Ball Pressure Test for Household Appliances: Standards, Methods and Compliance Requirements

The ball pressure test is a critical heat-resistance evaluation for non-metallic materials used in household and similar electrical appliances, verifying that plastic components do not soften excessively under abnormal heat. This article explains the test principle, applicable standards such as IEC 60335-1 and IEC 60695-10-2, sample requirements, testing procedures, and acceptance criteria used by accredited third-party laboratories worldwide.

Technical Overview

The ball pressure test is a standardized thermal endurance test designed to assess the resistance of thermoplastic and other non-metallic materials to softening when exposed to elevated temperatures. In household appliances, enclosures, insulating barriers, terminal supports, and switch housings are frequently made from polymeric materials whose mechanical and insulating properties degrade as temperature rises. If these parts soften significantly, live parts may become accessible, creepage and clearance distances may be reduced, and the overall safety of the appliance can be compromised.

During the test, a hardened steel ball of 5 mm diameter is pressed against the flat surface of a specimen with a total force of 20 N while both the apparatus and the specimen are maintained at a specified test temperature for a fixed duration. After the load is removed and the specimen is cooled, the diameter of the resulting indentation is measured. A small indentation indicates adequate heat resistance; an oversized indentation indicates that the material softens too much at that temperature and fails the requirement.

The principal standards governing this test for household appliances include:

• IEC 60335-1 — Household and similar electrical appliances — Safety — Part 1: General requirements, which mandates the ball pressure test in Clause 30 for parts of insulating material.
• IEC 60695-10-2 — Fire hazard testing — Part 10-2: Abnormal heat — Ball pressure test method, which defines the test apparatus and procedure.
• GB 4706.1 — the Chinese national standard equivalent to IEC 60335-1, applied for CCC certification of household appliances in China.
• GB/T 5169.21 — the Chinese method standard corresponding to IEC 60695-10-2.
• IEC 62368-1 and related product standards, which apply similar ball pressure requirements to audio/video and information technology equipment.

Testing Samples

The scope of the ball pressure test covers all rigid non-metallic parts of an appliance whose softening could create a safety hazard. Typical sample categories are described below.

Enclosures and External Covers

Outer housings, covers, and panels made of thermoplastic materials such as ABS, PC, PP, or PA. These parts provide protection against access to live parts and must maintain their shape and integrity at operating temperatures. They are typically tested at 75 °C or at a higher temperature determined by the measured temperature rise during normal operation.

Parts Supporting or in Contact with Live Parts

Terminal blocks, switch bodies, connector housings, fuse holders, relay bases, and PCB supports that mechanically retain current-carrying components. Because failure of these parts can directly expose users to electric shock, they are tested at a higher temperature, normally not less than 125 °C.

Insulating Barriers and Additional Insulation

Insulation sheets, bushings, separators, and coil formers that maintain basic, supplementary, or reinforced insulation. These components must retain sufficient rigidity so that creepage and clearance distances are not reduced below permitted values when heated.

Small Components and Decorative Parts

Knobs, handles, indicator lamp holders, fan blades, and decorative trims located near heat sources may also require evaluation if their deformation could affect safety or allow contact with hot or live parts.

Testing Items

The core testing item is the ball pressure resistance test performed at temperatures determined according to the function and location of the component:

• Parts required to retain live parts in position: tested at 125 °C ± 2 °C, or at (40 °C + temperature rise measured during the Clause 11 heating test) if this value is higher, with a minimum of 125 °C.
• Enclosures and other insulating parts: tested at 75 °C ± 2 °C, or at (40 °C + measured temperature rise) where applicable.
• Alternative verification by material class: for certain parts, evidence may be accepted based on material data demonstrating that the material softens at a temperature at least 40 °C above the maximum operating temperature of the part.

Each test result is judged by comparing the measured indentation diameter against the acceptance limit of 2 mm.

