Calculations > Arc flash

The result of the calculation is the arc incident energy and the category/class of PPE (that limits the potential burn wounds to maximum the second degree burn). PPE classification is different for IEEE 1584 and ISSA. IEEE 1584 follows the classification of the NFPA (National Fire Protection Association). According to NFPA there exist the following PPE categories (see Table 130.7(C)(15)(c) of NFPA 70 E (2018)):

PPE category	Incident energy (E) [cal/cm2]
0	E ≤ 1.2
1	1.2 < E ≤ 4
2	4 < E ≤ 8
3	8 < E ≤ 25
4	25 < E ≤ 40

The PPE category 0 is eliminated in the 2015 edition of the NFPA 70E, in Vision this category is still in use to indicate that the incident energy ≤ 1.2 cal/cm2. The ISSA specifies two PBM classes:

PPE class

Arc energy* (W)

[kJ]

W ≤ 168

168 < W ≤ 320

* arc energy is specified for the installation with Kt = 1 and the working distance of 30 cm

The results are displayed slightly differently for IEEE 1584 and ISSA.

Basic results of IEEE 1584 are:

	Earc	the total incident energy in cal/cm2 at working distance
	PPE category	Personal Protection Equipment specified by the NFPA (‘X’ in case if the incident energy is higher than 40 cal/cm2)
	FPB	arc Flash-Protection Boundary in mm (the minimum distance at which potential burn wounds are limited to maximum the second degree burn, without PPE)

Extended IEEE 1584 results are (right mouse click on an object with the arc flash results):

	Ibf	bolted fault current in kA
	Iarc	arc current in kA
	Earc	the total incident energy in cal/cm2 at working distance
	PPE category	Personal Protection Equipment specified by the NFPA (‘X’ in case if the incident energy is higher than 40 cal/cm2)
	SWD (or Dbn)	Safe Working Distance in mm, IEEE 1584-2002 only (SWD is the minimum distance at which potential burn wounds are limited to maximum the second degree burn, with the specified PPE category (n))
	FPB (or Db0)	arc Flash-Protection Boundary in mm (the minimum distance at which potential burn wounds are limited to maximum the second degree burn, without PPE)
	Rpp	equivalent fault resistance (can be used for further analysis with Fault analysis \| Fault \| symmetric or Protection \| Single fault \| symmetric)

Basic results of ISSA are:

	Warc	the total arc energy in kJ
	PPE class	Personal Protection Equipment specified by the ISSA (‘X’ in case if the arc energy is higher than energy for PPE Class 2)
	Dbn	safe working distance with PPE class n in mm

Extended ISSA results are (right mouse click on an object with the arc flash results):

	Ibf	bolted fault current in kA
	Iarc (or IkLB)	arc current in kA
	Wprot1	maximum protection energy using the specified work conditions with PPE class 1
	Wprot2	maximum protection energy using the specified work conditions with PPE class 2
	Warc	the total arc energy in kJ
	PPE	PPE class (‘X’ in case if the arc energy is higher than energy for PPE Class 2)
	Rpp	equivalent fault resistance (can be used for further analysis with Fault analysis \| Fault \| symmetric or Protection \| Single fault \| symmetric)
	Dbn	Safe Working Distance in mm (SWD is the minimum distance at which potential burn wounds are limited to maximum the second degree burn, with the specified PPE category (n))

Detailed calculation results with details about switching sequences can be get via button Details (right mouse click on an object with the arc flash results and after that click on Details button).

Results of protection calculation

In case arc flash calculation is performed only at one point (for instance, at one node or one side of a branch), the results of corresponding protection calculation can also be shown. This can be done by clicking on the ribbon Extra | Result | Protection – Single fault (by Result the small arrow at the bottom of the icon has to be clicked). Results of the protection calculation for three-phase symmetric fault with Zpp equal to the arc resistance will be given and the details of protection operation can be checked. After that, it is possible to switch back to the arc flash results (this can be done in a similar manner as it was done for protection results).