Industrial Electrical Troubleshooting
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Industrial Electrical Troubleshooting Advice
Industrial electrical maintenance troubleshooting means tracing a fault from its symptoms to its cause. This guide covers field diagnostics, electric motor testing, motor controller checks, and PLC inputs and outputs.
Industrial troubleshooting and electrical troubleshooting also require excellent computer skills. A laptop computer with PLC programming, communication, and operating programs is necessary for today's modern plant. Engineers, production supervisors, maintenance supervisors, maintenance technicians, electricians, instrument technicians, and maintenance mechanics must have PLC and computer knowledge, training, and troubleshooting skills. More about PLCs towards the end of this article.
As industrial troubleshooting relies on strong technical and analytical abilities, developing these skills can significantly support career growth. Mastery of PLC systems, diagnostics, and electrical problem-solving can open doors to broader job opportunities for electricians, including overseas roles, where professionals can further advance their expertise, gain exposure to diverse industrial systems, and build a more competitive skill set.
Basic troubleshooting techniques apply to every situation and occupation. Identifying the problem(s) is essential to solving the issues. The inexperienced troubleshooter often mistakes one or more of the symptoms for the problems. Solving the symptom(s) will typically postpone the problems to a later date. By this time, the issues may have grown to mountainous proportions.
An example is when a person experiences a headache and takes a mild pain reliever, such as aspirin. The problem might be any number of things: eyes need to be checked, medication or lack of medication, muscle strain, stress, tumor, blood vessel blockage, or old war injury. The same thing occurs in the industry; a fuse in a circuit blows, and the maintenance person gets the replacement fuse and inserts it into the fuse holder. Depending on the complexity of the circuit, many things could have caused the fuse to blow.
The excess current caused the fuse to open (blow). The excess current could have been caused by overload on the load, short circuit between the wires, grounded wires, short circuit in the load, ground in the load, voltage spike, voltage droop, etc. If the maintenance person does not troubleshoot the circuit before replacing the fuse and restoring power, negative consequences could arise.
It is not uncommon for a process to develop several small problems and continue to function at a degraded level of operational capability. Then, one more small problem occurs, and the whole process breaks down. Finding and correcting the last problem will not necessarily restore the operational capability of the process. The process continued operations with minor issues, but the small problems may not allow the process to restart from a dead stop. All the other minor issues must be identified and corrected before the process is restored to full operational capability.
This situation arises in the industry as well as a person. The person can continue to function with several minor problems, such as fatigue, blood pressure problems, hardening of the arteries, and artery blockage. Still, one more small blood clot in the wrong place could easily cause the death of the person. Clearing the blood clot does no good to the person. They will not be restored to full operational capability.
Field Electrical Troubleshooting
Unless prior experience dictates otherwise, always begin at the beginning.
Ask questions of the Operator of the faulty equipment:
- Was equipment running when the problem occurred?
- Does the Operator know what caused the problem, and if so, what, in their opinion, caused the problem?
- Is the equipment out of sequence?
- Check to ensure there is power.
- Before restarting, determine why the equipment stopped or the protective device tripped. Restore power only after the fault is corrected and the equipment is safe to operate.
- Use a voltmeter to check the following at the incoming and load side of circuit breaker(s) and/or fuses, ensure that voltages are normal on all legs, and read voltage to ground from each leg.
- Verify supply voltage against the equipment nameplate and drawings. Phase-to-ground voltage depends on the supply configuration; do not assume a universal value.
- Check AC control power against the transformer rating and circuit drawings. Distinguish line-to-line, line-to-neutral, and line-to-ground readings.
- Check low-voltage AC or DC control power against the power-supply rating. Verify polarity and grounding from the drawings; not all DC systems have a grounded negative conductor.
TIP: Add this Electrical Motor Troubleshooting chart link to your favorites so you can call upon your smartphone to guide you during electrical motor troubleshooting.
Check controlling sensors in the problem area, then make a complete check of all sensors, limit switches, and other switches to ensure they are in the correct position, have power, are programmed, set, and are functioning correctly.
If and when a problem is found, whether electrical or mechanical, the situation should be corrected, and the fault-finding began anew; a seemingly unrelated fault or defect could cause the problem.
When there is more than one fault, the troubleshooting is exponentially more difficult. Refrain from assuming all problems are solved after completing one; always test the circuit and operation before returning the equipment to service.
