[1] An arc fault is a a type of electric fault, a hazardous electric explosion and discharge through the air. It releases blinding light and extreme heat reaching up to 35,000°F. Specialized personal protective equipment (PPE) shields workers from severe thermal burns and blast impacts.
A lamp cord extension run under a desk.
What happens if the chair rolls on the cord repeatedly.
It'll damage the insulation. But if lucky, only a short occurs and blow the fuse.
But if it arcs:
it draws less current than a short
It takes longer to clear
Arc faults then causes fire to start.
Current outside the normal current path.
Current maybe under normal levels or above high levels.
Heat is concentrated in a very small area.
Current changes rapidly during the fault.
Line to neutral
This could be what occurred
under the desk.
Worst case: not enough current to trip the breaker or it
takes a long time to trip.
If the arc draws 10 amps at 120 volts you have 1200 W in a small space.
Line to ground
What if the grounding (bonding) path has high resistance?
Not enough current to trip the breaker or it takes a long time to trip.
What does this say about how we should bond?
Line to line
With big 3-phase systems the amount of energy unleashed by an arcing fault is huge.
These are often 3 phase line-to-line faults.
Line to series
If a circuit opens under load, current may continue to flow by arcing.
This can be a conductor breaking or a switch failing to fully open.
Here, current is limited by the load.
Why is limited current a problem?
These are all parallel arc-faults:
26-650 Special terminology
In this Subsection, the following definitions apply:
Arc-fault protection a means of recognizing characteristics unique to both series and parallel arc-faults and de-energizing the circuit when an arc-fault is detected.
Aside from sudden blast and balance loss causing secondary injuries, like falls from heights or blunt, or extreme temperature of up to 19,000°C causing 3rd degree burns, the following are other dangers and phenomena arc faults can cause.
A bolted/solid fault is a solidly connected fault path or short-circuit condition where current flows through a low-resistance physical connection between phase conductors or phase conductors and grounds. It's also the energy dissipated in faulted equipment
An arc flash is the thermal energy the intense heat and light created by the electric arc. Temperatures can reach up to 35,000°F, causing severe burns, ignites clothing, and instantly melts or vaporizes nearby metal components. Even yards away via IR radiation can be a hazard.
An arc blast is the fast air expansion (explosion) and metal plasma creates a violent pressure wave capable of rupturing eardrums (exceeding 140 decibels), knocking workers off ladders, or collapsing structural building elements.
Projectiles and molten metal: Copper and steel components vaporize and violently eject as liquid metal droplets and high-speed shrapnel travelling at speeds up to many hundred miles per hour, piercing ordinary garments and penetrating eyes or skin.
Intense optical radiation: A blinding flash of ultraviolet (UV) and infrared (IR) light can cause temporary or permanent vision impairment, corneal damage (arc eye), and retinal burns.
Toxic gases and byproducts: The combustion of wire insulation, plastics, and vaporized metals produces hazardous, toxic clouds of chemicals and metal fumes that can cause severe lung and respiratory damage.
Combination-type arc-fault circuit interrupter is a device giving both series and parallel arc-fault
protection to the whole branch circuit wiring, including cord sets and power supply cords connected to
the outlets, against unwanted arcing effects.
the arc fault sensing circuitry
The neutral conductor
The neutral terminal
Outlet branch-circuit-type arc-fault circuit interrupter — a device that provides both series and parallel arc-fault protection to downstream branch circuit wiring, cord sets, and power supply cords against the unwanted effects of arcing and also provides series arc-fault protection to upstream branch circuit wiring.
Arc faults are detected by fasting changing current.
Vacuum cleaners' motors and similar appliances have brushes that arc sometimes causing false tripping.
The arc flash boundary is the closest safe distance one can stand to energized electrical equipment without wearing special protective gear. At this distance, the thermal energy from an unexpected electric arc drops to 1.2 calories per square centimeter (cal/cm2), which is the threshold for a second-degree burn on unprotected skin.
[D1] determines distance from equipment at which an arc flash's incident energy is 1.2 cal/cm2.
[D1] Limited/Restricted/Prohibited approach boundary are defined by voltage.
"Racking" is the process of physically inserting/withdrawing a draw-out circuit breaker from its connected switchgear busbars, one of the most dangerous electrical tasks because mechanical friction, misalignment, or component failure can spark a high-energy arc flash or arc blast directly in front of the operator.
