Arc-over the sudden electrical discharge that occurs when the HF field in a welding machine breaks down and a spark or arc jumps between the electrode and the lower table is the most dramatic and alarming fault that operators of HF welding machines experience. In a UAE tent manufacturing or tarpaulin fabrication workshop, arc-over is also one of the most frequently misdiagnosed problems sometimes treated as a machine fault when it is actually a settings or fabric issue, and sometimes dismissed as a settings issue when it actually indicates developing machine component failure.

This guide explains arc-over systematically what it is, why it happens, how to distinguish between settings-related, fabric-related, and machine-related arc-over, and what to do when it occurs. Watad Al Khaima supplies HF welding machines and technical support across the UAE and Middle East.

What Is HF Welding Arc-Over and Why Does It Happen?

In normal HF welding operation, the electromagnetic field generated between the electrode and the lower table heats the PVC fabric through dielectric loss the PVC compound’s dipolar molecules rotate in the alternating field, generating internal heat through molecular friction. The field remains contained within the fabric stack between electrode and table, producing controlled, localised heating at the weld zone.

Arc-over occurs when the electric field intensity between the electrode and the lower table exceeds the dielectric strength of the material stack the field “breaks down” and a direct electrical discharge (arc) jumps between the two metal surfaces through or around the fabric. This arc is instantaneous, extremely high temperature, and burns through any material it contacts creating a hole or burn mark in the fabric, potential damage to the electrode face, and risk of fire if flammable solvent residues are present in the workshop.

The physics are straightforward: arc-over happens when the voltage between electrode and table exceeds the breakdown voltage of whatever is between them. Three factors determine breakdown voltage: the gap between electrode and table (smaller gap = lower breakdown voltage), the dielectric properties of the material stack (weaker dielectric = lower breakdown voltage), and the applied field strength (higher power = higher field intensity pushing closer to breakdown).

Types of Arc-Over: Where It Occurs

Identifying where the arc occurs provides the first diagnostic clue about its cause:

Through the fabric (fabric arc-over): The arc burns directly through the PVC fabric stack in the weld zone leaving a small burn hole or carbonisation mark in the fabric at the arc point. This type most commonly indicates power settings too high for the fabric or a local material defect.

Around the fabric edge: The arc jumps from electrode to table at the fabric edge rather than through the fabric indicating the fabric is not positioned correctly under the electrode, or the electrode overhang beyond the fabric edge is excessive. No damage to the fabric body but potential burn marks on the lower table.

Through the FEP film: The arc burns through the FEP release film often leaving a small hole in the film without significant fabric damage. Indicates the FEP film is degraded or too thin for the operating conditions, or a localised defect in the film is reducing its dielectric strength.

Between electrode body and lower table (not at weld zone): The arc occurs at the edge or body of the electrode rather than at the active weld face indicating machine geometry issues, electrode mounting problems, or machine component faults.

Settings-Related Arc-Over: The Most Common Cause

The majority of arc-over events in UAE production workshops are settings-related occurring because the combination of power output and dwell time is driving the field intensity beyond the breakdown threshold of the specific fabric being welded. As covered in our machine settings guide, the interaction of power, dwell, and fabric specification must be correctly calibrated.

Power too high for fabric specification

Running the machine at power output that is too high for the fabric weight being welded creates field intensities that approach the fabric’s dielectric breakdown threshold. Even if the settings were working correctly for a heavier fabric previously used on the machine, switching to lighter fabric without reducing power creates arc-over risk. Solution: reduce power output by 10–15% and re-test on scrap fabric before resuming production.

Dwell time too long

Excessive dwell time allows cumulative heat buildup in the fabric that reduces the PVC compound’s dielectric strength hot, nearly-molten PVC has lower breakdown voltage than cool, solid PVC. When the fabric reaches this partially molten state, the same power level that was safe during the early part of the dwell cycle can cause arc-over as dielectric strength falls. Solution: reduce dwell time in 0.2-second increments and re-verify with peel testing.

UAE summer heat compound effect

As described in our settings guide, UAE summer ambient temperatures pre-warm the fabric before welding, reducing the power and dwell time needed to reach welding temperature. Machine settings calibrated in winter may be excessive in summer what was a correct setting at 22°C workshop temperature can cause arc-over at 40°C when the fabric enters the weld cycle already warm. Re-calibrate settings at seasonal temperature changes.

Fabric and Material-Related Arc-Over Causes

Localised fabric defects

Thin spots, voids in the PVC compound, and areas of reduced coating weight in the fabric create localised zones of lower dielectric strength where the field intensity that the surrounding fabric can sustain easily causes breakdown at the defect. Arc-over that occurs at random, non-repeating locations across a production run (rather than consistently at the same position relative to the electrode) often indicates localised fabric quality variation. If this pattern is observed consistently across a roll, contact the fabric supplier for quality review.

