Marking durability testing for household electrical appliances verifies that rating plates, warning labels, and control markings remain legible and securely attached throughout the product's service life, as required by Clause 7 of IEC 60335-1 and its national adoptions such as EN 60335-1, GB 4706.1, UL 60335-1, and JIS C 9335-1. The assessment uses a standardized rubbing sequence involving water, petroleum spirit, and the finger to simulate everyday cleaning, incidental solvent contact, and mechanical wear. This article explains the technical basis, test samples, procedures, acceptance criteria, and practical applications of the test for manufacturers, design engineers, and compliance professionals.
Technical Overview
Household and similar electrical appliances must carry durable, legible markings that communicate essential safety information to installers, service personnel, and end users. Clause 7 of IEC 60335-1 (Household and similar electrical appliances – Safety – Part 1: General requirements) and its equivalent regional standards, including EN 60335-1, GB 4706.1, UL 60335-1, and JIS C 9335-1, specify the required marking content, such as rated voltage, rated frequency, rated power input, manufacturer name or trademark, model designation, the symbol for class II construction, IP codes where applicable, and safety warnings.
Clause 7.14 of these standards requires all markings to be durable and legible throughout the expected life of the appliance. Compliance is verified through a standardized rubbing procedure: the marking is rubbed by hand for 15 seconds with a cloth soaked in water, followed by 15 seconds with a cloth soaked in petroleum spirit, defined in the standard as aliphatic solvent hexane. Earlier editions of IEC 60335-1 and the corresponding GB 4706.1 standard additionally specify a final 15-second rub with the finger to simulate prolonged handling.
After the rubbing sequence, the marking must remain clearly legible, nameplates must not be easily removable, and labels must not show curling or lifting at the edges. Marking durability testing is therefore a fundamental checkpoint in appliance safety evaluation, since an illegible rating plate or a detached warning label can compromise safe installation, operation, and maintenance.
Testing Samples
Rating Plates and Nameplates
Adhesive-backed metal, aluminum foil, or polyester nameplates carrying the electrical ratings and manufacturer identification are the most common samples. These plates are evaluated for both marking durability and adhesive performance, since detachment or edge curling constitutes a failure regardless of whether the printed information survives the rubbing test.
Warning Labels and Safety Markings
Labels warning of hot surfaces, live parts, or required disconnection before servicing are tested because they directly support safe user behavior. Deterioration of these markings is treated as a significant safety deficiency during appliance evaluation.
Printed and Painted Control Markings
Silk-screen printed, pad-printed, or painted markings on plastic control panels, knobs, switch actuators, and indicator surrounds are included in the scope. These markings are particularly vulnerable to abrasion and solvent exposure during routine cleaning of the appliance exterior.
Molded, Engraved, and Laser-Etched Markings
Markings formed directly in the material by molding, stamping, engraving, or laser etching generally offer the highest durability. Under current editions of IEC 60335-1, the petroleum spirit rub is not applied to markings that are molded or engraved into the material, although these markings are still assessed for legibility and permanence by inspection.
Testing Items
The marking durability assessment comprises the following verification points, each of which is judged as pass or fail against the requirements of Clause 7.14:
- Water rub resistance: the ability of the marking to withstand rubbing with a water-soaked cloth, simulating cleaning with a damp cloth.
- Solvent rub resistance: the ability of the marking to withstand rubbing with a cloth soaked in petroleum spirit, simulating contact with household solvents and grease-cutting cleaning agents.
- Finger rub resistance: resistance to mechanical abrasion from repeated handling, as required by earlier editions of IEC 60335-1 and by GB 4706.1.
- Adhesion and edge stability: verification that nameplates and labels cannot be easily removed and show no curling, blistering, or lifting at the edges after testing.
- Post-test legibility: confirmation that characters, digits, and symbols remain clearly readable under normal illumination from the intended viewing position.
Testing Methods
Sample Preparation and Initial Inspection
Testing is performed on a complete appliance or on representative specimens bearing production-intent markings applied to the same substrate with the same printing process and adhesive system. Specimens are conditioned under normal laboratory ambient conditions before testing. An initial inspection confirms that all required markings are present, correctly applied, and legible prior to any rubbing.
Water Rub Test
A soft, absorbent cloth is soaked in water and rubbed by hand over the marking surface for 15 seconds at moderate, uniform pressure in a back-and-forth motion. The cloth is re-moistened as necessary to keep the contact surface wet throughout the test. The marking is then inspected for smearing, fading, or ink transfer to the cloth.
