Arc Flash Analysis PPE Tables

[Grouch1980]

Hey guys,
I'm learning how ( / trying ) to do arc flash analysis. I went through the equations and sample problems in NFPA 70E (2024 version) and also IEEE 1584 (2018 version).

NFPA 70E gives you incident energy values in calories / cm2.

IEEE 1584 gives you incident energy values in J / cm2.

I know the values are interchangeable.

Once you get the final results, whether NFPA 70E or IEEE 1584, where do go in each of these standards to determine the level of PPE required? Which tables do you use?

Thanks!

 

[David Castor]

If you are calculating incident energy using IEEE 1584, the PPE requirement is basically the calculated cal/cm2. NFPA 70E calls this the Incident Analysis Method. There are tables in NFPA 70E that can be used instead of doing the calculations, but with a lot of restrictions - this is referred to as the Categories Method. You use one or the other.

1.2 cal/cm2 = 5 Joules. IIRC.

 

[Grouch1980]

Are you talking about Table 130.7(C)(15)(C)... is this the categories method?

So once you calculate the incident energy, not using the categories method but actually running the calculations, you don't choose a level of PPE that's required based on the calculated cal/cm2 or j/cm2? If not, then what's the next step? who chooses the PPE equipment?

 

[TheEngineerEEE]

When performing Incident Energy calculations, it may not always be necessary to select a specific PPE level; this decision typically depends on the client's requirements. The incident energy (cal/cm2) is usually reported on the Impedance One-Line Diagram and on the Arc Flash Labels. This information can be used to determine the appropriate PPE for the equipment. For guidance on selecting the right Arc-Rated Clothing and other PPE when using the Incident Energy Analysis Method, refer to NFPA 70E Table 130.5(G).

 

[Grouch1980]

This information can be used to determine the appropriate PPE for the equipment.

So the arc flash label only has to indicate the incident energy... and then whoever decides to perform work on the equipment, that company determines the PPE that's required, based on NFPA 70E Table 130.5(G)?

For guidance on selecting the right Arc-Rated Clothing and other PPE when using the Incident Energy Analysis Method, refer to NFPA 70E Table 130.5(G).

is there a similar table in IEEE 1584?

 

[jim dungar]

So the arc flash label only has to indicate the incident energy... and then whoever decides to perform work on the equipment, that company determines the PPE that's required, based on NFPA 70E Table 130.5(G)?

is there a similar table in IEEE 1584?

IEEE 1584 is about performing the mathematics required to calculate arc flash incident energy.

NFPA 70E is about electrical safety such as determining what procedures must be followed.

The answers to your questions should be found in the company's Electric Safe Work Practices program which is usually looked at by OSHA during an investigation.

 

[Grouch1980]

NFPA 70E is about electrical safety such as determining what procedures must be followed.

The answers to your questions should be found in the company's Electric Safe Work Practices program which is usually looked at by OSHA during an investigation.

the NFPA though has its own set of equations as well, in Annex D. the results you get, from what I read, are more conservative than IEEE. However the equations are only valid within a certain short circuit range... a smaller range than IEEE.

 

[Grouch1980]

IEEE 1584 is about performing the mathematics required to calculate arc flash incident energy.

NFPA 70E is about electrical safety such as determining what procedures must be followed.

I see what you're saying... there are no PPE requirement tables in IEEE 1584... it only goes through the math. So any PPE tables are in NFPA... do I have that right?

 

[David Castor]

Yes, but again, if you are calculating the incident energy, generally the incident energy in cal/cm2 is put on the label, not a PPE category. Table 130.5(G) (in my old version of 70E at least) is for "Selection of Arc-Rated Clothing and Other PPE When the Incident Energy Analysis Method Is Used". But it does not refer to the PPE categories 1 through 4 that are used when calculations are not done.

So if the label has an incident energy of 5.9 cal/cm2, the basic requirement is that the PPE selected must have a minimum rating of 5.9 cal.

 

[Grouch1980]

Yes, but again, if you are calculating the incident energy, generally the incident energy in cal/cm2 is put on the label, not a PPE category. Table 130.5(G) (in my old version of 70E at least) is for "Selection of Arc-Rated Clothing and Other PPE When the Incident Energy Analysis Method Is Used". But it does not refer to the PPE categories 1 through 4 that are used when calculations are not done.

So if the label has an incident energy of 5.9 cal/cm2, the basic requirement is that the PPE selected must have a minimum rating of 5.9 cal.

I see, understood. I have the 2024 version of NFPA 70E... table 130.5(G) still has the same title.

 

[jim dungar]

the NFPA though has its own set of equations as well, in Annex D. the results you get, from what I read, are more conservative than IEEE. However the equations are only valid within a certain short circuit range... a smaller range than IEEE.

NFPA 70E does not care how you arrived at the incident energy values, as long as it is industry recognized. Its Annex are usually optional or simply informative.

 

[Grouch1980]

NFPA 70E does not care how you arrived at the incident energy values, as long as it is industry recognized. Its Annex are usually optional or simply informative.

If optional, should one follow the calculation methods in Annex D of NFPA 70E, in addition to IEEE 1584? I would do them anyway, just trying to gather what you guys do.

 

[jim dungar]

We only used IEEE 1584 unless a customer specified otherwise.

 

[Grouch1980]

We only used IEEE 1584 unless a customer specified otherwise.

ok got it.

Thanks everyone for the help.

 

[mayanees]

The Categories Method uses table 130.7(C)(15)(c)
The Incident Energy Analysis method uses Table 130.5(G)

I think the Categories Method only applies to about 1/3 of the real-world situations since there are fault current and fault clearing qualifiers that minimize the applications. It's always better (IMO) to do the incident energy calculations. However, IEEE 1584 only applies from 208V- 600V for currents ranging from 500-106kA and 601V-15kV for currents from 200A to 65kA, at which point other methods in Annex D are used for the incident energy calculations.

 

[Grouch1980]

since there are fault current and fault clearing qualifiers that minimize the applications.

What do you mean by qualifiers?

at which point other methods in Annex D are used for the incident energy calculations.

Which annex D? you mean the one in NFPA 70E?

 

[mayanees]

What do you mean by qualifiers?

They refer to them as Parameters in Table 130.7(C)(15)(a) like maximum current of 25kA, 42kA, 65kA. That's calculated by using the infinite primary method to calculate the maximum available fault current - which is the upstream transformer's fla/Z or full-load-amperage divided by the transformer's impedance.
Another parameter or qualifier is the maximum fault clearing time in cycles or seconds.
And the last one is the working distance which is always 18 inches for 600V and below, whereas with switchgear that can be 24" when using the Incident Energy (IE) calculation method.
I think this is a big reason why the IE method and arc flash labels is preferred because not only are there the "parameters" that must be met, but you also have to determine the upstream source; i.e. transformer size, to calculate the available fault current. Not to mention the case where you're opening up the secondary of a transformer where there is no upstream device that you can use for the fault clearing time.

Which annex D? you mean the one in NFPA 70E?

Yes, Annex D is in NFPA 70E - Incident Energy and Arc Flash Boundary Calculation Methods.