Testing Methods

Test Apparatus

The test uses a ball pressure device consisting of a loaded piston terminating in a polished steel ball of 5 mm diameter, arranged so that the ball exerts a downward force of 20 N on the horizontally placed specimen. The apparatus and specimen are placed inside a temperature-controlled oven capable of maintaining the specified temperature within ± 2 °C. Measuring instruments such as a microscope or optical comparator with a resolution of approximately 0.1 mm are used to determine the indentation diameter.

Specimen Preparation

The specimen should be a flat, smooth surface, preferably taken from the finished product or cut from a representative sample of the same material. The thickness of the specimen should be at least 2.5 mm; thinner samples may be stacked to achieve the required thickness. Prior to testing, the specimen is conditioned as specified, and the test surface is positioned horizontally beneath the ball.

Test Procedure

• Set the oven to the specified test temperature and allow the ball pressure apparatus to reach thermal equilibrium, typically for at least 1 hour or as required by the standard.
• Place the specimen on the support surface so that the ball contacts the flat test surface, and apply the 20 N load.
• Maintain the load for 60 minutes ± 2 minutes at the specified temperature.
• Remove the specimen and, within 10 seconds, immerse it in water at approximately 20 °C to cool for a period between 6 and 10 minutes.
• Measure the diameter of the indentation within a defined short interval after cooling, taking the maximum dimension in any direction across the impression.

Evaluation and Acceptance Criteria

The test is considered passed if the diameter of the indentation does not exceed 2.0 mm. If the measured diameter exceeds 2.0 mm, the material fails the ball pressure requirement at that temperature, and the manufacturer must select a more heat-resistant material or redesign the part to reduce its operating temperature. Test reports issued by accredited third-party laboratories document the test temperature, load, duration, and measured indentation diameter for each specimen.

Applications

The ball pressure test is applied across the full range of household and similar electrical appliances, including:

• Kitchen appliances: rice cookers, electric kettles, toasters, blenders, microwave ovens, coffee machines, and air fryers.
• Cleaning and climate appliances: vacuum cleaners, washing machines, dishwashers, electric fans, heaters, and dehumidifiers.
• Personal care appliances: hair dryers, curling irons, electric irons, and massagers.
• Small power and heating tools with molded plastic enclosures and terminal assemblies.

Beyond household appliances, the same test method is widely used for certification of IT equipment, luminaires, low-voltage switchgear, plugs and socket-outlets, and components such as switches and connectors under IEC, EN, GB, UL, and JIS standards. Manufacturers rely on ball pressure test data during material selection, design verification, and regulatory certification, including CB scheme testing and national market-access approvals.

FAQ

What is the ball pressure test used for?

It evaluates the resistance of non-metallic materials, mainly thermoplastics, to softening at elevated temperatures. In household appliances it ensures that enclosures and parts retaining live parts do not deform to the point of creating electric shock or fire hazards.

What are the key test parameters?

A 5 mm steel ball, a 20 N force, a test temperature of typically 125 °C for live-part retainers or 75 °C for enclosures (or a temperature based on measured temperature rise), and a loading duration of 60 minutes.

What is the pass criterion?

The indentation diameter measured after cooling must not exceed 2.0 mm.

Why are two different temperatures specified?

Parts that mechanically retain live parts carry a higher risk if they soften, so they are tested at a minimum of 125 °C. Enclosures and other insulating parts are generally tested at 75 °C, unless the temperature rise measured during normal operation indicates that a higher test temperature is necessary.

Can material data replace the test?

In some product standards, compliance may alternatively be demonstrated if documentary evidence shows that the material softens at a temperature at least 40 °C above the maximum temperature the part reaches in operation. Otherwise, testing on the actual part is required.

How should specimens be prepared when the part is curved or thin?

Whenever possible, a flat area of the finished part is tested. If the finished part does not provide a suitable flat surface or sufficient thickness, a specimen cut from a plate of the same material, at least 2.5 mm thick, may be used.

Which certifications require the ball pressure test?

The test is part of safety evaluations under IEC 60335-1 and its parts 2 series, GB 4706.1 for CCC certification, and equivalent regional standards, and it is routinely performed during CB scheme assessments by accredited third-party laboratories.