Industrial AC solid state relays · Current rating versus ambient temperature, heat sinking, zero-cross or random switching, surge, leakage, dv/dt and control input
A solid state relay (SSR) switches an AC or DC load with semiconductors instead of moving contacts, isolated from its control input by an optocoupler, and is used to switch heaters, lamps and other loads. Fix three things before ordering: the load current the relay must carry at your enclosure temperature and how it will be cooled, the switching mode the load needs (zero-cross or random), and the load voltage, control signal and protection.
Panel-mount and DIN-rail SSRs for industrial AC and DC loads, single- and three-phase, with or without integrated heat sinks. PCB photo-MOS relays and optocoupler ICs, SCR phase-angle power controllers and electromechanical relays are outside this page; power relays and SCR power controllers have their own pages.
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01
Greegoo's datasheet for its 15–60 A DIN-rail SSRs with integrated heat sinks shows thermal derating curves against ambient temperature: the 15 A model holds 15 A to about 35 °C and falls to about 7 A at 80 °C; the 40 A model holds 40 A to 30 °C and falls to 20 A at 80 °C; and the 60 A model holds 60 A to 40 °C and falls to 30 A at 80 °C. [1]
The same datasheet lists an ambient operating range of −30 to 80 °C, maximum on-state voltage drop of 1.5 V (1.6 V for 60 A), a pure copper/alumina baseplate and a weight of 280 g, and warns that the side panels may be hot. [1] A Chinese SSR maker lists three ways to cool an SSR — aluminium heat sink, fan cooling and water cooling — and says it offers more than 50 heat sinks. [2]
Editorial calculation: reading the 40 A curve as a straight line from 40 A at 30 °C to 20 A at 80 °C, the relay can carry about 32 A in a 50 °C cabinet (40 − 0.4 × 20). With the 1.5 V maximum drop, 30 A of load current dissipates up to about 45 W in the relay (1.5 V × 30 A), which the heat sink and enclosure must remove. [1]
Editorial note: derating curves belong to a specific relay and heat-sink combination. If you mount a panel SSR on your own heat sink, ask the supplier for the curve for that heat sink's thermal resistance.
Give the supplier the load type (resistive heater, lamp, motor, transformer), load voltage and current, number of phases, switching frequency, enclosure ambient temperature and cooling, control signal (DC, AC or 4–20 mA), mounting (panel or DIN rail), protection (fuse, varistor), approvals and quantity.
02
Greegoo's datasheet offers zero-crossing or random (instantaneous) switching for resistive or inductive loads, with load voltage ranges of 24–480 V and 24–600 V AC (transient overvoltage 800 and 1,200 V peak) at 47–63 Hz. Turn-on is within ½ cycle for zero-cross and 1 ms for random-on models. [1]
The same datasheet gives 10 ms surge current ratings of 150, 250, 400 and 600 A for the 15, 25, 40 and 60 A models; minimum off-state dv/dt of 200 V/µs (500 V/µs for 60 A); off-state leakage up to 8 mA; and dielectric strength of 2,500 V rms input to output and to base. Its control inputs are 4–32 V DC (turn-on at 4 V, turn-off at 1 V, 10–20 mA) or 90–280 V AC (turn-on at 90 V, turn-off at 10 V). [1]
Another maker says it offers analogue-control SSRs for single- and three-phase loads with 4–20 mA, 1–5 V DC, 2–10 V DC or potentiometer input, as well as AC-controlled AC SSRs. [2] A further supplier divides SSRs into AC and DC output types and normally open or normally closed forms. [3]
Editorial note: the off-state leakage means a load is never fully isolated by an SSR; up to 8 mA can flow through a de-energized load, so isolate with a disconnect for maintenance and check that small loads or indicator lamps do not glow. [1]
A small modular SSR shows the low-current end. Finder's 77 Series data sheet (IX-2026) lists the 17.5 mm wide 77.01 in zero-crossing and random switch-on versions with a 1 NO output rated 5 A at 230 V AC (48–265 V switching range), a 300 A peak for 10 ms, an 800 V repetitive peak off-state voltage, a minimum switching current of 100 mA, off-state leakage of 0.5 mA or 3.5 mA (typ.) at 230 V depending on version, about 4 W of power loss at 5 A, an electrical life of 10 million cycles, 5 kV (1.2/50 µs) impulse insulation between input and output, −20 to +70 °C ambient and IP20. [4] Its lamp ratings show inrush limits: 1,000 W of incandescent or halogen but 800 W or 400 W of 230 V LED lamps depending on version. [4] Editorial calculation: the 100 mA minimum switching current means a load below about 23 W at 230 V may not switch reliably, and the 10 ms peak of 60 times rated current compares with 10 times (150 A on 15 A) for the larger relays above. [4] [1]
03
The listings reviewed range from panel-mount single-phase SSRs to heat-sink-integrated, three-phase, DC and analogue-control models; ask each for derating curves, surge and I²t data and the heat sink assumed.
