Arc-Flash Relay

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The AF0500 is a microprocessor-based arc-flash relay that limits arc-fault damage by detecting the light from an arc flash and rapidly tripping the feeder breaker. The unit is well suited for switchgear, transformer and power converter applications.

Sensors, inputs, and connections are health monitored to ensure fail-safe operation. A secondary solid-state trip circuit provides a redundant trip path. A USB port is used for configuration and access to event logs.

AF0500 includes an Ethernet interface and supports Modbus® TCP communication. Zone tripping, upstream breaker tripping and tie breaker tripping applications can be easily configured.

A number of control inputs allows interconnection of multiple AF0500 units to form a system.

Arc-Flash Detection and Response in less than 1ms 

Arc-Flash Relay saved a plant from catastrophic damage  

Optical Sensors

The AF0500 accepts both PGA-LS10 point sensors and PGA-LS20/PGA-LS30 fiber-optical sensors. Thus any combination of fiber or point sensors is supported.

For fast fault location, front-panel and sensor LEDs indicate sensor health and which sensor detected an arc fault.

Sensor Placement

The AF0500 Arc-Flash Relay and sensors are easily installed in retrofit projects and new switchgear with little or no re-configuration. Simple applications work straight out of the box with no need of PC configuration. More complex systems with multiple power sources are configured using the relay’s built-in USB interface software.

Generally, it is recommended to mount 1 or 2 sensors per cubicle to cover all horizontal and vertical bus bars, breaker compartments, drawers, and anywhere that there is a risk for an arc fault. Threading a fiber-optic sensor through the cabinets and in areas where point-sensor coverage is uncertain results in complete coverage and an added level of redundancy. Even if policy is to only work on de-energized systems, all maintenance areas should be monitored to prevent potential damage and additional cost. 

Features & Benefits

  • 4 arc sensor inputs

    Supports both point and fiber sensors

  • Arc-Flash trip time <1ms

    Limits arc-flash damage and risk of injury

  • 2 IGBT high speed trip outputs

    Supports applications such as upstream breaker tripping or tie breaker tripping

  • Universal Power Supply

    100-240 Vac, 24-48 Vdc, or 110-250 VDC supply

  • Fail-safe system

    Continuous monitoring of optical sensors and inputs ensures protection

  • LED indication (on unit and each sensor)

    Trip and sensor status indicated both on relay and sensors

  • Discrete wire networking

    Multiple AF0500 units can be interconnected to form a system

  • USB interface

    Data logging and configuration software uses a USB interface with no drivers or software installation

  • Data logging

    On-board event recorder for system diagnostics (2048 log lines)

  • Ethernet interface

    Modbus® TCP communication

AF0500 Datasheet

AF0500 Manual

Littelfuse Arc-Flash Relay Brochure

AF0500 Arc-Flash Relay Application Guide

Littelfuse Arc Flash Energy Reduction Workbook


Power Supply 

  • Universal: 100 to 240 VAC (+10%, -15%) 50/60 Hz, 20 VA,110 to 250 VDC (+10%, -20%) 8 W
  • Low Voltage: 24 to 48 VDC (+10%, -20%), 4 W
  • Sensor Inputs: 4 light sensor inputs for PGA-LS10, PGA-LS20 and PGA-LS30 sensors
  • Trip Outputs: 2 IGBT switches
  • UL Rating: 120/240 Vac, 1800 VA, 0.75 A maximum continuous, 125/250 Vdc, 138 VA, 0.75 A maximum continuous

Supplemental Rating

  • Make/Carry: 30 A for 0.2s
  • Voltage Rating: 24 to 300 Vac, 24 to 300 VDC
  • Current Rating: 20 A for 2 s, 10 A for 5 s
  • Communication: Ethernet, 2 ports with internal Ethernet switch, Modbus® TCP
  • Dimensions: H 130 mm (5.1”); W 200 mm (7.9”); D 54 mm (2.1”)
  • Shipping Weight: 0.9 kg (2 lb)
  • Operating Temp.: –40°C to +70°C (–40°F to 158°F)
  • Approvals: UL Listed (UL508), CE, RCM, FCC, CSA
  • Warranty: 5 years
  • Mounting: Surface, DIN (with optional D0050 adapter clips)

Ordering Information

AF0500-00 Arc-Flash Relay
AF0500-00-CCArc-Flash Relay, Conformally Coated
PGA-LS20, PGA-LS30 Required*


PGA-LS10 Point Sensor
Line-of-sight light sensor detects an arc as small as 3 kA within a 2-m half-sphere. Includes Sensor health and trip indication.

