The internal arc test, as defined within the scope of standards like IEC 61439, is a critical safety evaluation performed on electrical equipment, specifically low-voltage switchgear and controlgear assemblies (often referred to as LV Assemblies). Its primary goal is to determine the level of protection offered to personnel – both operators and ordinary persons – in the event of an internal electrical fault known as an arc fault.
Understanding Internal Arc Tests
An internal arc fault occurs when a sudden, high-energy discharge of electricity happens between conductors inside the equipment. This event is typically triggered by factors like insulation failure, foreign objects, or poor connections. The resulting arc generates intense heat, pressure, and harmful byproducts, posing significant danger to personnel and potentially causing extensive damage.
Purpose According to IEC 61439
Based on the provided reference, internal arc tests determine the level of protection of the test equipment against the operator and / or ordinary persons by checking internal faults that may occur in electrical equipment. The tests evaluate several key aspects:
- Personnel Protection: Ensuring that the effects of an internal arc fault are contained within the enclosure to protect individuals standing nearby from thermal effects, pressure waves, ejected parts, and fire.
- Equipment Integrity: Checking whether they protect the integrity of the equipment. This means verifying that the enclosure remains substantially intact and prevents the arc effects from spreading dangerously.
- Environmental Impact: Assessing whether the fault event causes excessive damage [to] the external environment, such as igniting surrounding materials or releasing toxic fumes uncontrollably.
Assessment Criteria
While detailed criteria are extensive within the standard, a successful internal arc test generally requires the equipment to prevent:
- Doors or covers from opening or being blown off.
- Solid parts from being ejected from the enclosure.
- Ignition of indicators or flammable materials near the enclosure.
- Burning through the external walls of the enclosure.
These criteria ensure that the assembly effectively contains the dangerous energy released during the arc fault.
Protection Levels (IAC-A and IAC-B)
The reference explicitly states that the protection level determined by these tests is classified into two types, IAC-A and IAC-B. These levels relate to the areas around the equipment where personnel safety is assessed. While the reference doesn't detail the distinction, generally in the context of such standards:
| Level | Description | Typical Personnel Area Covered |
|---|---|---|
| IAC-A | Internal Arc Classified - Access Limited | Protection primarily for authorized operators working directly in front of the equipment (e.g., operating cubicles, near doors). |
| IAC-B | Internal Arc Classified - Access Unrestricted | Protection for ordinary persons having free access to the general area where the equipment is installed (e.g., behind cubicles, sides, top, depending on installation). |
The specific required level (IAC-A or IAC-B) depends on the intended installation location and how personnel are expected to interact with or be present around the equipment.
Why Internal Arc Testing is Crucial
Internal arc testing is fundamental to the safety design of low-voltage switchgear and controlgear assemblies. By simulating a potentially catastrophic event under controlled conditions, manufacturers can validate that their equipment provides the necessary containment and protection to prevent injury or death in real-world fault situations. It's a vital part of ensuring the safety of electrical installations and the personnel who work near them.
