High Current Impulse Making and Breaking Test: Principles, Standards, and Procedures

The high current impulse making and breaking test is a critical type test used to verify that switching devices such as contactors, relays, switches, and circuit breakers can safely close onto and interrupt severe overcurrent conditions. Performed by accredited third-party laboratories in accordance with IEC 60947, IEC 60898, GB/T 14048, and UL standards, the test evaluates contact welding resistance, arc extinction capability, and structural integrity under worst-case electrical stress. This guide explains the test principle, applicable standards, sample requirements, test procedures, acceptance criteria, and typical applications for engineers and compliance professionals.

Technical Overview

The high current impulse making and breaking test is a destructive type test performed on low-voltage switching devices to verify their ability to establish (make) and interrupt (break) circuits carrying currents substantially higher than the rated operational current. In real installations, contactors and switches must close onto locked-rotor motor currents, plugging and inching duties, or fault currents that may reach eight to twelve times the rated value. These events generate intense arcing, contact erosion, and powerful electrodynamic forces that can weld contacts, damage arc chutes, or cause phase-to-phase flashover if the device is not properly designed.

During the making operation, a pre-strike arc forms as the contacts approach each other, followed by contact bounce and the risk of microwelding at the first current peak. During the breaking operation, an arc is drawn between separating contacts and must be extinguished quickly, after which the device must withstand the transient recovery voltage without re-ignition. The test reproduces these worst-case stresses under precisely controlled laboratory parameters, including test voltage, prospective current, power factor (for AC) or time constant (for DC), and the degree of current asymmetry.

The test is conducted according to internationally recognized standards, including IEC 60947-1 (general rules for low-voltage switchgear and controlgear), IEC 60947-4-1 (contactors and motor starters), IEC 60947-5-1 (control circuit devices), IEC 60947-3 (switches and disconnectors), IEC 60947-2 and IEC 60898 (circuit breakers), the GB/T 14048 series adopted in China, and relevant UL standards such as UL 508 and UL 489. Conformity is typically demonstrated through type testing at accredited third-party laboratories.

Testing Samples

Samples submitted for high current impulse making and breaking testing must be new, clean, complete products in normal service condition, mounted and wired according to the manufacturer's installation instructions and the relevant standard. Conductor cross-sections, cable lengths, and enclosure configuration are controlled because they influence test severity and reproducibility.

Contactors and Motor Starters

Electromechanical contactors, direct-on-line starters, star-delta starters, and reversing starters are the most common test subjects. Testing severity is defined by the utilization category, such as AC-3 (starting and switching off squirrel-cage motors during running), AC-4 (starting, plugging, and inching), or DC categories. AC-4 duty is the most severe, typically requiring making and breaking at twelve times the rated operational current.

Control Circuit Devices and Relays

Control relays, auxiliary contact blocks, and electromechanical relays covered by IEC 60947-5-1 and IEC 61810 are tested to confirm reliable switching of overload and fault-level currents in control circuits, including verification that contacts do not weld under asymmetric peak currents.

Switches, Disconnectors, and Fuse-Combination Units

Manually operated switches, switch-disconnectors, and switch-fuse units per IEC 60947-3 are tested for making and breaking performance under overload and fault-related current conditions, verifying operator safety and arc containment.

Circuit Breakers

Molded case circuit breakers, miniature circuit breakers, and motor protection circuit breakers are evaluated for rated short-circuit making capacity and breaking capacity. The making capacity is defined as a multiple of the symmetrical breaking current, reflecting the asymmetric peak that includes the DC offset component.

Household and Similar Electrical Appliances

Appliance switches, household circuit breakers, and similar devices are tested to the applicable IEC, EN, GB, UL, or JIS product standards to verify safe switching behavior under abnormal current conditions encountered in residential environments.

Testing Items

Depending on the product standard and utilization category, a high current impulse making and breaking test program typically includes the following verification items:

• Rated making capacity verification at the specified test voltage and asymmetric peak current
• Rated breaking capacity verification, including arcing time and successful extinction under transient recovery voltage
• Combined make-break sequences at utilization category currents, for example ten times rated operational current for making and eight times for breaking under AC-3 duty
• Verification that contacts do not weld and that the device releases and operates normally after each operation
• Dielectric withstand verification after the switching test sequence
• Inspection of contact erosion, overtravel, arc chute condition, and structural integrity after testing
• Temperature rise or voltage drop verification following switching tests where required by the standard
• Conditional short-circuit performance when the device is coordinated with a specified short-circuit protective device

Testing Methods

Test Circuit Configuration and Calibration

The test station consists of a high-capacity power source (a short-circuit generator or test transformer), adjustable series resistors and reactors for setting the prospective current and power factor or time constant, a calibrated making switch, and the device under test connected with specified conductors. Before testing, calibration oscillograms are recorded with the device replaced by a low-impedance link or with the making switch closed. These oscillograms verify the prospective RMS current, the peak current and its asymmetry, the power factor (commonly determined from the decay of the DC component), and the recovery voltage. All parameters must fall within the tolerances defined by the applicable standard, typically on the order of plus or minus five percent for current.