Petroleum Spirit Rub Test
A fresh cloth is soaked in petroleum spirit, specified in the standard as aliphatic solvent hexane with an aromatics content not exceeding 0.1 percent by volume, an initial boiling point of approximately 65 °C, a dry point of approximately 69 °C, and a density of approximately 0.68 g/cm³. The marking is rubbed by hand with this cloth for 15 seconds. This stage is the most discriminating for solvent-based inks and marginal adhesive systems, and it is omitted for markings that are molded or engraved into the material under current editions of the standard.
Finger Rub Test
Where the applicable edition of the standard requires it, such as GB 4706.1 and earlier versions of IEC 60335-1, the marking is rubbed with the finger for 15 seconds immediately after the solvent exposure. This step evaluates the marking in its most vulnerable condition, when the ink or adhesive layer may be softened by the solvent, and simulates repeated manual contact with the marked surface.
Evaluation of Results
At the conclusion of the sequence, the marking is examined under normal lighting from the intended viewing distance. To pass, all characters and symbols must remain clearly legible, the nameplate must not be capable of easy removal, and no curling of label edges is permitted. Ink smearing, blurring, significant fading, delamination, or adhesive failure constitutes a non-conformity. As complementary development tools, manufacturers may also apply adhesion and abrasion methods from ASTM standards, such as tape adhesion or peel testing, to quantify margins of safety beyond the pass or fail criteria of the appliance safety standard.
Applications
Marking durability testing supports every stage of the appliance lifecycle, from design validation to market surveillance:
- Safety certification: the rubbing test forms part of the construction and marking assessment for national certification schemes, the IECEE CB Scheme based on IEC 60335-1, and regional market access programs referencing EN, GB, UL, or JIS adoptions.
- Design validation: engineers use the test to compare inks, label materials, adhesives, and surface treatments before production release, and to qualify laser etching or molding as higher-durability alternatives.
- Production quality control: routine in-house checks on nameplate batches and printed panels detect process drift, such as insufficient ink curing or contaminated bonding surfaces, before nonconforming product ships.
- Failure analysis: when markings fade or labels detach in the field, the standardized rubbing sequence helps laboratories identify root causes such as solvent-sensitive inks, low-grade adhesives, or inadequate substrate preparation.
- Regulatory oversight: market surveillance authorities use the same method to verify continued conformity of appliances already placed on the market.
Manufacturers preparing for certification typically engage accredited third-party laboratories to perform the test under the exact conditions of the applicable standard, ensuring that results are accepted without repetition during the conformity assessment process.
FAQ
Which standard clause governs marking durability for household appliances?
Clause 7.14 of IEC 60335-1, and the corresponding clause in EN 60335-1, GB 4706.1, UL 60335-1, and JIS C 9335-1, specifies that markings shall be durable and legible and defines the rubbing test with water and petroleum spirit used to verify compliance.
Are molded or engraved markings exempt from any part of the test?
Yes. Under current editions of IEC 60335-1, the petroleum spirit rub is not carried out on markings that are molded or engraved into the material, because these marking types are inherently resistant to solvent attack and abrasion.
How long does the test take?
The rubbing sequence itself requires only about one minute per marking, consisting of 15-second rubs with water, petroleum spirit, and, where applicable, the finger. Including sample preparation, conditioning, and evaluation, a full assessment is typically completed within a single laboratory session.
What are the most common failure modes?
Typical failures include ink smearing or dissolution during the petroleum spirit rub, label edge curling after solvent exposure, and complete detachment of adhesive nameplates. Effective remedies include solvent-resistant ink systems, higher-grade pressure-sensitive adhesives, thorough surface cleaning before label application, or switching to engraved and laser-etched markings.
Can the test be performed in-house?
Yes, the equipment is simple, consisting of absorbent cloth, water, aliphatic solvent hexane, and a timer, so manufacturers routinely run the test for design verification and production control. For certification purposes, however, the test should be performed by accredited third-party laboratories whose results are recognized by certification bodies and regulatory authorities.
Which products fall within the scope of the test?
All household and similar electrical appliances covered by the IEC 60335 series are in scope, including refrigerators, washing machines, dishwashers, cookers, microwave ovens, room heaters, fans, and personal care appliances, along with their associated marking components such as rating plates and warning labels.