Arc Flash Calculator

What this arc flash calculator actually does

This page is for a narrow but useful task: you already have a known incident-energy case or equipment-label value for the same equipment configuration, and you want to screen how that energy shifts when working distance or clearing time changes. It is not a fault-current-to-incident-energy engine and it does not replace an IEEE 1584 study.

What you enter

• Base incident energy: a known value such as an arc-flash study result or existing equipment label
• Base working distance: the distance tied to that known base case
• Target working distance: the new distance you want to screen
• Base clearing time: the protective-device clearing time tied to the known base case
• Target clearing time: the clearing time you want to compare against the base case

Screening assumption used on this page

The page uses a proportional screen:

Adjusted incident energy = base incident energy x (target clearing time / base clearing time) x (base distance / target distance)^2

That means the tool assumes the same equipment case, the same study basis, and an inverse-square distance relationship while clearing time changes in direct proportion. This is useful for fast comparison, but it is still only a screen built from a known case.

Worked screening example

If a known base case is 8.0 cal/cm2 at 18 in and 0.08 s, then moving the worker to 24 in at the same clearing time screens at about 4.5 cal/cm2. Under the same assumptions, the approximate 1.2 cal/cm2 boundary is about 46.5 in.

If the distance stays at 18 in but clearing time rises from 0.08 s to 0.20 s, the same base case screens at about 20 cal/cm2. That example shows why clearing-time changes can dominate the final energy even when the equipment itself stays the same.

Scope limits that matter

• This page does not calculate incident energy from available fault current, equipment type, conductor gap, or protective-device settings.
• This page does not assign an NFPA 70E PPE category.
• This page does not create labels or approve energized work.
• This page is useful only when the base incident-energy case is already known and still applies to the same equipment configuration.

The arc flash boundary shown here is the approximate distance where screened incident energy falls to 1.2 cal/cm2. NFPA 70E uses that 1.2 cal/cm2 level for the arc-flash boundary concept. NFPA 70E also requires arc-rated body protection with an arc rating not less than the estimated incident energy when exposure remains inside that boundary.

Use the Short Circuit Calculator when the real question is available fault current. Use the Protection Coordination Calculator when the real question is clearing time or device selectivity. Use a project study when you need actual IEEE 1584 incident-energy calculations, equipment labels, or energized-work decisions.