Back in 2016 I started taking the approach of using "generic" labels for 120/240V single phase panelboards and load centers for small single phase services based upon the data available to me at the time. I printed labels that basically said "less than 8 cal/cm^2", as the daily wear PPE for electricians there was 8 cals. I had many buildings to label back then, but not many like that since. They were almost houses that had been converted to office spaces on a university campus.

Someone asked me about this generic labeling yesterday, so I decided to look into newer information on the subject and found these two papers:

https://electricalsafetyworkshop.org/wp ... 023-06.pdf

https://electricalsafetyworkshop.org/wp ... 24-33r.pdf

Test setups in a lab were built to test 240V single phase and higher. Test results were basically all just a fraction of a calorie/cm^2 with arcs not being able to self sustain with parallel electrodes like you would have in a typical panelboard. One of the studies the conducted tests with the electrodes in-line, end-to-end as well, as opposed to parallel. ie the worst case scenario for trying to sustain an arc. They were able to get sustained arcs and measurable incident energies in the end-to-end, "in-line" configuration. I can't really envision what a "real world" in-line condition in a panelboard or load center would be.



Any thoughts on this? How do you label single phase panels? Today, if I have the occasional 120/240V single phase panel as part of a larger 3 phase distribution system, I just model those one or two or three panels as 3 phase since that is supposed yield a conservative result. Many others probably do the same.

What I am specifically asking about is, this residence converted to an office scenario. Opinion on generic labeling? Less than 1.2 cals? 4 cals? 8 cals? Higher?

Brent,

I've used the 3 phase modelling approach too in the past. However, these days after reading a number of papers on the topic (I have seen / read at least one of those), I use a "<=1.2cal/cm2" generic label unless we're talking larger electrical system sizes (which I know is arbitrary).

Mike

Thanks for the reply, Mike.

I suspect most folks are modeling as 3 phase or if their software license has the single phase calculation capability, using that. One of those papers says something like the software grossly over estimates IE though. Kind of like it does for pad mounted transformers being 60 or 80 cals or even higher IE when testing couldn't get higher than 4 cals due to large bus gaps and enclosures. That is why the NESC went to 4 calories for 480V and under pad mounts. At least the last time I checked it was still that way but it's been a few editions ago.

I don't have the single phase module with my SKM license so I don't know what formulas they are using nor have I compared those results with the 3 phase output.

Brent

Brent,

Likewise...no single phase module. Also in the NESC, look at the 208V equipment AF PPE recommendations. I also base my PPE selections based on the footnotes in NESCs PPE table. I'll also often use 10 cycle clearing for 208V systems...

Mike