SCR3L Three-Phase SCR Voltage Regulator: Signal Wiring, Sizing and Installation

The SCR3L is an integrated three-phase SCR power regulator for 380VAC resistive heating loads. Phase control, signal conditioning and regulation are combined in one module, so a single analog signal from a PID controller or PLC sets heating power across all three phases. Ordering data is on the SCR3L product page.

1. Specification

Parameter	Specification
Rated voltage	3-phase 380VAC, four-wire
Rated current	60A / 100A / 200A
Frequency	50Hz / 60Hz
Control signal	4–20mA, 0–10VDC, 1–5V, or 10kΩ / 2W potentiometer
Built-in power supply	AC220V — the neutral connection is required
Optional external power	DC12V ≥1A
Output voltage asymmetry	≤5%
Mounting size	92mm wide × 147.6mm high, Ø5.3mm fixing holes
Load	Three-phase resistive

2. Four-wire connection

The module derives its internal 220VAC supply between one phase and neutral, so the neutral conductor must be connected even when the heater itself is a three-wire delta load. A missing neutral is the most common installation fault: the display and signal stage appear dead while the power terminals are live.

• Connect L1, L2, L3 and N on the input side, and the three heater legs on the output side.
• Where no neutral is available at the panel, use the DC12V ≥1A external supply option instead.
• Provide upstream short-circuit protection sized for the module rating on all three phases.

3. Control signal selection

Parameter	Specification
4–20mA	Best choice for long cable runs and noisy plant. Pairs with a TC4 or TC5 controller ordered with current output.
0–10VDC / 1–5V	Common on PLC analog output cards; keep the cable short and screened.
10kΩ potentiometer	Manual power setting from a panel knob, with no controller in the loop.

Screen the signal cable, earth the screen at one end only, and never run it in the same trunking as the 380VAC load cabling.

4. Sizing

• Per-phase current for a balanced three-phase resistive load: I = P / (1.732 × 380).
• A 40 kW heater draws about 61 A per phase, so a 100A module is the correct choice — not the 60A.
• Allow additional margin for high ambient temperature inside the cabinet and for continuous duty.
• Phase-angle control draws non-sinusoidal current; check that upstream cabling and protection are rated accordingly.

5. Commissioning

• Verify phase rotation and that neutral is present before energising.
• With the heater isolated, apply the minimum control signal and confirm zero output, then ramp to maximum and confirm smooth increase.
• Measure output voltage on all three phases at mid-setting; asymmetry above 5% indicates a failed SCR leg or an unbalanced load.
• Check module and cabinet temperature after 30 minutes at full power and confirm ventilation is adequate.
• Record the control signal type in the panel documentation — the module cannot be identified visually as mA or V configured.

6. FAQ

Do I need the neutral wire?

Yes, unless you use the DC12V external supply option. The internal supply is taken between phase and neutral.

Can the SCR3L control a motor?

No. It is designed for three-phase resistive heating loads.

What is the difference from the BSTY series?

Both are three-phase regulators; the BSTY series adds soft-start and RS485 communication options. See the BSTY overview.

Which controller pairs with it?

Any PID temperature controller with a 4–20mA output, for example a TC4 or TC5 ordered with current output.

Sizing and quotations: sales@strong-ele.com.