Ok folks, I'm a manager for a large manufacturing corporation. We're trying our best to comply to NFPA 70E. We're pretty far along in our journey. We have our panels and subpanels analyzed and labeled with the official cal/cm ratings. Our issue is how to select the proper PPE downstream of our labeled panels. We launched with the requirement that anything downstream must be treated as having the same cal rating as the upstream device. I just observed a 120 single phase outlet that is fed by a panel marked with a 13 cal rating. Our issued PPE for our maintenance technicians goes up to 12 cal. Of course, there's a circuit breaker that significantly reduces the arc flash potential. It's not feasible to label everything downstream from our panel. Is there a better way to select proper ppe for equipment downstream? As you can tell, I"m not an Electrical Engineer. I'm just a concerned manager trying to do the right thing.

IEEE 1584 only deals with 3 phase systems. You might reference this article: https://www.electricityforum.com/iep/ar ... lculations which talks about single phase arc calculations.

I would say it isn't the intent of the NFPA 70E to require 13 cal/cm2 arc rated clothing to work on a receptacle or any other downstream load for that matter. But this does beg the question, "can you de-energize and then work on the receptacle?" While it doesn't eliminate the arc flash risk at the point where you are turning the power off (circuit breaker feeding the receptacle in your example), it does eliminate it at the receptacle.

Mike

Thanks for the reply. The work needing to be performed requires the power to be on for troubleshooting.

What are you doing with the outlet? Are you simply plugging and unplugging cord connected equipment? Or are you opening it up and exposing live and energized parts of the outlet?

This is a really great question. For many years, everybody I know in the electrical trade has been familiar with the "breaker finder." In older plants with unmarked panels the use of this device was very common and often used as an additional precaution to make certain that the correct breaker was turned off. How many people on this forum have experienced an arc flash or other incident in the past with the use of one of these devices?

45 years using "breaker finders". Not 1 flash.

I would not be concerned about arc flash and a 120 VAC electrical outlet. Tests have shown that equipment rated 240 or less can not sustain an arc flash event. The arc flash will self extinguish no longer than 2 cycles. See National Electrical Safety Code NESC-C2 Table 410-1.

Bob Fuhr is completely correct. The 13 cal is for the 3P panel, NOT the recepticle.

If a 120V control wire is in a 480V MCC the small arc from the 120V wire could cause the 3P to arc and be a hazard but outlets have never ignited clothing in my experience. This is a shock hazard ONLY. I would wear gloves doing voltage testing but the risk is VERY low and the consequence is likely to be only shock.

Hugh Hoagland
ArcWear/e-Hazard.

Hi Mdowil

I'm a Canadian Red Seal Journeyman electrician certified to work nationally starting in 1975.

That is a four year apprenticeship where you complete 9,000 hours of one to one OJT and mentoring with an experienced journeyman.

In addition you have 8-10 weeks of trade school at the end of every year that totals over 1,200 hours of class room training.

Once you have successfully completed your schooling and amassed your hours you write the Red Seal national exam.

This is a complex exam with a significant failure rate.

In the "old" days we worked on these circuits bare hand all the time.

High line technicians work on 500,000 volts live using safe work procedures and most importantly, safe work practices.

These same work procedures and practices can be employed on 120V branch circuits but it takes similar dedicated OJT and experience. The difference is that we have PPE for 120V.

For technical reasons to do with circuit impedance, your danger on a 120V branch circuit is not arc flash.

It is electrocution and it is a very real danger that your workers need to have constantly in mind around all circuits,

If your workers are using rubber gloves with leathers and your 12 cal clothing they are protected from both dangers.

I have seen both intentional and unintentional 120V branch circuit flashes.

I have never seen one that would cause even a second degree burn but they do wreck your Kleins.

The surprise of the unintentional ones scare the crap out of you which can lead you to a physical reaction danger.

Bottom line is train your workers to fear all three dangers but for a company procedure using the PPE and following Safe Work Practices will protect your workers when troubleshooting live 120V branch circuits.

Sincerely
Dave Smith
President
Canada Training Group

I am not sure the original question is addressed here, only the original scenario. What if you look at this from a 3-Phase circuit. You have a 480V 3-Phase panel with 17 cal/cm2 potential that feeds a small 480V 3-Phase 1 HP motor that is 250' from the panel. What would the required PPE be to open the disconnect and check the voltage on the disconnect at the motor?

In response to your question about a remote 480V 3ph motor off of a 3ph 17 calorie bus, you need to do the arc flash analysis for determination of the incident energy (IE) level at the motor. It could be higher due to the increased impedance of the 250' run and slow to trip the breaker so the IE builds up.