Unison 803 Slim Solid State Relay: More Heater Zones in Less Panel
When a panel has twenty heater zones, every millimetre of DIN rail counts.
The Unison 803 is a slim, 23.6 mm wide zero-cross SSR that mounts straight on a 35 mm DIN rail with its own heat sink. It switches the same heater loads as a 45 mm relay but lets you fit roughly twice as many channels in a row — ideal for extruders, hot-runner controllers and multi-zone ovens.
803 Specifications
| Parameter | Value |
|---|---|
| Width × height | 23.6 mm × 44 mm (relay module) |
| Mounting | 35 mm DIN rail with matched heat sink |
| Control input | 4–32 VDC, 4–16 mA, LED indication |
| Output (48 code) | 24–480 VAC, 47–63 Hz |
| Output (58 code) | 24–580 VAC, 47–63 Hz |
| Peak inverse voltage | 800 V (25/40 A) · 1400 V (50/90 A) |
| Isolation | 4 kV body · 6–8 kV input to output |
| Protection | Built-in snubber and TVS surge suppression |
| Switching | Zero-cross |
From the Unison 803 specification sheet.
How Much Current an 803 Carries
| 803 model | Heat sink | Continuous current at 40 °C |
|---|---|---|
| 25 A | V-87 | about 18 A |
| 40 A | V-87 / B-24 | about 20 A / 30 A |
| 50 A | B-72 | up to about 40 A |
| 90 A | B-72 | up to about 60 A |
Per Unison’s data at 40 °C panel air. Hotter panels need more margin or forced ventilation.
Why Panel Builders Choose the 803
Half the rail
Ten 45 mm relays need about 450 mm of rail; ten 803s need about 236 mm. That can save a whole panel size.
580 VAC headroom
The 58-code 803 has 1400 V peak inverse voltage, giving margin on 415 V lines with spikes from long cables and contactors.
Rail-mount service
Clip on, clip off. No drilling a back plate for each heat sink, and wiring stays in neat rows.
Unison 803 in Stock
Mounting Tips for Slim SSRs
- Keep them vertical. Fins must run up and down so hot air rises through them.
- Mind the neighbours. Slim relays mounted side by side heat each other; above about 60 % of rating, leave a gap or add a panel fan.
- Check panel air temperature. Ratings are at 40 °C. In a 50 °C panel, reduce current or move to the next heat sink size.
- Tighten terminals properly. Loose load terminals are the most common cause of burnt SSRs — re-torque after the first heat cycles.
- Choose 58-code on 415 V. Use the 580 V version on phase-to-phase 415 V loads for extra voltage margin.
Unison 803 Slim SSR FAQs
How wide is the Unison 803?
The relay is 23.6 mm wide, about half the width of a standard 45 mm SSR.
What is the difference between 803 ZDA 48 and 803 ZDA 58?
48 versions switch 24–480 VAC; 58 versions switch 24–580 VAC with a higher 1400 V peak inverse rating.
Does the 803 need a separate heat sink?
It mounts on a matched DIN-rail heat sink. The heat sink size decides the continuous current.
Can the 803 be driven by a temperature controller?
Yes. Any controller with an SSR drive (voltage pulse) output of 4–32 VDC can drive it directly.
Is the 803 suitable for motors?
It is a zero-cross relay intended for heaters and resistive loads. For motors, use a relay rated for inductive loads with generous current margin.
Do you stock the 50 A slim version?
Yes, the 803 ZDA 58 50 01 is in stock with same-day dispatch.
Plan a Slim SSR Panel
Send us the number of zones, heater power per zone, supply voltage and panel size. We will suggest the 803 model, heat sink and layout.
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