150-C37NBR — SMC-3 Soft Starter, 37A, 200–480V AC, with Internal Bypass

The 150-C37NBR is a 37A soft starter from the SMC-3 series, designed for three-phase induction motors up to about 18 kW at 480V AC. It controls the voltage applied during starting to reduce inrush current and limit mechanical shock on the drive train — belts, couplings, and pump impellers all benefit from not taking a full-voltage torque hit on every start. The internal bypass contactor closes once the motor reaches full speed, routing load current around the SCR power stage and eliminating the heat that non-bypass units generate continuously at full load.

At 37A, this soft starter covers a useful mid-range of industrial loads: 10–18 kW pumps, fans, compressors, and conveyor drives that run for extended periods after starting. The bypass contactor matters at this current rating — without it, the SCRs in a non-bypass unit would dissipate meaningful heat at 37A continuous, adding to the panel thermal load and degrading semiconductor service life over time.

Specifications

Parameter	Value
Part Number	150-C37NBR
Series	SMC-3
Rated Current	37 A
Input Voltage	200–480V AC, Three-Phase
Control Voltage	100–240V AC (separate terminals)
Motor Power (approx. @ 480V)	~18 kW / 25 HP
Starting Mode	Voltage ramp (soft start)
Soft Stop	Yes (programmable)
Internal Bypass Contactor	Yes
Start Ramp Time	1–30 seconds (potentiometer adjustable)
Initial Torque	Adjustable (front-panel potentiometer)
Fault Relay Output	1 × Form A
Device Protection	Phase loss, overtemperature (SCR thermal)
Enclosure	IP20 / Open Type
Operating Temperature	−10°C to 40°C
Standards	IEC 60947-4-2, UL 508, CE

Sizing — What "37A" Actually Means for Your Application

The 37A rating applies to normal duty starting — a standard centrifugal load accelerating within the default ramp time at standard ambient temperature. Several conditions reduce the effective rating:

High ambient temperature: rated at 40°C maximum. Above this, output current must be derated. A hot panel interior on a summer day can easily exceed 40°C — if this is likely, derate or consider the next larger unit.
Extended ramp times: longer start ramps (above 15 seconds) keep the SCRs conducting for longer during each start, increasing thermal stress. For heavy-inertia loads that require 20–30 second ramps, check the thermal derating curves for the 37A unit at the specific ramp time and duty cycle.
Frequent starts: more than 4–5 starts per hour generates cumulative SCR heat that must dissipate between cycles. Check the duty cycle rating for the expected start frequency.
Motor service factor above 1.0: if the motor runs continuously above its nameplate current (using its service factor), size the soft starter for the actual running current, not the motor nameplate FLA alone.

FAQ

Q: What is the difference between the 150-C37NBR and the same part without the "R" suffix?

The "R" indicates an internal bypass relay/contactor is included. A non-R version runs full load current through the SCRs continuously, generating more heat. The bypass version is the preferred choice for motors that run for extended periods after starting.

Q: Does the soft starter protect the motor against overload?

No. The SMC-3 protects the soft starter's own SCRs from overtemperature and monitors for phase loss. Motor overload protection requires a separate overload relay or electronic motor protection relay in the circuit.

Q: Can the ramp time and initial torque be adjusted without software?

Yes. Both are set via potentiometers on the front face of the unit — no programming tools needed. Adjust, run a test start, observe the acceleration profile, and fine-tune.

Q: Can this unit handle a star-delta motor?

The SMC-3 is designed for in-line (series) connection. Star-delta motors can be connected with the motor terminals in their delta configuration and the soft starter in series — but verify the motor's terminal configuration and the wiring arrangement against the soft starter installation instructions before proceeding.

Q: What is the soft stop function used for?

Soft stop ramps down the motor voltage gradually instead of cutting power abruptly. This is primarily used for centrifugal pumps to prevent water hammer and pressure surge in the discharge piping when the motor stops. For fans and conveyors, soft stop reduces mechanical jerk on the drive train.

150-C37NBR New Bulletin 150 Smart Motor Controller 150C37NBR