VOA Electrode Configuration: Vertical Conductors in Open Air

What VOA means physically

VOA stands for vertical conductors in open air: the conductors run vertically with no enclosure around them. Outdoor terminations, riser poles, open bus in switchyards, and cable terminations in open trays are the typical constructions. IEEE 1584-2018 defines VOA in Clause 4.3 (Table 9) as one of five electrode configurations — and it is the configuration where the "open air" half of the standard's five-model structure starts, because removing the box changes the plasma behavior as much as rotating the conductors does.

How VOA shapes the incident energy

With no enclosure, the arc energy radiates in all directions instead of being focused through an opening. The plasma still rises along the vertical conductors, but there are no walls to channel it toward the worker. Two consequences: the open-air configurations skip the enclosure-size correction factor entirely (there is no box to correct for), and at typical low-voltage inputs VOA computes the lowest incident energy of the five. Do not read "lowest" as "safe" — a long clearing time on a stiff source can still produce several cal/cm² in open air.

Engine-verified numbers at a common input set

At a common input set — 480 V, 25 kA bolted fault current, 32 mm gap, 455 mm (18 in) working distance, 200 ms clearing time — our calculator's engine computes for VOA: incident energy 4.49 cal/cm² and arc-flash boundary 40.9 in. The incident-energy selection basis is arc rating ≥4.49 cal/cm², not a category. Comparison at identical inputs: VCB 9.53, VCBB 13.25, HCB 19.51, and HOA 9.46 cal/cm².

When to select VOA in the calculator

Select VOA when the conductors at the work point run vertically and are genuinely in open air — not inside a cabinet, a junction box, or a weatherhead enclosure. Outdoor switchgear with the doors open is not automatically open air; if the arc would start inside the enclosure, the boxed configurations apply. Genuine open-air examples: pole-top terminations, padmount exteriors after the cover is removed (work point outside the box), and open bus runs.

Good to know: VOA's lower numbers are a geometry fact, not a hazard assessment. Open-air work adds exposure the calculation does not model — weather, approach distances for overhead lines, and falling-conductor risks. The incident-energy number answers one question; the risk assessment answers the rest.

Diagram

Diagram placeholder: vertical open-air termination on a riser, plasma rising along the conductors, worker position at 455 mm. Ships with the site diagram set; this page is text-complete without it.

The other four configurations

• VCB — vertical conductors in a metal box
• VCBB — vertical conductors terminated in an insulating barrier
• HCB — horizontal conductors in a metal box
• HOA — horizontal conductors in open air

Run the numbers for your own panel in the free arc flash calculator — electrode configuration is one of the inputs, and every intermediate value is shown for review. Related reading: arc flash boundary explained, PPE selection methods, and arc flash label requirements.