If available, check wiring diagrams and PLC programs to isolate problems.
For a variable frequency drive (VFD), record the fault code and follow the manufacturer’s diagnostic and reset procedure. A blank display does not verify that the DC bus is discharged. Observe the specified discharge time and verify the required safe condition before working on the drive.
Check that the wiring is complete and that wires and connections are tight, with no copper strands crossing from one terminal to another or the ground.
Ensure the neutral reading is good and the neutral is complete and not open.
Electric Motor Testing in the Shop
Before connecting a motor:
- Move motor to electric shop motor test and repair station.
- Connect motor leads according to the nameplate, available test supply, and manufacturer’s wiring diagram. Use correctly rated terminals and insulation.
- Measure winding resistance between A–B, B–C, and A–C using an instrument suitable for the expected resistance. Compare readings with manufacturer specifications and previous results; a fixed one- or two-ohm tolerance is not appropriate for every motor.
- Test insulation resistance using the test voltage and acceptance criteria specified for the motor. Disconnect drives and sensitive electronics before testing, account for temperature and moisture, and discharge the winding after the test according to the instrument instructions.
- Connect the motor to power test leads and safety ground after checking that test lead power is shut off; secure the motor to the table to prevent the motor from jumping when started; turn disconnect on; press the start button; check "T" leads for motor amperage; check for abnormal sounds and heat in bearings or windings; keep personnel clear of the rotating shaft; shut down and disconnect.
Electric Motor Testing in the Field
When a motor overload or circuit breaker trips and/or blows fuses, certain procedures and tests should be carried out:
- Isolate all energy sources, apply lockout/tagout, and verify absence of voltage before testing;
- Disconnect the motor circuit from drives and sensitive electronics, then test insulation resistance between each motor lead and ground using the manufacturer’s test voltage and criteria. Discharge the circuit after testing as instructed.
- With the circuit isolated and verified deenergized, compare phase-to-phase winding resistance with the manufacturer’s criteria. Separate the cable and motor at the disconnect to determine which part of the circuit contains the fault.
- With power isolated and absence of voltage verified, disconnect both ends of the conductors and test each conductor for continuity, conductor-to-conductor faults, and faults to ground using suitable test equipment;
- Inspect the cable run for the cause and extent of damage. Replace damaged conductors or the cable assembly as required, and correct the condition that caused the fault before restoring service.
- If the problem is on the motor side of the disconnect switch, open the motor connection box and disconnect the motor;
- Evaluate motor insulation resistance against the manufacturer’s criteria, test conditions, and historical readings. A single universal resistance threshold does not establish that every motor must be replaced;
- Compare phase-to-phase winding resistance with manufacturer specifications. Investigate open windings or significant imbalance before deciding whether repair or replacement is appropriate.
- If motor test readings are good, test the motor leads between the disconnect switch and the motor connection box for continuity and ground resistance. If readings are not good, replace wires;
- If electrical readings are acceptable, investigate mechanical loading, chains or belts, bearings, the gearbox, and supply disturbances. Reconnect and return to service only after the cause is addressed and the facility’s lockout/tagout removal and restart procedure is completed.
Motor Controller
- Check the motor Full Load Amps (FLA) at the motor and check the setting on the controller overload (OL) device; most newer OL devices are adjustable between specific ranges, and some older OL devices use heaters for a given amperage.
- If circuit disconnecting means in the controller is a circuit breaker, it should be sized correctly.
- Verify Motor Circuit Protector (MCP) selection and instantaneous-trip settings using the manufacturer’s instructions and applicable electrical requirements. Do not apply one fixed multiplier to every motor or protective device.
- Fuses protecting the motor should be the dual element or current limiting type based on the motor FLA.
PLC Training Prerequisites
On-the-job training on PLCs is usually only effective once the person being trained has reached a certain level of expertise in several areas. Knowledge and skills in electricity, troubleshooting, and computer operation are necessary prerequisites to assimilate basic PLC training effectively. In his experience, the author found that long-term retention of material studied was higher from a vocational course at a local junior college than from a fast-paced, cram course through a manufacturer.
