Arc Flash Analysis

[rnkish]

When performing an arc flash analysis you are required to wear the proper PPE. What is the proper PPE if an analysis in not yet done?

 

[zog]

Use the 70E Tables

 

[S'mise]

You wear your ppe and treat it as the worst case until you confirm otherwise.
like Zog said, see nfpa70E

 

[rnkish]

Proper PPE

Proper PPE

Table 130.7(C)(9)(a) is the table i assume you are refering to.

If I remove a cover and the dead front from a 200a 277/480v Panelboad (available fault current supplied by the local utility is 42 KA) to retrieve catalogue numbers and trip settings only off of the breaker labels the way I read the table is a PPE of 1 is required.

I am seeing this in the second section of the table for Panelboards or switchboards Rated >240V and up to 600V.

Why do you think a listing for "Removal of bolted covers (to expose bare, energized parts)" is not listed here as it is in the previous part of the table Panelboards Rated 240V and Below??

Am I reading this correct??

 

[charlie b]

When performing an arc flash analysis you are required to wear the proper PPE.

I don't. I have done but a few analyses, but I haven't worn any special PPE during any one of them. :wink: :grin:

 

[billsnuff]

see other 600V class (277 throught 600) equipment..........I think your answer is there, see note 2*. JMSO

 

[zog]

Table 130.7(C)(9)(a) is the table i assume you are refering to.

If I remove a cover and the dead front from a 200a 277/480v Panelboad (available fault current supplied by the local utility is 42 KA) to retrieve catalogue numbers and trip settings only off of the breaker labels the way I read the table is a PPE of 1 is required.

I am seeing this in the second section of the table for Panelboards or switchboards Rated >240V and up to 600V.

Why do you think a listing for "Removal of bolted covers (to expose bare, energized parts)" is not listed here as it is in the previous part of the table Panelboards Rated 240V and Below??

Am I reading this correct??

Yep, the 2009 70E address this more specifically, they added a "perform IR inspection and other non-contact inspections " task in that section - HRC 1 also.

 

[zog]

see other 600V class (277 throught 600) equipment..........I think your answer is there, see note 2*. JMSO

Correct, removing hinged or bolted covers to expose bare energized parts is in that section, HRC 1 and 2* (Hinged/Bolted)

 

[billsnuff]

after cover removal

after cover removal

you would then need to comply with the approach boundaries found in 130.2(C)..............correct?

 

[zog]

That is correct

 

[ron]

Let's pretend you used a Category 1 PPE from the table to make your survey, then after calculation, you determine that the incoming service OCPD's had no instantaneous protection, and the short time was dialed to the max, and you find incident energy >40 cal/cm^2 for several downstream pieces of equip.
When you would do your next survey for a study at another building, would you just follow the table and wear PPE 1?
Another angle is that I've done many calculations, even at 120/208V panelboards, that have very low fault current and took the equivalent of what might be infinity to have the upstream breaker clear, and determined incident energy at 200cal/cm^2. Yikes!

 

[zog]

Let's pretend you used a Category 1 PPE from the table to make your survey, then after calculation, you determine that the incoming service OCPD's had no instantaneous protection, and the short time was dialed to the max, and you find incident energy >40 cal/cm^2 for several downstream pieces of equip.

Then you are not using the tables correctly, they have limitations (Notes section) on fault current and clearing time.

 

[coulter]

... Another angle is that I've done many calculations, even at 120/208V panelboards, that have very low fault current and took the equivalent of what might be infinity to have the upstream breaker clear, and determined incident energy at 200cal/cm^2. Yikes!

Ron -
Take a look at IEEE 1584, Appendix B (I think) for the "2 second rule". My translation is if you are still functional after 2 seconds, you will move away - your body won't let you stay there, no matter what your mind says. I don't know what NFPA 70E says.

Another issue about the calcs: Look at the limitations on the model. As I recall, IEEE 1584 doesn't apply to less than 250V (or so) - apparently IEEE doesn't think 208V will sustain an arc-flash.

As zog said - check the limitations in the notes.

carl

 

[zog]

Let's pretend you used a Category 1 PPE from the table to make your survey, then after calculation, you determine that the incoming service OCPD's had no instantaneous protection, and the short time was dialed to the max, and you find incident energy >40 cal/cm^2 for several downstream pieces of equip.

There is an easy solution to that, upgrade the breaker to an AC PRO with QUICK TRIP, arc flash reduction switch. We do dozens of these a month, great mitigation solution. Mitigation solution recommendations should be part of every study.

 

[ron]

The table notes relate to available fault current and clearing time. Until you do the survey, how do you know if you are compliant with the notes.
The breakers I'm describing have new solid state trip units already, although the instantaneous is off in order to have selectivity.
It is always a balance between reliability and arc flash reduction, and many critical facilities prefer reliability.

 

[zog]

The table notes relate to available fault current and clearing time. Until you do the survey, how do you know if you are compliant with the notes.

You dont, but is the breaker dosent have INST you should know the tables can not be applied.

The breakers I'm describing have new solid state trip units already, although the instantaneous is off in order to have selectivity.

I thought your statement was generic, didnt think you were describing anything in paticular.

It is always a balance between reliability and arc flash reduction, and many critical facilities prefer reliability.

Exactly, and that is the exact reason that arc flash reduction switches are made by most OEM's as a solution to both. IMO AC PRO just has the best design and product.

 

[jim dungar]

It is always a balance between reliability and arc flash reduction, and many critical facilities prefer reliability.

I am always amazed how routinely some critical facilities allow energized work. I wonder how many do a risk analysis of an unexpected outage occurring. Dialing down the selectivity to reduce the arc flash energy during live work actually increases the chance of an unexpected outage

 

[ron]

Carl,
From a liability standpoint, I can't stop the calculation at 2 seconds, because the first worker that gets their PPE stuck on a cubicle door during an incident and can't get away, there will be lots of questions regarding why the PPE wasn't selected based on 3 seconds or 4 or 5 or as long as it actually takes the OCPD to clear.

 

[GMIEE]

So do you actually put a label on equipment that shows something like 1000 ft. boundary?