Okay, this is a fascinating and humbling scenario. You've spent 40 years preaching a tenant of electrical behavior, and real-world evidence is challenging it. Let's break down why your understanding, while generally accurate, might not fully explain these events, and what might be happening with these capacitor bank failures

Why "Load-Side Faults Cause Tripping" Is Still Mostly True...But Not Always.
Fundamental Principle

The vast majority of breaker trips are due to overcurrent (overload or short circuit) or ground faults caused by something downstream of the breaker (on the load side). This is the core design principle of circuit breakers. They're designed to protect wiring and equipment from being overloaded or having dangerous shorts.

Breakers React to Conditions

Breakers detect current flow and voltage imbalances, and respond when those parameters exceed their safety thresholds. These conditions are usually caused by something on the load side.

Why Your Understanding Needs Adjustment in This Specific Case

The key here is the primary-side issue (the malfunctioning capacitor bank) and the differential frequency (DF) breakers in the residential panels. Here's why a primary-side problem can cause secondary-side (residential) breakers to trip, especially DF breakers:

Power Quality Issues

A malfunctioning capacitor bank, particularly one arcing or behaving erratically, is a

significant power quality disturbance on the primary distribution system. This disturbance can manifest in several ways: Voltage Sags/Surges

The arcing and erratic switching can cause rapid voltage dips (sags) and potentially surges on the primary lines.

Harmonics

The arcing generates high-frequency harmonic distortion. Harmonics are multiples of the fundamental 60Hz frequency, and they can wreak havoc on electrical equipment.

Voltage Transients/Noise

Very short-duration, high-voltage spikes can occur due to the switching and arcing.

Differential Frequencies

DF breakers are very sensitive to frequencies that are outside of the 60hz power supplied by the poco.

Capacitor Bank Function

Capacitor banks are installed to improve the power factor on the distribution system. Their purpose is to reduce line losses and improve voltage regulation. When they fail, they can cause significant disruptions.

Capacitive Load Switching

Switching capacitor banks can cause voltage transients. Normally, these are managed by pre-insertion resistors or controlled switching devices. A faulty switch likely caused uncontrolled transients.

DF Breakers and Power Quality

This is the crucial piece. DF breakers are designed to detect differential frequencies, meaning they respond to frequencies outside the normal power frequency. The arcing and switching in the faulty capacitor bank are generating high-frequency noise and transients that the DF breakers are interpreting as a fault. The breaker is reacting to a disturbance, not necessarily a fault in the traditional "short circuit to ground" sense.

Why It Affected Multiple Houses, Even on Different Phases and Circuits



Propagation Through the Grid

The disturbances generated by the capacitor bank propagate through the distribution network. The entire distribution system is interconnected. Voltage sags, surges, and harmonics don't stay neatly confined to a single phase or circuit. They can travel through transformers and along lines, affecting a wide area.

DF Breaker Sensitivity

DF breakers are designed to be sensitive to low-level frequencies. This sensitivity, while intended to protect against serious ground faults, can also make them susceptible to nuisance tripping from power quality disturbances.

Why Other Breakers Might Not Trip



Standard Breakers

Standard overcurrent breakers (non-DF) respond to magnitude of current. A voltage sag or harmonic distortion might not cause enough overcurrent to trip them.

AFCI Breakers

AFCI breakers are designed to detect arcing within the building wiring. While the capacitor bank arcing is generating disturbances, it's unlikely to mimic the specific arc signatures that AFCIs are looking for within the protected circuit.

In summary

While your understanding of breakers tripping due to load-side faults is generally correct, this situation highlights a crucial exception: power quality disturbances on the primary distribution system can cause sensitive breakers like DF breakers to trip, even if there's no actual fault in the customer's wiring.

What to Do



Acknowledge the Complexity

Embrace the fact that electrical systems are complex and interconnected. There are always exceptions to the rules.

Learn More About Power Quality

Deepen your understanding of power quality issues, harmonics, transients, and how they affect equipment.

Work with the POCO

Collaborate with the utility to understand how they are managing power quality on the distribution system.

Consider Power Quality Monitoring

For customers experiencing persistent issues, recommend power quality monitoring to identify and mitigate the source of the disturbance.*

Re-evaluate DF Breaker Usage: While DF breakers are important for safety, their increased sensitivity can lead to nuisance tripping in environments with power quality issues.This experience is a valuable reminder that electrical troubleshooting requires a holistic understanding of the entire electrical system, from the generation source to the point of use. Thanks for sharing your experience - it's a great learning opportunity for everyone. Flag for review