The manufacturer's course covered essentially the same material as a course at the junior college (JC). The significant differences were the amount of study time and shop time. The JC course was four hours of class time per week for 15 weeks. There were three hours of shop time doing hands-on work on the problems and material covered in the first hour. Additional time was spent at home studying the manual and writing programs. Also, the JC was open at night for extra shop time on the PLCs and computers.
In contrast, the manufacturer's course was five, eight-hour days. Class work was extremely fast and condensed to cover the amount of material involved. The instructor was very knowledgeable and covered the course material as we tried to input the programs into desktop training equipment to see how they worked. By the end of each day, our minds were jammed with information. By the end of the week, we all passed the course, but I had difficulty remembering what we had studied on the first day.
Programmable Logic Controller (PLC) Troubleshooting
- Verify PLC supply voltage against the controller and power-supply specifications.
- Verify field-device supply voltage against the circuit drawings.
- Identify problem areas.
- Check sensor operation in the problem area.
- Check sensor Inputs to PLC.
- Check on PLC that a change in sensor state causes the corresponding Input LED on the PLC to go on or off.
- Identify Output controlled by Input on the PLC ladder diagram.
- Trace the program logic: the output should operate when the conditions preceding the output on the rung are true, subject to controller status and instruction behavior. An input change does not always command an output change.
- Check that the output voltage matches the module rating and the commanded output state.
- Locate the output device and verify that the commanded output voltage reaches it.
- Ensure that the Output device works correctly (solenoid, relay, contactor, etc.).
- An Input or Output module can be defective in one area or circuit and work correctly in all other circuits.
- If each field circuit is not fuse-protected, the modular internal circuit becomes a fuse and can be destroyed by a field short circuit or any other over-current condition.
- Check the modular circuit; if it is bad, the module must be replaced after correcting the field fault.
- Follow the manufacturer’s module replacement procedure and the facility’s energy-control requirements. Isolate the required controller and field supplies before removing modules.
- Locate fault in field circuit by disconnecting wires at module and field device. Check between wires for short circuits and to ground for short circuits; replace wire if a short circuit is found.
- Check the device for ground, short circuits, and mechanical and electrical operation. Always check the device for other faults, even when a problem is found in the wires. Problems in wires can cause a problem in the device or vice versa. If the device is defective, replace it and check the total circuit before placing it in operation. After restoring the circuit, check again to ensure the circuit and module are operating correctly.
- Check the power supply module; if there is no output, shut down the power and replace the supply module.
- If only some modules have power, inspect the supply, module connections, and backplane according to the manufacturer’s diagnostic procedure before replacing components.
- Record controller faults and machine status before a reset or power cycle. Follow the controller and machine manufacturer’s recovery procedure; key-switch positions and reset behavior vary by model.
- A latched bit may retain its state through a power cycle. Examine the latch/unlatch logic and documented restart sequence instead of assuming power cycling will clear it. Do not bypass safety interlocks.
- Possession and use of an up-to-date ladder diagram, elementary wiring diagram, manufacturer's manuals and diagrams, troubleshooting skills, operator's knowledge, and time are all required to solve issues in maintaining a modern manufacturing production line.
Industrial Electrical Troubleshooting FAQ
What is the first step in industrial electrical troubleshooting?
Identify the symptoms and ask the operator what happened before the fault. Review the equipment drawings and fault history, then follow the required electrical safe-work and energy-control procedures before testing.
What should be checked when a motor trips an overload?
Investigate mechanical loading, bearings, the driven equipment, supply conditions, wiring, and motor condition. Compare overload settings with the motor nameplate and protective-device instructions before returning the motor to service.
Does a PLC input always turn an output on?
No. The output depends on the program logic, controller status, and instruction behavior. Trace the conditions preceding the output on the rung and compare the commanded state with the output module and field device.
Is one insulation-resistance limit suitable for every motor?
No. Use the motor manufacturer’s test voltage and acceptance criteria, account for test conditions, and compare with historical readings. Disconnect sensitive electronics before insulation testing.
For additional controller diagnostics, see our PLC Troubleshooting Guide and PLC programming lessons. Access to the PLCLogix 500 or PLCLogix 5000 training simulator is required to complete the hands-on lesson series.
About the Author (original biography): Larry Bush has been an electrician for 47 years and in maintenance management for 22 years. Download his eBooks "Maintenance Policy and Procedures Manual" or "Emergency Diesel Electric Generators eBook"!
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