IEC 61537 is a crucial international standard established by the International Electrotechnical Commission (IEC). The Chinese national standard GB/T 21762 adopts this standard equivalently. Focusing on the technical aspects of cable tray systems, IEC 61537 outlines strict requirements and regulatory guidelines for various technical indicators. The primary goal is to ensure the safety and stability of cable trays during electrical system operations, minimizing risks arising from tray failures and ensuring the reliable operation of electrical facilities.
When obtaining CE certification for cable trays, IEC 61537 serves as a critical reference. Adhering to this standard during production and certification helps cable tray products gain recognition in European markets, enhancing their competitiveness on the international stage. This drives the industry toward greater standardization and internationalization.
When selecting cable trays, enterprises often prioritize performance metrics, particularly safe working load. But how are these safe working load data determined? How are the tests conducted, and what does IEC 61537 specify?
In IEC 61537, safe working load is discussed under Chapter 10: Mechanical Properties. Two critical concepts are introduced:
Safe Working Load (SWL):
In the context of IEC 61537, “load-bearing” is formally referred to as SWL, which stands for “Safe Working Load.” SWL represents the maximum load that can be safely applied under normal operating conditions.
Uniformly Distributed Load (UDL):
The standard requires that load-bearing tests be conducted with a UDL, meaning the load must be applied uniformly across the tray.
Key Testing Principles of IEC 61537
IEC 61537 does not specify exact load-bearing values for cable trays. Instead, it defines a standardized load-testing methodology and provides the following evaluation criteria:
- Longitudinal deflection: less than 1/100 of the span.
- Lateral deflection: less than 1/20 of the width.
The SWL is the load applied to the tray when its deformation reaches these specified limits. Conversely, this method can also verify the load-bearing capacity of a tray.
The SWL testing procedures are divided into two categories:
General Procedure:
Includes both high- and low-temperature testing.
Special Procedure:
If the material of the cable tray has mechanical properties that do not vary by more than ±5% due to temperature changes within a certain range (e.g., steel), the SWL test can be conducted at any temperature.
SWL Testing: Single-Span vs. Multi-Span Configurations
SWL (Safe Working Load) testing involves two main configurations: single-span testing and multi-span testing. For clarity, this guide will focus on single-span testing as an example. The fundamental principles, however, remain consistent across both configurations.
1. Sample Placement
In a single-span setup, the sample cable tray is positioned with specific parameters and components, as follows:
- Cantilever Length: Represented as “1,” the cantilever length must not exceed 500 mm.
- Joints: Points of connection in the tray, labeled as “2.”
- Span (L): The distance between two supports, denoted as “3.”
- Local Weak Points: Identified as “4,” these are areas prone to deformation or failure.
- Support Positions (a/b): Represent the rigid supports on the same horizontal plane, with a width of 45 mm ± 5 mm.
Notes for the Setup:
- The supports labeled “a” and “b” ensure the tray remains rigid and stable during testing.
- The maximum cantilever length is restricted to 500 mm to ensure accuracy and consistency in the testing procedure.
- The specified dimensions and support configurations align with IEC 61537 requirements, providing a controlled environment to assess the tray’s performance.
2. Preloading and Baseline Adjustment
For the test sample, apply 10% of the Safe Working Load (SWL)as a preload. Maintain the load for 5 minutes ± 30 seconds, then remove it. At this point, adjust the measuring instruments to zero.
3. Incremental Loading
Gradually increase the load in both the horizontal and vertical directions until the SWL is reached.
- Note: Each incremental load must not exceed 1/4 of the SWL.
- The applied load must meet the requirement for Uniformly Distributed Load (UDL).
To achieve a UDL, a small tool called loading blocks is used. These blocks should be placed evenly across the width and length of the tray according to the standard. Placement should follow the guidance provided in two tables:
- Placement along the width direction, based on the width of the test sample.
- Placement along the length direction, based on the span of the cable tray.
4. Measuring Deformation Values
Two key deformation values need to be measured:
- Longitudinal Deviation (Span Center Deviation): The arithmetic mean of the deviations measured at two points near the side edges of the tray.
- Lateral Deviation: The difference between the third reading (taken at the center of the bottom of the cable tray span) and the span center deviation value.
5. Reading Measurements
Keep the test sample in its loaded state and take deviation measurements every 5 minutes ± 30 seconds. Continue this process until the difference between two consecutive sets of readings is less than 2% of the first reading in the first set. This first reading at this point is recorded as the deviation value under the SWL.
