You probably already know that ratings such as IP65 and IP67 indicate how well an enclosure protects against dust and water. But what about ratings that include additional letters, such as IP20B, IP2XD or IPX4W?
While these classifications don't appear on every product, they're used across a wide range of industries to provide additional information about how equipment has been tested and where it can be used safely and effectively.
In this guide, we'll explain what these letters mean, where they appear within AS 60529, and why understanding them can help you make more informed compliance, design, and specification decisions.
Key Takeaways
- Additional and supplementary letters in AS 60529 provide important information that standard ingress protection ratings cannot communicate on their own.
- Letters such as A, B, C and D indicate protection against access to hazardous parts, while H, M, S and W provide additional context about equipment type or testing conditions.
- Working with an experienced ingress protection testing provider can help ensure your product is assessed against all relevant AS 60529 requirements.
Understanding the Structure of an AS 60529 IP Rating
The AS 60529 standard is Australia’s adoption of the internationally recognised IEC 60529 Ingress Protection (IP) framework. It defines how electrical enclosures are tested and classified for protection against solid objects, dust, water, and access to hazardous parts.
Most people are familiar with the two-number format:
- First numeral = protection against solid objects and dust
- Second numeral = protection against water
For example, an IP65 rating indicates a dust-tight enclosure that is also protected against water jets.
However, AS 60529 also allows optional letters to be added after these numerals when further information is needed.
A typical format may look like: IP 2 3 C H
Where:
- IP = Ingress Protection
- 2 = protection against solid objects
- 3 = protection against water
- C = additional letter
- H = supplementary letter
If a characteristic numeral is not specified, it’s replaced with the letter "X". This is why you may see classifications such as IPX4 or IP2XD.
Additional Letters (A-D): Protection Against Access to Hazardous Parts
In IP certification, additional letters focus on human safety. They are used to indicate the level of protection provided against access to hazardous internal components using standardised test probes.
While the first IP numeral already provides a degree of protection against accidental contact by restricting access through the enclosure, some products require more specific information about how well hazardous parts are protected. Additional letters help provide that extra level of detail.
A – Back of Hand Protection
The letter A indicates protection against access using the back of a hand. This classification confirms that hazardous parts cannot be reached by a large IP test probe, thereby preventing accidental contact with a hand.
B – Finger Protection
The letter B indicates protection against access using a standardised test finger. An ingress protection rating like IP20B demonstrates that a person cannot reach hazardous parts with a finger under the specified test conditions.
C – Tool Protection
The letter C indicates protection against access using a tool. The ingress protection test involves using a test probe designed to simulate common tools that could potentially enter openings in the product enclosure.
D – Wire Protection
The letter D represents the highest level of access protection within this classification system. The ingress protection test is performed using a fine wire probe to confirm that hazardous parts remain inaccessible even through very small openings.
Supplementary Letters (H, M, S and W): Additional Testing Information
In IP certification, supplementary letters provide extra information about the equipment itself or the conditions under which an ingress protection test was performed.
H – High-Voltage Apparatus
The letter H identifies equipment intended for high-voltage applications. It’s used where the relevant product standard requires this additional designation.
M – Equipment Moving During Water Testing
The letter M indicates that the movable parts of the equipment were operating during water ingress testing. Examples may include rotating machinery, fans, or motors where movement could influence water ingress behaviour.
M – Equipment Stationary During Water Testing
The letter S indicates that movable parts were stationary during water testing. This designation helps clarify the exact conditions under which the ingress protection rating was achieved.
W – Weather Conditions
The letter W identifies equipment designed for use in specified weather conditions and provided with additional protective features or processes. This supplementary letter is often relevant for products intended for challenging outdoor environments.
Why Do These Letters Matter?
For many products, a standard Ingress Protection (IP) rating provides all the information needed. However, in sectors such as defence, aerospace, energy, transportation, and industrial manufacturing, additional detail can be essential.
The optional letters defined within the AS 60529 standard help engineers, specifiers and compliance teams understand:
- Whether hazardous parts can be accessed through enclosure openings
- The specific conditions under which IP testing was performed
- Whether specialised operating or environmental factors have been considered
- How a product's protection characteristics align with industry-specific requirements
Without this additional context, important safety or compliance information may be overlooked.
What Is IP Testing?
Ingress Protection (IP) testing is the process used to verify an enclosure's ability to resist the entry of dust, water, solid objects and other external influences.
Depending on the required ingress protection rating, IP testing may involve:
- Dust chamber testing
- Water spray testing
- Immersion testing
- Access probe testing for hazardous parts
Common applications include verifying resistance to splashing water from any direction (IPX4 testing), confirming dust-tightness and resistance to low-pressure water jets (IP65 testing), and conducting IP test leak evaluations to identify potential ingress failures in seals or enclosures under stress.
Testing is typically performed by accredited, third-party test laboratories under controlled conditions to determine whether a product complies with the relevant requirements of AS 60529 and associated standards.
Partner with Austest for Accredited AS 60529 Testing
Understanding the additional and supplementary letters within AS 60529 standards is only one part of achieving compliance. Selecting the correct Ingress Protection (IP) rating, defining the required test programme, and obtaining reliable certification evidence all require specialist expertise.
At Austest Laboratories, we provide accredited IP testing services for product compliance programmes of all sizes and sectors.
Whether you're investigating a potential IP test leak issue, validating a new enclosure design, or preparing products for local and international markets, our professional and friendly team can help you navigate the AS 60529 standard with confidence.
Contact Austest today to map out a comprehensive AS 60529 ingress protection testing program for your product.
FAQs About IP Testing to AS 60529
Do all products require IP testing?
No. IP testing is only required where a product must demonstrate a specific level of protection against dust, water, solid objects or access to hazardous parts. Common examples include electrical enclosures, lighting, industrial equipment, telecommunications hardware, defence systems, and outdoor electronic products.
Who is responsible for determining the required IP rating?
This typically depends on the product and its intended application. Product designers, manufacturers, engineers, and compliance teams are usually responsible for identifying the appropriate ingress protection rating based on industry standards, operating environments and customer requirements.
What is the difference between an IP rating and an IK rating?
An Ingress Protection (IP) rating measures resistance to dust, water, and access to hazardous parts. An IK rating measures resistance to mechanical impact. While IP testing evaluates environmental protection, IK testing assesses how well an enclosure withstands physical impacts from external forces.
Why is third-party IP testing important?
Independent ingress protection testing provides objective evidence that a product meets the requirements of AS 60529 and other relevant standards. It also gives manufacturers, customers, and regulators confidence that testing has been carried out using recognised procedures and controlled conditions.
What happens during an ingress protection test?
The exact process depends on the required ingress protection rating. Testing may involve exposing products to dust chambers, water sprays, immersion tanks, impact tests, or access probes designed to simulate contact with hazardous internal components.
Can a product be tested for both IP and IK ratings?
Yes. Many products undergo both IP and IK testing, particularly those used in industrial, public-facing or outdoor environments. Together, these tests provide a more complete picture of an enclosure's ability to withstand environmental conditions and physical impacts.