PGA-LS20/PGA-LS30 Fiber-Optic Sensor
360° light sensor to run along bus bars. Sensor health and trip indication.

PGA-1100 Diode Logic Unit
This module allows multiple arc-flash relays to trip a common breaker, for example a tie-breaker.


How Do Arc Flash Relays Work?

Featured Case Study

Littelfuse Arc-Flash Relay Saves Plant from Catastrophic Damage

Tim Deschamp from Evans Enterprises, Tulsa, Oklahoma, was working with a customer to help them resolve and reduce a critical issue with an electrical hazard in their furnace control room. An earlier arc-flash analysis had determined that one 480-volt cabinet, which was fed from a 3500 kVA transformer, exceeded an arc-flash Hazard Risk Category 4 (HRC).

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Top FAQs

A protection relay is a device that receives inputs typically from current transformers CT’s (but can be other sources) and then compares these inputs to set levels. If these inputs exceed the set levels a protection relay can then provide that information via display or indication, feed that information to other electronic control devices or it can be connected to a circuit breaker to isolate power.

Yes, currently Fuseco can offer both earth leakage and NER relays that are compliant to AS2081:2011. The relay manufacturer (Littelfuse) is also currently in the final stages of development for an AS2081:2011 compliant continuity relay that we expect to release in the near term.

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 degrees, and a resulting explosive pressure wave (arc blast). By using a relay that has optical sensors we can detect the flash of light the emanates from an Arc Flash and within 1 msec send a signal to a breaker to interrupt power. Because of the immense energy being released by an Arc Flash reaction time is critical. It can be seen on the graph that with a relay reaction time of only 1 msec (+ circuit breaker reaction time) we can interrupt power before the Arc Flash can result in critical damage.

An arc-flash happens when electric current flows through an air gap between conductors. There are several ways this can happen but the most common occurrence is when conductor insulation is worn or broken down.

The most important aspects of arc-flash relays are:

  • reaction time
  • trip reliability
  • ease of installation
  • sensor flexibility
  • software
  • sensor design
  • avoidance of nuisance tripping
  • scalability

To gain a deeper understanding of which features to consider when selecting an arc-flash relay please refer to the downloadable application guides.

Arc-flash relays are a necessary component in an electrical cabinet because they reduce the amount of incident energy in the system. 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. An arc-flash relay is an integral part of an arc-flash protection scheme that can minimize damage, and save money, time, and lives.

Three phase power systems are most often solidly earthed, however by using a Neutral Earthing Resistor (NER) a power system can be resistance earthed. This is done so that if an earth fault were to occur the amount of fault current will be limited by the NER resistance. One potential problem with a resistance earthed system is; what happens if the NER goes open circuit due to damage? If this were to happen the power system has now changed from a resistance earthed system to a system with no earth reference (floating). Now the NER is no longer restricting the amount of fault current and other devices that rely on an earth reference in order to operate, cannot do so. By using a NER monitoring relay the resistance and integrity of a NER can be continually monitored to detect for any variance in the NER resistance or integrity.

An earth fault can occur as a result of inadvertent contact between and energized conductor and earth or equipment frame. There can also be earth leakage from a system without “inadvertent contact”. This type of fault can be called capacitive earth leakage and it is caused by a capacitive effect between a high power conductor and earth. Small amount of earth leakage current can occur as a result of this capacitive effect. Whether it is smaller amounts current from capacitive earth leakage or larger amounts of current from direct inadvertent contact an earth leakage relay can detect this fault current. In all electrical circuits, current returns to its source. An earth fault relay can use a zero sequence CT to monitor phase current to ensure that all current coming from the source returns on those same conductors or it can monitor current in the connection between transformer neutral and earth. By either method the earth leakage relay detect any lost current to earth.

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Applicable Industries

Hi Tim, just wanted to thank you and the Fuseco team for your help. You've managed to help us solve some nagging issues here and the Littelfuse SE-330AU relay installation has saved us a lot of time. Thanks!

Mark Sherman

PGS Silver, Queensland

Just wanted to send a note of thanks to you guys. When it comes to relays, your advice & service is high level & appreciated. Cheers.

Jesse Marshall

Newcrest WA

The Littelfuse SE-701 & the CT's are functioning well. Thanks guys, really appreciate your help. Good to work with people you can rely on.

Cliff Peligro

Alpha Coal, Queensland

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