Arc Flash Concerns

[BMacky]

I've been seeing a lot of information on arc flash over the past few years, reading a few articles here and there and getting somewhat aware of the hazards, though it is never really written that there are certain thresholds where this is more likely to be an event. IS there a standard practice for say, what type of gear, voltage/amperages to be more concerned about this than say a typical residential 200A service?

I suppose arc flash can happen under certain circumstances at lower amperages/voltages, but is it written anywhere that working on equipment at or above so many volts/amps that protective clothing/gear is a must or recommended?

I have a job coming up where the equipment is an 800A main and we need to add a breaker to the panel. I figure this is probably a time to show some concern. The voltage is 120/240 with a stinger leg.

Better safe than err on this, so any of you readers that have some guidance please chime in.

Thanks.

 

[charlie b]

It may seem counter-intuitive, but lower voltages can, under the right overall circumstances, create a far more severe arc flash hazard than higher voltages. The degree of arc flash hazard is strongly related to the amount of time it takes for some upstream overcurrent device to open the circuit and terminate the event. The lower the fault current, the longer it will take for the overcurrent device to actuate. So don?t presume that your work is safer on an 800 amp, 120/240 panel, then it would be on a 2000 amp, 480/277 panel.

You are right to say this is a time to show some concern. If the panel does not already have a label that declares the arc flash hazard level or the PPE requirements, then I recommend that you not perform this job live, until those two things are determined. Naturally, it would be better still to convince your boss and the owner of the facility to figure out how to arrange for the equipment to be turned off, before you proceed with the installation of the new breaker.

 

[BMacky]

Thanks, Charlie. The panel is easily secured and the tenants don't work weekends so I planned to get this done on a Sunday morning and power down.

I thought that I'd at least get up to speed on arc flash requirements after looking at some protective gear on display with the budget for this job in mind.

Thanks for the quick reply!

Bob

Foster City, CA