA SSRs offer the standard footprint from a major control brand with clear specs.
Not for: Users needing three-phase switching in one unit.
What the AI looks for in Solid State Relays
- Heat sinking and derating
- Mount on a heat sink with thermal compound and derate per the maker's current-versus-ambient curve. Size the SSR well above the steady load current. SSRs dissipate heat continuously, and an unsunk SSR fails far below its label rating.
- AC or DC output
- Use triac or SCR output for AC loads and MOSFET output for DC loads. An AC SSR will not turn off a DC load.
- Zero-cross or random turn-on
- Use zero-cross for resistive heaters. Use random turn-on for phase-angle control and some inductive loads. The wrong switching mode causes inrush or prevents proportional control.
- Control input
- Confirm the input range matches your controller (for example 3-32 VDC for PLC or PID outputs, or an AC input). A DC-input SSR will not respond to an AC control signal, and an input outside its range may not trigger it.
- Off-state leakage and failure mode
- Expect leakage current when off, and expect SSRs to usually fail shorted. Add a disconnect or contactor upstream for safety. Leakage can keep small loads glowing, and a shorted SSR leaves a heater on.
Brands that matter
- Crydom (Sensata): Panel-mount and DIN SSRs with full thermal data.
- Carlo Gavazzi: RM, RGS and RGC ranges, many with integrated heat sinks.
- Omron: G3NA and G3PE industrial SSRs.
- Opto 22: Long-running industrial SSRs and I/O modules.
- Schneider Electric: Zelio SSR range.
What to avoid
- Unbranded clones of 'Fotek' SSRs, which are widely counterfeit with overstated current ratings.
- Running near the label amps without a heat sink.
- Using an SSR as the only isolation for maintenance.
Questions
Why does my lamp stay dimly lit when the SSR is off?
SSRs pass a small leakage current. Add a bleed resistor or use an electromechanical relay for very small loads.