I know that most AF software only covers three phase systems, but is there any field experience with arc flashes on single phase 277V lighting circuits? Would OSHA consider a 277V arc flash a '[color="Red"]recognized hazard[/color]' under Section 5(a)(1)?

OSH Act of 1970
http://www.osha.gov/pls/oshaweb/owasrch.search_form?p_doc_type=OSHACT&p_toc_level=0&p_keyvalue=&p_status=CURRENT

SEC. 5. Duties
(a) Each employer --
(1) shall furnish to each of his employees employment and a place of employment which are free from [color="Red"]recognized hazards[/color] that are causing or are likely to cause death or serious physical harm to his employees;

I would say that it would need to be considered because it is 240 and greater, even if fed from less than 125KVA xfrm. Most of us are using the 3 phase equations until a single phase model is developed.

I concur with haze10. Assume that the fault can develop into a 3Ø 480 volt fault. Do this as a conservative assumption even if the other phases are not present because there is no industry accepted way to calculate the energy otherwise.

Duke's heat flux calculator does the job for single phase arc fault in air but requires arc current input. Take a loot at this:

http://www.arcadvisor.com/pdf/DukeHeatFluxCalculatorGuide.pdf

Here's an example of 277v single phase causing an explosion. (I'm assuming was a 277v fixture.)

Does this mean we should do AF calcs and put AF warning labels on every 277v lighting fixture?

http://www.ktla.com/news/landing/ktla-hospital-evacuated,0,1235173.story

KTLA
Explosion Prompts Evacuation of SoCal Hospital

KTLA News
July 10, 2009

GLENDORA -- Authorities say part of Foothill Presbyterian Hospital in Glendora was evacuated early this morning after a flourescent light fixture suddenly exploded.

The incident occurred around 12:45 a.m. in the emergency room of the facility, which is located on South Grand Avenue.

When firefighters arrived, two hospital employees and a civilian complained of eye irritation, but all declined treatment, according to a Los Angeles County Fire Department dispatch supervisor.

Firefighters evacuated the emergency room while hospital maintenance crews searched for the source of the explosion.

The emergency room was expected to reopen sometime before 3 a.m., the dispatch supervisor said.

The explosion was traced to a lighting ballast, which maintains the electrical current in fluorescent fixtures.