Date | 2026-05-27 08:23:47
Inside every low-voltage circuit breaker, the arc chamber is the frontline of fault interruption. The moment electrical contacts separate under short-circuit conditions, an electric arc is generated — with temperatures reaching several thousand degrees Celsius, accompanied by intense thermal shock, ultraviolet radiation, and high-velocity ionized gases.
Within this environment, insulation components such as arc chamber partitions, support plates, and insulating barriers made from BMC (Bulk Molding Compound) must withstand repeated arc exposure while maintaining both structural integrity and electrical insulation performance.
One critical parameter defines this capability:
Arc Resistance
In practical engineering terms, arc resistance answers a simple but vital question:
How long can a material resist forming a conductive path under continuous arc exposure?
Arc resistance is commonly evaluated according to:
GB/T 1411
IEC 61621
The test method is straightforward but extremely demanding.
Two tungsten electrodes are positioned at a specified distance above the material surface. A high-voltage arc (typically 15kV or higher) is continuously applied, and the time required for the material surface to form a conductive track or electrical breakdown is recorded in seconds.
During testing:
The arc repeatedly attacks the material surface
Localized carbonization occurs
Thermal decomposition accelerates
Materials that quickly develop carbonized conductive tracks show poor arc resistance. Materials capable of resisting conductive path formation achieve significantly longer arc resistance times.
According to the internal technical specification Q/JTJ0001-2025 from Wenzhou Jintong Complete Appliances Co., Ltd., all BMC/SMC material grades are designed to achieve:
Arc Resistance ≥180 seconds
This means the material can withstand at least three minutes of continuous arc exposure under standardized conditions before forming a conductive surface path.
In actual circuit breaker operation, short-circuit interruption arcs typically last only:
A few milliseconds
Up to several tens of milliseconds
At first glance, 180 seconds may seem excessive. However, arc resistance testing is not intended to simulate a single switching event.
Instead, it evaluates:
Throughout a circuit breaker’s service life, insulation components may experience:
Dozens
Or even hundreds
of fault interruption events.
Although each arc exposure is brief, the damage is cumulative.
Over time:
Resin surfaces gradually decompose
Carbonized regions expand
Leakage tracking paths may eventually form
Once a conductive track connects high and low potential regions, the arc chamber loses its insulation capability.
From an engineering perspective, a material rated at ≥180 seconds provides a substantial long-term safety margin against cumulative arc degradation throughout the product lifecycle.
The outstanding arc resistance of BMC materials comes from the synergistic interaction between:
High inorganic filler loading
Crosslinked thermosetting resin systems
Typical BMC formulations contain:
60–75% inorganic fillers
Common fillers include:
Aluminum hydroxide (ATH)
Calcium carbonate
Silica powders
Under arc exposure, aluminum hydroxide begins decomposing around 200–300°C, releasing chemically bound water while absorbing significant heat energy.
This process provides several critical benefits:
Surface temperature reduction
Arc plasma dilution
Suppression of conductive ion concentration
The decomposition residue, aluminum oxide (Al₂O₃), forms a stable ceramic-like insulating layer on the material surface, helping isolate the underlying resin from direct arc attack.
Unlike thermoplastics, thermosetting polyester resin forms a highly crosslinked three-dimensional network after curing.
Under extreme heat:
Thermoplastics tend to melt and flow
Continuous carbonized conductive films may form
BMC behaves differently.
Its crosslinked structure tends to generate:
Discontinuous carbon residues
Non-uniform char structures
Combined with the large volume fraction of inorganic fillers, conductive carbon pathways struggle to connect into continuous tracks.
This is a major reason why BMC materials can sustain:
Arc Resistance ≥180 seconds
under standardized testing conditions.
When selecting BMC insulation materials for circuit breaker arc chambers, engineers should evaluate multiple safety parameters together.
Arc chambers experience both:
Electrical arc exposure
Thermal flame exposure
Recommended baseline requirements include:
Arc Resistance ≥180s (GB/T 1411 / IEC 61621)
Glow Wire Test ≥960°C (GB/T 5169.12)
Higher aluminum hydroxide loading generally improves arc resistance performance.
Material suppliers should be able to explain:
Filler types
Approximate loading ratios
Flame-retardant mechanisms
Arc resistance results are heavily influenced by:
Electrode spacing
Applied voltage
Surface preparation
Test environment
Reliable data should always reference recognized standards such as:
GB/T 1411
IEC 61621
Wenzhou Jintong Complete Appliances Co., Ltd. specializes in high-performance:
BMC materials
SMC materials
Thermosetting composite insulation solutions
for:
Low-voltage electrical systems
Circuit breaker insulation components
Arc chamber structures
High-reliability electrical applications
Our BMC materials are engineered for:
Arc resistance
Flame retardancy
Electrical insulation stability
Long-term durability under severe electrical stress
📩 Contact:
Email: wendy.qiu@smcbmc.com
Tel: +86 13868305300