04
The baseplate and heat sink decide the usable current as much as the output semiconductor does, because together they set the derating curve. [1]
| Part | Role | Fix in the order |
|---|---|---|
| Input circuit | Control voltage or current range. [1] [2] | DC, AC or analogue. |
| Optical isolation | Input-to-output dielectric strength. [1] [3] | Test voltage. |
| Output semiconductor | Load voltage, surge, dv/dt, drop. [1] | Ratings. |
| Zero-cross circuit | Zero-cross or random turn-on. [1] | Mode. |
| Baseplate and heat sink | Removes on-state loss; sets derating. [1] [2] | Heat sink; cooling. |
| Housing and terminals | Mounting and touch safety. [1] | Panel or DIN rail. |
05
Ask for the load current at your cabinet temperature rather than the nominal rating; Greegoo's 40 A model is down to 20 A at 80 °C. [1]
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Load Voltage (V AC) | 24–480 or 24–600 V AC; 800/1,200 V peak transient. [1] | Range; transient rating. |
| Load Current (A) | 15–60 A nominal, derated with ambient; 5 A modular with 100 mA minimum. [1] [4] | Current at your ambient. |
| Control Voltage (V DC or V AC) | 4–32 V DC or 90–280 V AC. [1] | Range; turn-on and turn-off. |
| Control Current (mA) | 10–20 mA (DC input). [1] | Range. |
| On-State Voltage Drop (V) | Max 1.5–1.6 V. [1] | Max drop. |
| Leakage Current (mA) | Up to 8 mA off-state; 0.5–3.5 mA (typ.) on a 5 A modular relay. [1] [4] | Max leakage. |
| Switching Time (ms) | ½ cycle zero-cross; 1 ms random-on; 10 ms off (AC input). [1] | Times. |
| Dielectric Strength (V AC) | 2,500 V rms input–output. [1] | Test voltage. |
| Insulation Resistance (Ω) | 10⁹ Ω at 500 V DC. [1] | Value. |
| Operating Temperature (°C) | −30 to 80 with derating. [1] | Range; curve. |
| Storage Temperature (°C) | −30 to 100. [1] | Range. |
| IP Rating | Touch-safe covers on DIN-rail models [1]; IP20 on the 5 A modular relay. [4] | Rating. |
| Weight (g) | 280 g with integrated heat sink. [1] | Weight. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Load: [type; voltage; current; phases] Switching: [zero-cross or random; cycles per minute] Ambient: [cabinet temperature; cooling] Control: [DC; AC; 4–20 mA] Mounting: [panel; DIN rail; heat sink] Protection: [fuse I²t; varistor] Approvals: [required marks] Quantity: [per model]
Greegoo publishes a DIN-rail SSR datasheet with derating curves; Jiangsu GOLD lists modular, heat-sink-integrated, DC and analogue-control SSRs; Xiamen Maxwell and Beijing Strong Electric list SSRs alongside temperature controllers; HONGFA, CNC Electric, Andeli and Naidian list them within their relay ranges.
Publishes a datasheet for 15–60 A DIN-rail SSRs with integrated heat sinks, zero-cross or random switching and thermal derating curves.
Product scope checked 2026-10-11
Lists single- and three-phase modular, heat-sink-integrated and DC SSRs, analogue-control SSRs and heat sinks.
Product scope checked 2026-10-11
Lists solid state relays in its relay range.
Product scope checked 2026-10-11
Lists single-phase and three-phase solid state relays alongside temperature controllers.
Product scope checked 2026-10-11
Lists SSRs and SCR power modules alongside temperature controllers.
Product scope checked 2026-10-11
Lists solid state relays, including a 30 A resistive-load model, in its relay range.
Product scope checked 2026-10-11
Lists single-phase solid state relays in its relay and contactor range.
Product scope checked 2026-10-11
Lists DC-to-AC solid state relays and describes AC and DC output types.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Greegoo's curve for its 40 A DIN-rail model falls from 40 A at 30 °C to 20 A at 80 °C ambient. [1]
Greegoo's zero-cross models turn on within ½ cycle; its random-on models turn on within 1 ms. [1]
Greegoo's datasheet lists off-state leakage up to 8 mA. [1]
One SSR maker lists aluminium heat sinks, fan cooling and water cooling. [2]
Yes: one 5 A modular SSR lists a minimum switching current of 100 mA, about 23 W at 230 V by editorial calculation, plus 0.5–3.5 mA (typ.) off-state leakage. [4]
Sources checked 2026-10-12. Greegoo publishes a DIN-rail SSR datasheet with ratings and derating curves; GOLD publishes SSR cooling and control options; Naidian describes SSR types; all three are also linked suppliers.
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