IEEE 1584-2018 Arc Flash Assessment — The Practitioner's Workflow

What Changed in 2018

The IEEE 1584-2018 edition replaced the 2002 model entirely. Key changes:

New empirical model based on 1,800+ arc flash tests (vs ~300 in 2002)
Expanded voltage range: 208V–15kV (was 208V–15kV but with a completely different formula)
Enclosure size and configuration now affect the result
Electrode configuration (VCB, VCBB, HCB, VOA, HOA) is a required input
Arc current variation factor replaces the old 85% multiplier

Step-by-Step Workflow

Step 1: Data Collection

For each equipment location, gather:

Voltage (line-to-line, nominal)
Bolted fault current (from short circuit study, in kA)
Gap between conductors (mm, from equipment documentation)
Working distance (mm, per NFPA 70E Table 130.7(C)(15)(a))
Enclosure dimensions (height, width, depth in mm)
Electrode configuration: VCB (vertical in box), VCBB (vertical in box with barrier), HCB (horizontal in box), VOA (vertical open air), HOA (horizontal open air)
Protective device clearing time at the arcing current

Step 2: Calculate Arcing Current

IEEE 1584-2018 uses a multi-variable regression model:

For 600V–2,700V: log(Iarc) = f(log(Ibf), log(V), log(gap))

The model produces an intermediate arcing current. Apply the arc current variation factor (VarCf) to get minimum arcing current — this is used to find maximum clearing time.

Step 3: Determine Clearing Time

Plot the arcing current (BOTH the calculated value AND the reduced value from VarCf) on the protective device time-current curve. Use the longer clearing time of the two — this gives the worst-case incident energy.

Critical: use the total clearing time including relay time + breaker operating time. Typical values:

MCB/MCCB instantaneous: 8–16ms
MCCB short-time delay: 100–500ms
MV relay + breaker: 50–100ms

Step 4: Calculate Incident Energy

The 2018 model:

E = f(Iarc, t, d, gap, electrode_config, enclosure_size)

Incident energy E is in cal/cm² at the working distance d.

Step 5: Determine Arc Flash Boundary

The arc flash boundary (AFB) is the distance at which incident energy equals 1.2 cal/cm² (threshold for second-degree burn onset). Solve the incident energy equation for distance.

Step 6: Select PPE Category

Per NFPA 70E Table 130.7(C)(15)(c):

Incident Energy (cal/cm²)	PPE Category	Minimum Arc Rating
0 – 1.2	Cat 0	Untreated cotton
1.2 – 4	Cat 1	4 cal/cm²
4 – 8	Cat 2	8 cal/cm²
8 – 25	Cat 3	25 cal/cm²
25 – 40	Cat 4	40 cal/cm²
>40	Exceeds PPE	Do not work energised

Step 7: Label Equipment

NFPA 70E 130.5(H) requires arc flash labels on equipment with:

Nominal voltage
Arc flash boundary
Available incident energy at working distance, OR PPE category
Date of assessment

Key Pitfalls

Using 2002 model inputs in 2018 model — the models are incompatible
Ignoring electrode configuration — VCB vs HCB can change incident energy by 2×
Not checking reduced arcing current — lower arc current = longer clearing time = potentially higher energy
Assuming instantaneous trip when the device is set to short-time delay

Run the assessment: Full IEEE 1584-2018 calculations in the Arc Flash Calculator.

Frequently Asked Questions

What is arc flash hazard?

Arc flash is an explosive release of energy during an electrical fault, creating temperatures exceeding 19,000°C. IEEE 1584-2018 provides calculation methods to determine incident energy and safe working distances.

When is arc flash assessment required?

NFPA 70E requires arc flash labeling on all equipment >50V that may require examination, adjustment, or servicing while energized. This includes switchboards, panelboards, and MCCs.

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