SMC-50 (150) soft starter fault codes: status LED, fault buffer, Shorted SCR, Line Loss, 7026 and fixes

An SMC-50 soft starter (Bulletin 150) shows a fault in two places: the multi-colour status LED below the HIM bezel (steady red = non-resettable fault, flashing red = resettable fault) and, when a 20-HIM-A6 or configuration software is connected, the word FAULTED with the fault code, a short description and the elapsed time (150-UM011F-EN-P, pp. 109, 199). A fault shuts the controller down; an alarm only warns of a pending fault (p. 109). The full code list is Table 129 (p. 204), the descriptions are in Table 130 (pp. 205–207) and the causes and fixes in Table 131, "Fault Display Explanation" (pp. 210–214).

Read the LED and the HIM first

Source: Table 125, p. 199.

• Port number in front of the code: when the fault comes from a device in a DPI port, the port number is shown first. Port 7, fault 26 is displayed as 7026 (p. 109).
• 150-SM6 module: one LED (>) shows the source, red for the controller and yellow for the motor, and the other three give a code from 0 to 7; one code covers several faults, so read the exact code on a HIM or in software (pp. 199–200).
• Codes 71 to 77 (Start, Slow Speed, Stop Option, Coast, Clear Fault, Fault, Param Change) are event codes, not faults (pp. 204, 213–214).
• "Starting" with no output: one or more phases missing, or an isolation contactor that does not pick up; the Aux relay controlling the isolation contactor must be set to "Normal" (p. 214).

Fault and alarm buffers

• Parameters 138 to 142 hold the last five fault codes and parameters 143 to 147 the last five alarm codes, newest first (p. 201).
• On the 20-HIM-A6, the DIAGNOSTIC folder lists the last five faults and the last 100 alarms; select one and press ENTER to see the date and time it occurred (p. 203).
• The same buffers are available in Connected Components Workbench software (p. 203).

Is the fault enabled?

Faults and alarms are switched on bit by bit: parameter 136 [Starter Fault En], 137 [Starter Alarm En], 230 [Motor Fault En] and 231 [Motor Alarm En] (p. 110). In parameter 230 every motor fault is disabled by default except Overload, Power Qual and Open Load (p. 111). So a jam, stall or underload will not trip the starter unless someone enabled its bit. Shorted SCR, SCR Overtemp, CT Loss, HAL ID, NVS Error, V24 Loss, VControl Loss, Power Pole PTC and I/O Config are always enabled (pp. 205–206).

Common fault codes

"x" is the port number of the expansion module (p. 214). Ground Fault and Motor PTC need the optional 150-SM2 module, and ground fault also needs an 825-CBCT sensor (pp. 206, 214).

Checks, step by step

1. Record before resetting: LED state, the code with its port number, parameters 138 to 147 and the time stamps in the DIAGNOSTIC folder.
2. Supply faults (1–3, 18–20, 52–54): line and load connections, fuses, the power system and the delay settings (pp. 210, 212). If Line Loss is disabled, the manual suggests enabling Undervoltage to limit motor damage from phase loss (p. 127).
3. Shorted SCR (4–6): disconnect main and control power, mark the wires and record the parameters, then measure line to load on each phase (L1-T1, L2-T2, L3-T3) with an ohmmeter. Above 5,000 Ω is good; otherwise replace the power assembly (p. 215). In a wye connection a single shorted SCR is not detected until the unit is started (p. 205).
4. Open Gate, CT Loss, HAL ID (7–9, 30–33): remove the control module from the power section and check that TB2 to TB7 are firmly seated, as Table 131 lists for each code (pp. 210–211).
5. Temperature (10, 60, x059): ventilation, duty cycle, fan, ambient. For Motor PTC, the 150-SM2 input responds at 3400 Ω ± 150 Ω and trips on a short circuit at 25 Ω ± 10 Ω (p. 254).
6. Load faults (21–24): overload class, service factor and Motor FLC against the nameplate, then the machine (pp. 205, 210). Parameter 188 [Stall Delay] runs after the ramp time, default 10.0 s (p. 119).
7. Control power (36, 37, 100…199): control voltage at terminals 1 and 2, grounding, RC snubbers (pp. 211, 214).

Clearing faults safely

Fix the cause first; a reset does not correct it (p. 201). Ways to clear a fault (p. 201):

• Press HOLD TO TEST, PUSH TO RESET for less than 2 seconds. Holding it 3 to 10 seconds creates Test Fault 62, and more than 10 seconds starts tuning mode (p. 199).
• A N.O. push button on Option Input #1 (terminal 11) or #2 (terminal 10), programmed for Clear Fault in parameter 56 [Input 1] or 57 [Input 2], or an input on a 150-SM4 module.
• Cycle control power. NVS Error is not cleared this way; it needs a parameter change or loading defaults (p. 206).
• Automatic restart, below.

An overload fault cannot be reset until parameter 18 [Motor Therm Usage] falls below parameter 80 [OL Reset Level] (p. 201), default 75 % (p. 114); parameter 20 [Time to OL Reset] shows the time left (p. 114).

Auto restart. Parameters 135 [Strtr Restart En] and 264 [Motor Restart En] enable automatic restart fault by fault; all bits are disabled by default. Parameter 133 [Restart Attempts] sets the number of tries and 134 [Restart Dly] the delay; for an overload the restart waits for parameter 18 to fall below parameter 80 (p. 133). Auto-restart can start the motor without warning; follow the plant's permit and lockout rules.

Hazardous voltage is present in the motor circuit even when the SMC-50 is off; disconnect main power before working on the controller, motor or control devices (pp. 7, 209). L1, L2, L3, T1, T2 and T3 carry hazardous voltage, and on internal bypass units T4, T5 and T6 as well (p. 7). Never test the controller with an insulation resistance tester; the test voltage can destroy the SCRs (pp. 8, 209).

When it is hardware

• Shorted SCR test below 5,000 Ω: replace the power assembly; spare parts are listed in publication 150-TD009 (p. 215).
• Open Gate after the resistance check, Open Bypass from an inoperable bypass: replace the power module (p. 210).
• CT Loss with a failed current feedback circuit: control module and/or power section (p. 211).
• HAL ID with an incompatible power section (p. 211).
• V24 Loss, VControl Loss, System Faults, a stuck Test button: replace the control module (pp. 211, 213–214).

A failed power switching component can single-phase the motor; the manual recommends an isolation contactor or shunt-trip breaker on the line side, and a function check after any short circuit (pp. 7–8).

Before calling for support

Note the catalog number, the firmware, the codes and time stamps in the buffers, and the parameter values. If the starter's own overload is disabled, external motor overload protection should be used (p. 214), and two-speed or multiple motors need separate overload relays (p. 98); if that relay is an E300, see E300 trip and warning codes. Need an engineer on site: breakdown support.