While an arc flash is sometimes used interchangeably with “arc fault”, an arc flash is more accurately defined as the light produced during an arc fault. An arc fault is a type of electrical fault that results from the breakdown of an insulating medium between two conductors where the energy is enough to sustain an arc across the insulator (often air) and can cause extreme amounts of light (arc flash), immense heat upwards of 19,000 °C, and a resulting explosive pressure wave (arc blast). このような力は、金属を気化し、機器を破損するなどして、近くにいる人を重大な危険にさらす危険な状態を生み出します。


アーク放電は、コンダクタ間のギャップに電流が流れることによって発生します。 There are several ways this can happen but the most common occurrence is when conductor insulation is worm or broken down.



How Do Arc-Flash Relays Work?

Video transcript:

There are many reasons an arc flash can occur and Littelfuse arc-flash relays can provide superior protection against its damaging results. Littelfuse market-leading arc-flash relay designs deliver reliable, easy-to-install protection. Littelfuse arc-flash relays and sensors are plug-and-play making them as easy to retrofit into existing switchgear as installing them into new equipment. No additional software is required.

Littelfuse arc-flash relays use light instead of current to detect an arc flash in under one millisecond. The fiber optic light sensor detects light throughout the entire length of the fiber. The sensor is ideal to protect buss bars, multiple compartment installations like motor control centers, or areas with many obstructions.

Littelfuse sensors are interchangeable. Giving the flexibility to adjust as needed during installation. The sensor's red flashing light tells you the sensor is installed correctly and working. This visual indication serves as a warning to workers; if they open a cabinet and there's no light they know to close it immediately. Littelfuse recommends mounting one or two sensors per cubicle to cover all horizontal and vertical buss bars, breaker compartments and anywhere there's potential for an arc flash. Littelfuse arc-flash relays have backup trip paths, so if one fails the other is still protecting.

Arc flash relays improve sustainability and life of electrical equipment. They can also help lower the PPE category of protected equipment. An arc-flash relay is an integral part of an arc-flash protection system that can minimize damage, save money, time and lives.

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Call our application experts at (800) 832-3873 to get more information.


アーク放電リレーは、システム内の入射エネルギーの量を減らすため、電気キャビネットに必要なコンポーネントです。 While an arc-flash relay cannot prevent an arc flash from happening, it will protect critical assets and workers' safety by reducing the severity of the flash.アーク放電リレーは、損害を最小化し、コストや時間を節約して命を守るアーク放電保護スキームに不可欠なコンポーネントです。


480 V のシステムにおける 20,000 アンペアの故障電流での相間故障には、9,600,000 ワットの力があります。 If there is no arc protection and the fault lasts for 200 milliseconds before the overcurrent protection clears it, then nearly 2 megajoules of energy will be released, which corresponds roughly to a stick of dynamite.

Energy = voltage × 電流 × 時間
480 V × 20,000 A × 0.2 s = 1,920,000 J

For a given system voltage, two factors can be adjusted to reduce arc-flash energy: time and current. Time can be reduced by using an arc-flash relay, such as the PGR-8800 or AF0500, to rapidly detect an electric arc flash. アーク放電リレーにより接続されている回路ブレーカーが瞬時にトリップし、反限時の遅延をオーバーライドします。電流は、限流ヒューズ、あるいは相接地短絡の発生に備える高抵抗接地を利用して抑えることができます。


The most important aspects of arc-flash relays are:

  • 反応時間
  • トリップの信頼性
  • 取付けの容易さ
  • センサーの柔軟性
  • ソフトウェア
  • センサーの設計
  • 不要なトリップの防止
  • 拡張性

Gain a deeper understanding of which features to consider when selecting an arc-flash relay with the white paper, Key Considerations to Selecting an Arc-Flash Relay.



アーク放電事象は危険なもので、人(作業者)の命に関わる恐れがあります。 According to OSHA, industrial arc-flash events cause about 80% of electrically-related incidents and fatalities among qualified electrical workers.作業員の怪我が避けられた場合でも、アーク放電は機器を破壊し、結果として機器の交換やダウンタイムによる損失を被るのは避けられません。

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