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AF PPE for ballast replacement?
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Author:  MIEngineer [ Wed Nov 17, 2010 1:50 pm ]
Post subject:  AF PPE for ballast replacement?
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.
Author:  wbd [ Thu Nov 18, 2010 5:26 am ]
Post subject: 
MIEngineer wrote:
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?
Author:  JBD [ Thu Nov 18, 2010 6:19 am ]
Post subject: 
wbd wrote:
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.
Author:  jghrist [ Thu Nov 18, 2010 8:36 am ]
Post subject: 
MIEngineer wrote:
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) 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.
Author:  wbd [ Thu Nov 18, 2010 9:04 am ]
Post subject: 
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.
Author:  JBD [ Thu Nov 18, 2010 10:51 am ]
Post subject: 
wbd wrote:
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.

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.
Author:  MIEngineer [ Thu Nov 18, 2010 1:08 pm ]
Post subject: 
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?
Author:  mahan4 [ Thu Nov 18, 2010 4:22 pm ]
Post subject: 
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
Author:  mahan4 [ Thu Nov 18, 2010 4:24 pm ]
Post subject: 
3 phase not 4 phase*
Author:  jghrist [ Fri Nov 19, 2010 6:47 am ]
Post subject: 
mahan4 wrote:
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


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.
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