Single Phase, 230V

I am working on an arc flash study that includes several 240V single phase pump stations for a municipality. They are 2hp, 230v, single phase grinder pump stations, one for each homeowner's lot and the control panel is in the homeowner's basement.

Not sure if these fall under the <240v category. Is this a situation where the tables are better used?

Most testing shows self extinguishing arcs at other than high arcing currents at 240 volt three phase. In single phase systems where you get voltage zero, it is highly unlikely that an arc can sustain itself. I do not believe there is any valid testing, therefore, anyway to calculate low voltage single phase arc flash energies.

Chet Davis from Easy Power has delivered an interesting paper on 208V arc flash energies. He uses a max arc time or cut-off of .5 seconds and mathematically shows this approach gives a safety factor of five. If you use that same logic, the self-extinguishing nature of single phase (at 230 volts) circuits would show negligible incident energy.

To take it one step further, I do not see how you ever show energies greater then 1.2 cal for an overcurrent device that small. It was never the intent to take studies down to circuits that small, no matter how hard some engineers try to convince their clients otherwise.

Dwellings

A couple of thoughts... it appears you are dealing with dwellings. Research the NFPA 70E to see the requirements for dwellings (exempt). Most electric services to single family dwellings (and many commercial facilities) are <125kVA <= 240V so there is no arc flash hazard. Chet's article has shed a lot of light on the topic!

Have you done some lab tests at 240 V center tap? Or aware of somebody else who did some? That's what normally goes into dwellings. The absence of the 2 other phases should lessen the amount of energy available to be released during an arc flash event, when the arc current is the same.

230 is a nominal utilization voltage for 240 services. I would not call this < 240, since measured voltage will likely be higher. In my opinion the <240 rule is for 208 services.

<240 125kva

I agree that this is the most controversial issue pertaining to arc flash studies. This is also a major cause for the arc flash study results' (for these voltage levels) loss of credibility. While that "pop" and molten BB's dancing on the floor gets our attention, I don't believe that is the crux of the arc flash hazard analysis. While this may technically be an arc flash, so is turning off a 120v light switch. So, where do we say that there is no arc flash hazard? Technically the answer should be never. In reality, we know that the "pop" is not the hazard that we need to address as compared to the high energy 3 phase systems. The studies that I have seen where a <240v arc did sustain, it didn't have the explosive energy associated with the classic arc flash.

Hopefully, we will work toward a realistic solution that protects employees without being a cumbersome process. That is why I like Chet's interim solution... it blends safety with common sense.

My only question is "Why were you working on the panelboard with it energized?"... hopefully it was for diagnostics. I too have ruined more screwdrivers than I like to admit!