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Arc Flash Energy Calculations: What is it and when is it mandatory?

An arc flash is one of the most dangerous situations in electrical engineering and can lead to severe burns, permanent injury, or even fatal accidents. In this blog post, we explain what arc flash energy is, how to choose the right PPE, and whether these calculations are mandatory.

An arc flash energy calculation essentially determines how much energy can be released during an arc flash, which is crucial for selecting the correct class of personal protective equipment (PPE). This PPE comes in various classes and categories and protects up to a certain amount of energy. Therefore, you need to understand the maximum amount of energy that can be released to choose the correct category of PPE. And, in some cases, the energy is so great that no PPE can help.

What is Arc Flash Energy?

An arc flash is an explosive discharge of electrical energy through the air when insulation or separation between live conductors fails. This can happen due to:

  • Short circuits between phases or phase and ground
  • Incorrect use of tools in a switch cabinet
  • Dust or moisture in electrical panels
  • Aging or damaged equipment
  • Human error during maintenance

The energy released during an arc flash can reach extremely high temperatures, and the consequences can be catastrophic. Additionally, there are other consequences such as:

  • Thermal energy: Severe burns within milliseconds
  • Pressure wave: Can throw people and cause hearing damage
  • Flash of light: Can cause permanent eye damage
  • Molten metal particles: Splatter in all directions
  • Toxic gases: Created by the vaporization/combustion of materials

Realistic Electrical Arc Flash

PPE Categories

  • Category 0: < 1.2 cal/cm² - Non-melting clothing
  • Category 1: 1.2 - 4 cal/cm² - Arc-rated clothing 4 cal/cm²
  • Category 2: 4 - 8 cal/cm² - Arc-rated clothing 8 cal/cm²
  • Category 3: 8 - 25 cal/cm² - Arc-rated clothing 25 cal/cm²
  • Category 4: 25 - 40 cal/cm² - Arc-rated clothing 40 cal/cm²
  • Category 4+: > 40 cal/cm² - Live working not permitted

Insulating Gloves

  • Class 00: Max 500V AC
  • Class 0: Max 1,000V AC
  • Class 1: Max 7,500V AC
  • Class 2: Max 17,000V AC
  • Class 3: Max 26,500V AC
  • Class 4: Max 36,000V AC

NEN 3140 - Table 106

For low-voltage installations, which fall under NEN 3140, it is indicated that such calculations are necessary if installation parts are protected with circuit breakers larger than 80A or with fuses larger than 630A. This can be read from Table 106 of this standard. Note that NEN 3140 applies to low-voltage installations.

If the protection is implemented with a circuit breaker up to 80A or up to 630A blade fuses, the PPE can be chosen based on Annex G of NEN 3140. This annex deals with the distance to touchable live parts and the height of the protection. Based on this annex, you can determine which class of PPE you should use in which cases. These are normally designed in Class 0 (up to 1000VAC).

Risk Analysis

A risk analysis will need to show whether an arc flash energy calculation should be performed. After all, you determine the PPE class based on the amount of energy that can be released, and the PPE must be suitable for that. Formally speaking, you must first clarify the amount of energy released, and only then can you determine the correct class/category of PPE. However, we have not been able to find a legal obligation for such calculations in legislation and standards, so the risk analysis will have to provide a solution; insurers can, of course, also demand this.

Richard Winter

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