Test Parameters and Conditions

Key controlled parameters include:

• Test voltage: equal to the rated operational voltage, maintained within the tolerance band of the standard
• Test current: a defined multiple of the rated operational current, calibrated from the oscillogram
• Power factor or DC time constant: matched to the prospective current level, with lower power factors required at higher currents to reproduce realistic fault conditions
• Current asymmetry: expressed as a peak factor relating the asymmetric making peak to the symmetrical RMS value, generally between approximately 1.5 and 2.2 depending on the power factor
• Duration of current flow during making operations, limited by an auxiliary interrupting device to protect the circuit while stressing the sample realistically
• Time interval between successive operations, commonly five to ten seconds for contactor tests, extended where necessary for arc chamber recovery

Test Sequence and Procedure

For contactors and motor starters tested to IEC 60947-4-1, the making and breaking capacity verification typically consists of fifty making operations and fifty breaking operations at the utilization category currents, performed at defined intervals. Each making operation closes the contactor onto the preset prospective current; each breaking operation establishes the current and then opens the contactor under load. For circuit breakers tested to IEC 60947-2 or IEC 60898, standardized operating sequences such as O - t - CO - t - CO are used, where O denotes an automatic break, CO denotes a close followed by an automatic break, and t is a specified recovery time such as three minutes. Control circuits are energized at rated control supply voltage, and the sample must operate with its own intrinsic operating times, without external assistance.

Measurement and Instrumentation

High-speed transient recorders or digital oscilloscopes capture current and voltage waveforms through Rogowski coils, coaxial shunts, and high-voltage probes or dividers. The recorded oscillograms are used to verify prospective current, arcing time, arc voltage, arc extinction at or near current zero, the recovery voltage withstand period, and the absence of re-ignition or flashover. High-speed imaging may supplement electrical measurements during development testing to analyze arc movement into the deion plates.

Acceptance Criteria

A sample is considered to have passed the test when all of the following conditions are met:

• Complete extinction of the arc within the time limits of the standard, with no sustained arcing or re-ignition under recovery voltage
• No flashover between poles, between phases, or to exposed conductive parts and earth
• No contact welding that prevents the device from opening or releasing when the control supply is de-energized
• No significant mechanical damage; arc chutes, arc runners, and insulating parts remain intact and functional
• Dielectric withstand verified after the test sequence at the specified test voltage
• Movable contact overtravel still present and normal operation confirmed after testing
• No emission of flames or molten material that could create a hazard in service

Applications

High current impulse making and breaking testing supports the entire product life cycle of switching devices across many industries:

• Product certification and market access: type testing for CB Scheme certification, national safety marks, and factory acceptance, conducted by accredited third-party laboratories
• Research and development: comparative evaluation of contact materials such as silver-nickel and silver-tin oxide alloys, optimization of magnetic blowout structures, arc chute geometry, and contact spring forces
• Design verification: confirmation that a new contactor or breaker platform meets its declared utilization category and breaking ratings before production release
• Manufacturing quality control: periodic design revalidation, supplier qualification, and batch surveillance testing to detect material or process drift
• Motor control centers, pump and fan control, compressor switching, capacitor bank switching, mining, marine, railway, and photovoltaic switching applications where reliable fault-current switching is essential

FAQ

What is the difference between making capacity and breaking capacity?

Making capacity is the ability of a device to close onto a circuit carrying a high prospective current, including the asymmetric first peak with its DC offset, and primarily stresses resistance to contact welding and electrodynamic repulsion. Breaking capacity is the ability to interrupt an established current against the transient recovery voltage, which primarily stresses arc extinction and dielectric recovery of the contact gap.

How are the test currents determined?

For contactors, the test current is a multiple of the rated operational current defined by the utilization category; for example, AC-3 duty generally requires making at ten times and breaking at eight times the rated operational current, while AC-4 duty requires twelve times for both. For circuit breakers, breaking capacity ratings such as Icu are declared by the manufacturer, and the making current is derived from the symmetrical current using the peak factor associated with the test circuit power factor.

Why is the power factor or time constant so strictly controlled?

The power factor of an AC test circuit determines the DC offset and therefore the asymmetrical peak current, the arc energy, and the electrodynamic forces applied to the device. Calibration against standard tolerances ensures that every laboratory applies equivalent, reproducible stress, making results comparable across test stations.

How is contact welding detected during the test?

After each operation, the control supply is removed and the device must release and reset by its own mechanism. Failure to drop out, loss of contact overtravel, or abnormal release force indicates welding. Post-test disassembly and contact inspection are also performed to confirm the condition of contact surfaces.

Can one sample be used for multiple test sequences?

Generally not. The test is destructive and progressively degrades contacts and arc chambers. Standards therefore require new samples for each distinct test sequence, and only preconditioning explicitly specified by the standard, such as prior temperature-rise testing in certain programs, is permitted.

What are the most common failure modes?

Typical failures include contact welding, sustained arcing or re-ignition after current zero, phase-to-phase or pole-to-earth flashover, destruction of arc chutes and deion plates, excessive contact erosion, and inability to pass the post-test dielectric withstand verification.

Are GB/T standards equivalent to IEC standards for this test?

The GB/T 14048 series is substantially aligned with the corresponding IEC 60947 series in test circuits, parameters, sequences, and acceptance criteria. Manufacturers targeting both international and domestic markets should confirm any national deviations with accredited third-party laboratories before initiating a test program.