Technical Guides · 2026-08-23
How to Wire TCN4S and TCN4H/L/M Temperature Controllers: Contactor and SSR Methods
Terminal-by-terminal wiring instructions for the TCN4S-14RV and TCN4H/L/M-14RV PID temperature controllers, covering AC contactor (relay output) wiring, BSSR-25DA solid-state relay wiring, K type and PT100/Cu50 sensor connections, SSR heat sink sizing and a commissioning checklist.
1. Which TCN4 model do you have?
The TCN4 series digital PID temperature controller is supplied in two terminal layouts. Both are wired the same way in principle, but the terminal numbers are different, so identify the model on the housing label before you start.
| Item | TCN4S-14RV | TCN4H / TCN4L / TCN4M-14RV |
|---|---|---|
| Terminal count | 12 terminals | 14 terminals |
| 220 VAC power | Terminals 1 and 2 | Terminals 1 and 2 |
| Relay output short link | Short 2 to 3 | Short 2 to 5 |
| Contactor coil A2 terminal | Terminal 4 | Terminal 6 |
| K type thermocouple (blue / red) | 9 (blue) / 10 (red) | 13 (blue) / 14 (red) |
| 3-wire PT100 / Cu50 red wire | Terminal 8 | Terminal 12 |
A clear wiring diagram is also printed on the side of the product for easy installation.
2. Safety notice
This controller provides both RELAY contact output and SSR drive output, but the two outputs cannot be used at the same time.
Isolate and lock off the supply before wiring. 220 VAC is present on the power and load terminals. Use an AC contactor with the relay output when the load power exceeds 1000 W. Wiring must be carried out by a qualified electrician in accordance with local regulations.
3. Method A — AC contactor (relay output)
RELAY output: use an AC contactor when load power exceeds 1000 W. The controller relay energises the contactor coil, and the contactor main contacts carry the heater current.
3.1 TCN4S-14RV with AC contactor
Controller: connect terminals 1 and 2 to 220 VAC; short terminal 2 to terminal 3; connect terminal 4 to contactor coil A2; connect coil A1 to neutral; connect contactor L2 to live and L3 to neutral; connect the load to T2/T3. Terminals 6 and 7 drive the alarm beacon.
3.2 TCN4H/L/M-14RV with AC contactor
Controller: connect terminals 1 and 2 to 220 VAC; short terminal 2 to terminal 5; connect terminal 6 to contactor coil A2; connect coil A1 to neutral; connect contactor L2 to live and L3 to neutral; connect the load to T2/T3. Terminals 8 and 9 drive the alarm beacon.
4. Method B — Solid-state relay (SSR drive output)
With the SSR drive output the controller switches a solid-state relay instead of a contactor. The diagrams below use the Strong Electric BSSR-25DA single-phase SSR, which accepts a 3–32 VDC control signal and switches a 24–380 VAC load.
4.1 TCN4S-14RV with BSSR-25DA solid-state relay
Controller: connect terminals 1 and 2 to 220 VAC; connect SSR terminal 2 to live; connect SSR terminal 1 to the load. Terminals 11 and 12 carry the DC control signal to the SSR, and terminals 6 and 7 drive the alarm beacon.
4.2 TCN4H/L/M-14RV with BSSR-25DA solid-state relay
Controller: connect terminals 1 and 2 to 220 VAC; connect SSR terminal 2 to live; connect SSR terminal 1 to the load. Terminals 3 and 4 carry the DC control signal to the SSR, and terminals 8 and 9 drive the alarm beacon.
5. Sensor wiring: K type, PT100 and Cu50
Both layouts accept a K type thermocouple or RTD probe. Observe the wire colours — reversed thermocouple polarity makes the reading fall while the process heats up.
- TCN4S-14RV, K type thermocouple: blue wire to terminal 9, red wire to terminal 10.
- TCN4H/L/M-14RV, K type thermocouple: blue wire to terminal 13, red wire to terminal 14.
- TCN4S-14RV, 3-wire PT100 / Cu50 RTD: red wire to terminal 8, the other two wires to terminals 9 and 10 in either order.
- TCN4H/L/M-14RV, 3-wire PT100 / Cu50 RTD: red wire to terminal 12, the other two wires to terminals 13 and 14 in either order.
6. Contactor or SSR: how to choose
| Criterion | AC contactor (relay output) | BSSR-25DA SSR (SSR output) |
|---|---|---|
| Switching frequency | Slow, seconds to minutes per cycle | Fast, suitable for continuous PID cycling |
| Wear parts | Mechanical contacts wear and pit | No moving parts |
| Temperature stability | Wider overshoot band | Tighter control around setpoint |
| Heat dissipation | Negligible | Heat sink required |
| Typical use | Loads above 1000 W with slow thermal response | Ovens, extruders, packaging machines, tight PID control |
7. SSR sizing and heat sink selection
Size the SSR at roughly twice the steady-state load current, then fit a matched SSR heat sink. A single-phase SSR dissipates about 1 to 1.5 W per ampere, so a 25 A load produces roughly 25 to 38 W of heat inside the panel.
- Apply a thin, even layer of thermal paste between the SSR base and the heat sink.
- Mount the heat sink with the fins vertical so convection air can rise freely.
- Add forced-air cooling above approximately 40 A of continuous load current.
- Keep the DC control wiring separated from the AC load wiring to avoid interference.
8. Commissioning checklist
- Only one output method is wired: either relay/contactor or SSR — never both.
- 220 VAC supply is connected to terminals 1 and 2.
- The relay short link is fitted: 2–3 on TCN4S-14RV, 2–5 on TCN4H/L/M-14RV.
- Contactor coil A1 goes to neutral; A2 goes to terminal 4 (TCN4S) or terminal 6 (TCN4H/L/M).
- SSR terminal 2 goes to live and SSR terminal 1 goes to the load.
- Thermocouple polarity is correct: blue and red on 9/10 (TCN4S) or 13/14 (TCN4H/L/M).
- The controller input type parameter matches the fitted sensor (K type, PT100 or Cu50).
- The output type parameter matches the wiring method actually used.
- SSR is mounted on a heat sink with thermal paste and unobstructed airflow.
- All terminal screws are torqued and the reading rises when the process heats up.
9. FAQ
10. Technical support
Beijing Strong Electric manufactures PID temperature controllers, solid state relays and SCR power modules and thermocouples and RTD sensors. More wiring and setup articles are collected in our Technical Guides.
- Email: sales@strong-ele.com
- Website: strong-ele.com