How to Troubleshoot 3-Phase Power Systems in Older Commercial Buildings

Introduction

Troubleshooting electrical issues in older commercial buildings with 3-phase power systems can be challenging. However, with some background knowledge of how these systems work, a systematic approach, and the right tools, any technician can efficiently track down problems and restore power. In this article, I will provide an in-depth guide on troubleshooting 3-phase power in older commercial buildings.

How 3-Phase Power Systems Work

To troubleshoot 3-phase systems effectively, you need to understand some basics of how they operate.

• 3-phase systems use three hot wires, each carrying alternating current 120 degrees out of phase with the other two. This creates a more consistent power output compared to single-phase.

• The three hot wires are called phases - typically labeled A, B, and C. The voltage between any two phases is 208V in a 120/208V system.

• A neutral wire carries any imbalance between the phases back to the transformer. The voltage from any phase to neutral is 120V.

• The phases generate three separate magnetic fields rotating around each other. This rotation allows smooth power transfer to motors and large loads.

• A ground wire provides a safe path for current to flow to earth in a fault condition.

Gather Information on the Electrical System

Before troubleshooting, gather as much information as possible about the 3-phase system:

• Age of the building - Older systems may have outdated components.

• Type of power distribution - Is it overhead or underground lines? What size are the feeders?

• Main service panel details - Capacity, voltages, number of phases, etc.

• Subpanel locations - Note all panelboards fed from the main.

• Type of wiring - Aluminum vs copper. Conduit or cable?

• Major equipment - Large motors, air handling units, chillers, etc.

• Power quality issues - History of outages, voltage fluctuations, etc.

• One-line diagram - If available, study the diagram to understand the full system.

Safety Precautions

Always follow safety procedures when working on 3-phase systems:

• Use proper PPE - Eye protection, gloves, clothing.

• De-energize circuits before testing. Follow lockout/tagout procedures.

• Double check wires with a multimeter to confirm they are de-energized.

• Be aware of arc flash hazards. Maintain safe distance.

• Have a fire extinguisher nearby in case of electrical fire.

• If uncomfortable dealing with high voltages, call an electrician.

Troubleshooting Steps

With background knowledge and safety preparations complete, follow these general steps to troubleshoot:

1. Clearly Define the Problem

• What are the exact symptoms? Power fully out? Partial outage? Voltage issues? Tripping breakers?

• Interview occupants about what they were doing when problem occurred. Understanding root cause helps guide troubleshooting.

• Check for any related issues like lighting problems or equipment not operating properly.

2. Review One-Line Diagram

• Note which section of the system is affected by tracing circuits on the diagram.

• This often reveals the general location of the issue - main, subpanel, branch circuit, etc.

3. Check Fuses/Breakers

• Inspect fuses/breakers starting closest to affected area and working upstream toward the main.

• Tighten any loose connections and ensure contacts are clean.

• If main breaker tripped, reset it ONCE to see if it holds. If trips again, problems are upstream or in the main panel.

4. Check Voltages

• Use voltmeter to check phase-to-phase and phase-to-ground voltages at various points.

• Three phase supplies - Should measure 208V phase-to-phase. Voltages significantly higher or lower indicate problems.

• Single phase loads - Should measure 120V phase-to-neutral.

• Compare voltages of working and non-working circuits.

5. Isolate Malfunctioning Loads

• Open points of connection to loads one by one and check if voltages return to normal.

• This isolates the problem to a specific load like a motor or piece of equipment.

• Faulty equipment can damage power supplies.

6. Check Connections

• Loose or corroded connections can cause high resistance and voltage drops.

• Tighten and clean all connections at fuses, breakers, wires, lugs, bus bars, etc through the system.

7. Check Conductors

• Insulation damage or overheating can lead to ground faults and short circuits.

• Shorted windings in motors and transformers distort voltages.

• Megger testing identifies bad insulation before energizing.

8. Start Restoring Power

• Once the problem is identified, start restoring power, section by section.

• Bring the closest section to the problem online first and work downstream.

• Recheck voltages frequently as you restore power.

When to Call an Electrician

If the issue is beyond your skill level to resolve, call a qualified electrician. Some examples:

• Fault in underground feed to building

• Main breaker or panel issue

• Problem traced to primary side of main transformer

• Hazardous conditions - exposed wires, water leaks, etc.

An experienced electrician can use more advanced troubleshooting tools to identify issues. They also have training to work on systems safely while energized. Calling early saves time and prevents damage if the problem worsens.

Conclusion

Troubleshooting 3-phase systems follows a logical progression - gathering information, safety preparations, isolating the problem through voltage checks and visual inspection, and finally restoring power. While complex, any technician can resolve common issues systematically. Know when the problem requires an expert electrician, and don't hesitate to call them. With this approach, you can efficiently restore power and prevent prolonged downtime in older commercial buildings.