Hello all,

I have seen posts referencing this but not directly.
1) Would it seem correct that if I am using the tables from 70E that I am required to don HRC 2* PPE to test if a 277V ballast in a light fixture is de-energized?
2) Would only HRC 2 be required for 120V ballast?
3) If my AF study is complete and the panelboard feeding these fixtures is determined < 1.2 cal/cm2 then HRC 0 is required to check for a de-energized ballast?

Thank you for any information.

1. AF is a 3 phase hazard and 277V is single phase. Not applicable.
2. Same as for #1
3. Again are you testing on single phase circuit?

Not quite.

AF is a hazard even on single-phase circuits, so PPE is required.
It is just that IEEE-1584 does not contain a methodology for determining the incident energy of a single phase fault.

1) Yes.
2) Wouldn't you use "Panelboards or Other Equipment Rated 240V and Below - Work on energized...fed directly by a branch circuit..." HRC = 1?
3) Yes. Strictly speaking, the calculations are for 3Ø only, but if the single phase fault current is enough to trip the MCCB on instantaneous, then the IE calculation should be conservative.

I am not saying that there are not hazards but if you refering to strictly arc flash hazards, which are only calculated on a 3 phase system, then the single phase arc is not included. That is not to say that a single phase arc could not happen.

A lot of facilities will have basic PPE requirements for the electrician that should suffice for single phase work.

Duke, among others, has a method of calculating incident energy for single phase systems.

If incident energy is not calculated, 70E requires you to use their task tables.

No where do I see an arc flash exemption for single phase.

I want to say that working on a single phase ballast (120 or 277V) would be HRC 0. But I do not see how I can justify that as I am using the tables to dictate my arc flash PPE at this time.

I am wary about going outside of the tables if I do not have my full study done.

Does most work not listed fit into the "work performed on energized...fed from circuit" category?

for 4 phase systems, as per standard if equipment is below 240V and fed by transformer 125kVA and below, then HRC = 0, so if this 277V system is fed by a transformer of 125kVA and below, which is likely, and since it is single phase (likely resulting in smaller arc flash energy than 3 phase), then I would say it is safe to assume HRC=0, but I see no problem in the extra protection in the tables if the client and electricians wish so, as standards only provide minimum protection requirements

3 phase not 4 phase*

What you say might make sense for the 120 volt ballasts, but 277 > 240. Even so, NFPA 70E does not say that equipment below 240V is HRC=0. It says that an arc flash hazard analysis is not required. It is not clear whether HRC=0 can be used or if the task tables should be used, which would require HRC=1.