Remote racking eliminates human exposure by removing the worker from the arc flash boundary. IO an electrician manually turning a crank while standing right at the panel door, a motor mechanism performs the motion while the operator controls it from a safe distance.
IEEE 1584 is the industry-standard guide by the Institute of Electrical and Electronics Engineers (IEEE) to calculate arc-flash hazard boundaries and incident energy levels, providing mathematical formulas to evaluate thermal risk, select proper personal protective equipment (PPE), and set safe working distances for electrical workers.
[D1]
IEEE 1584 configurations are 5 distinct electrode and bus arrangements defined in the IEEE 1584 standard to calculate arc flash incident energy. These configurations model how an electric arc behaves based on conductor orientation, enclosure presence, and barriers.
A box configuration is one of the two configurations of the IEEE 1584 and refers to energy channeled in 1 direction. 3 of the IEEE 1584 configurations are box configurations:
VCB (vertical conductors in a box) consists of vertical bus bars housed in a metal enclosure. It represents the standard baseline for most typical indoor electrical equipment, such as general panelboards, lighting panels, and traditional switchgear. Since the box's metal walls restrict the arc blast from expanding sideways or backward, the energy is forced out of the open front, resulting in a medium-to-high incident energy impact focused directly toward the worker.
VCBB (vertical conductors with a barrier in a box) refers to vertical conductors that terminate into an insulating barrier or block (such as a molded-case circuit breaker). The barrier reflects and directs the plasma cloud forward, increasing incident energy.
HCB (horizontal conductors in a box) refers to horizontal bus bars in an enclosure. This often represents configurations like motor control center (MCC) stabs where energy projects outward toward a worker.
An open configuration refers to energy released in all direction. 2 of the IEEE 1584 configuration are open configurations:
VOA (vertical conductors in open air) refers to vertical electrodes without an surrounding enclosure, representing outdoor substation or open bus setups.
HOA (horizontal conductors in open air) refers to horizontal electrodes without an enclosure, representing open-air horizontal bus arrangements.
Arc flash equipments are special personal protective gear and safety tools that protect workers from intense thermal energy, blast pressure, and electrical shock. This gear ranges from standard flame-resistant (FR) daily wear to full-body 100 cal/cm² suits and insulated safety devices.
Arc flash PPEs (personal protective equipment) are types of arc flash equipments that are wearable that are flame-resistant gear worn by electrical workers to block thermal energy, avoid severe skin ignition, and limit burn injuries to a survivable second-degree threshold in an unexpected electric arc flash explosion.
Arc flash PPEs are split into 4 types under NFPA 70E and CSA Z462 standards.
Althought, CSA Z462 recently added a 5th category with potential incident energy levels up to 75 cal/cm2.
Category 1 (4 cal/cm2)
Category 2 (8 cal/cm2)
Category 3 (25 cal/cm2)
Category 4 (40 cal/cm2)
Each step up requires higher thermal protection, moving from single-layer shirts and face shields to heavy multi-layer full-body flash suits.
[2]
[2] In Canada, which the CSA Z462 group standard are used to determine appropriate PPE.
[2] Why the Category 5 arc flash PPE was added Arc flash thermal incident energy is calculated via the IEEE 1584 guide's engineering formulas. Regardless how a client did their arc flash risk assessment (incident energy analysis/category method), arc flash PPE selection is determined via such calculations. Hidden behind each Arc Flash PPE Category are incident energy calculations based on the equipment parameters from CSA Z462 Table 6a. If the IEEE 1584 guide was updated in 2018, the new formulas resulted in significant changes. E.g., 600 V switchgear in Table 6a increased from 40 cal/cm2 up to 73 cal/cm2. The basic principle of arc flash PPE selection is the protection (arc rating) must match or exceed the hazard. Up until now, 600 V switchgear required Category 4 protection with a minimum arc rating of 40 cal/cm2. So the CSA Z462 Standard needed a higher category to ensure workers were adequately protected. Arc Flash PPE Category 5 requires a min. 75 cal/cm2 arc rating that can provide adequate protection for this example.
Aside from wearable PPE, these are non-wearable arc flash equipment:
A hotstick is a insulated rescue hooks or long non-conductive fiberglass poles used to pull an injured worker away from an active energized hazard without putting the responder at risk.
Pliers, screwdrivers, and wrenches rated up to 1 kV to prevent accidental shorts across live terminals.
Static/Capacitor Discharge Sticks: Grounding rods used to safely dissipate residual voltage from capacitors or de-energized lines before contact.
[D2]
[D3]