Contamination between fabric layers

Metal particles, conductive dust, or moisture between the fabric layers in the weld zone dramatically reduce dielectric strength and can cause arc-over at power levels well below those that would cause breakdown in clean, dry fabric. UAE workshop dust particularly in facilities near construction sites or industrial areas can introduce fine conductive particles to the weld zone. Inspect and clean fabric surfaces before welding if contamination is suspected.

Degraded FEP film

FEP film that has been used beyond its effective service life develops micro-perforations and surface degradation that reduce its dielectric contribution to the electrode-to-fabric stack. As the film’s contribution to breakdown voltage is lost at these degraded zones, arc-over through the film becomes more likely. Inspect FEP film condition and replace at the first signs of surface degradation as detailed in our FEP film thickness guide.

Machine-Related Arc-Over: When It Indicates a Fault

While most arc-over events are settings or fabric related, some patterns indicate developing machine component faults that require professional technical attention:

Arc-over at reduced power settings that previously were safe: If arc-over now occurs at power levels that worked correctly without incident previously, the machine’s power regulation circuitry may be providing higher actual output than the control panel indicates potentially due to a faulty power control component.

Recurring arc-over at the same electrode position: Consistent arc-over at a specific location relative to the electrode (e.g., always at one end of the bar) may indicate electrode surface damage, uneven electrode contact, or a fault in the electrode mounting that creates a localised field hot spot.

Arc-over accompanied by unusual sounds or smells from inside the machine: Any arc-over event accompanied by electrical burning smell from the machine enclosure (not from the fabric) or unusual noise requires immediate shutdown and professional inspection it may indicate internal arcing within the machine’s high-voltage circuits.

Frequent arc-over despite correct settings verified by fresh calibration: If arc-over persists after correct settings re-calibration with verified-quality fabric and fresh FEP film, a machine fault (capacitor degradation, frequency drift, earth fault) is the likely cause professional maintenance inspection is required.

UAE-Specific Factors That Increase Arc-Over Risk

Summer temperature: As described above pre-warmed fabric requires reduced settings to avoid the cumulative heat effect that triggers arc-over. Re-calibrate at seasonal temperature changes.

Humidity variation: UAE coastal workshops experience humidity variation that affects fabric moisture content fabric with elevated moisture content has lower dielectric strength and is more arc-over prone. Production during UAE winter fog periods (December–February in some coastal areas) may require additional power reduction.

Dust contamination: UAE workshop environments accumulate conductive mineral dust faster than European equivalents. Weekly internal machine cleaning (per our maintenance guide) and fabric surface inspection before welding reduce dust-related arc-over risk.

Prevention and Recovery Procedure

Immediate action when arc-over occurs

Press the machine’s emergency stop immediately do not continue the weld cycle

Check for fire risk any smouldering fabric or FEP film must be extinguished before continuing. Keep a CO₂ extinguisher within reach of all HF welding stations

Allow the machine to cool for 2–3 minutes before opening the electrode zone

Inspect and clean the electrode face arc-over leaves a carbon deposit on the electrode that must be removed before further production (see maintenance guide for cleaning procedure)

Replace the FEP film any film present during an arc-over has been compromised and must not be reused

Reduce power by 10% and re-calibrate with peel testing on scrap before resuming production

Prevention through correct practice

The arc-over prevention programme combines correct machine settings calibrated for the current fabric and UAE seasonal conditions, regular FEP film replacement before degradation rather than at failure, fabric surface inspection for contamination before welding, and the maintenance schedule detailed in our maintenance guide particularly monthly internal cleaning to remove the conductive dust that accumulates in UAE workshop environments.

Conclusion

HF welding arc-over in UAE fabric production is most commonly a settings issue power too high, dwell too long, or UAE summer temperatures requiring recalibration that was not performed. Correct diagnosis starts with identifying where the arc occurs, then systematically eliminating settings, fabric, FEP film, and machine causes in order of likelihood. Machine-related arc-over patterns recurring at the same location, appearing at previously safe power levels, accompanied by machine-side symptoms require professional technical attention rather than further settings adjustment. The prevention programme combining correct settings, regular FEP film replacement, fabric surface inspection, and the UAE-adapted maintenance schedule minimises arc-over occurrence across all production conditions. Watad Al Khaima provides HF welding machine supply and technical support for UAE fabric manufacturing. Contact our team for machine support or consumables supply.