Among arc faults, series arcs are especially easy to overlook. Unlike phase-to-ground or phase-to-phase short circuits, which generate enormous currents, a series arc hides inside the load circuit, manifesting as unstable contact, intermittent discharge, and abnormal waveforms.
The danger of this type of risk is that the current may not look alarming, yet the temperature at the arc point can be extremely high. When the arc recurs over a long period, it is enough to cause insulation carbonization, material damage, and fire hazards.
1. Where Do Series Arcs Typically Occur?
Series arcs commonly occur at loose terminal connections, poor contact between plugs and sockets, broken conductor strands, degraded switch contacts, poorly crimped joints, and oxidized line connection points. These locations may not be completely disconnected from the start, but rather remain in an unstable contact state.
When load current flows through an unstable contact point, intermittent discharge may form. On site, it may only appear as occasional flicker, localized heating, abnormal device restarts, or faults that are difficult to explain.
2. Why Isn't the Series Arc Current Necessarily Large?
Because a series arc lies inside the load circuit, the current is limited by the load. Even when arcing occurs at a contact point, the total circuit current may still remain within the normal operating range and may not reach the trip condition of the circuit breaker's overload protection.
This is the root cause of series arcs being easily missed: traditional protection targets high-current faults, whereas the danger of a series arc is reflected more in localized high temperature, discontinuous waveforms, and sustained recurrence.
3. What Are the Signal Characteristics of Series Arcs?
Series arcs tend to be intermittent, random, and load-dependent. They may show anomalies in certain current half-cycles, and may appear or disappear with vibration, temperature, and load variations.
In terms of signals, they may appear as current waveform distortion, discontinuity points, high-frequency pulses, increased noise density, and half-cycle anomalies. These features are hard to see if only the ordinary RMS current value is observed.
4. Why Is Half-Cycle-Level and Waveform-Level Identification Needed?
The key risk of series arcs is hidden in waveform details. Half-cycle-level identification can reveal abnormal intermittence, spikes, or unstable discharge within each cycle; waveform-level identification can further distinguish normal switching disturbances and load starts from dangerous arcs.
If only minute-level or second-level statistics are performed, many details will be averaged away. A truly effective algorithm must examine both transient features and time persistence at the same time.
5. How Does FEXLINK Approach Series Arc Detection?
FEXLINK believes that series arc detection cannot rely on a single frequency point or a single threshold. FEXLINK combines low-frequency electrical parameters, high-frequency events, harmonic variations, half-cycle waveforms, time density, and scenario-based self-learning to produce an explainable arc risk index.
Especially in scenarios such as charging piles, motors, temporary site power, distribution cabinets, and communication base stations, load disturbances are complex, and multi-dimensional features are needed to filter out false alarms.
Conclusion: The Difficulty of Series Arcs Lies in "High-Risk Localized Discharge" Rather Than "Large Current"
Series arcs are most easily missed because they may not trigger traditional overload protection, yet they can continuously generate high-temperature and discharge risks locally. To identify series arcs, analysis must move beyond current magnitude to waveform characteristics and time-behavior analysis.
