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Enclosure Size Equations and Calculator for Arcing Current per IEEE 15842018
Electrical and Electronics Design and Engineering
Enclosure Size Equations and Calculator for Arcing Current per IEEE 15842018
Once the enclosure type has been classified, the equivalent height and width need to be determined by comparing their values against specific ranges for each of the three electrode configuration.
Related:
Arc Flash Hazard Calculations Procedure and Considerations For Medium Voltage System
For certain ranges, the equivalent height and width are determined using the following equations and calculator:
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Equation 1
See Table 1 for Alternate Eq. 

Equation 2
See Table 1 for Alternate Eq. 

Equation 3


Equation 4
Correction Factor for "Typical Enclosure" 

Equation 5
Correction Factor for "Shallow Enclosure" 
Where:
Height_{1} = Equivalent enclosure height
Width_{1} = Equivalent enclosure width
Width = Actual enclosure width (mm)
Height = Actual enclosure height (mm)
Voc = Opencircuit voltage (system voltage) (kV)
A = Constant, equal to 4 for VCB and 10 for VCBB and HCB
B = Constant, equal to 20 for VCB, 24 for VCBB, and 22 for HCB
EES = Equivalent enclosure size used to find the correction factor, typical enclosures the minimum value of EES is 20.
CF = Enclosure size correction factor
b1, b2 and b3= Coefficients from Table 2
Determination of enclosure type—Typical or shallow
The enclosure is “Shallow” when the following conditions are met:
a) The system voltage is less than 600 V ac.
b) Both the height and width are less than 508 mm (20 in).
c) The enclosure depth is less than or equal to 203.2 mm (8 in).
If any of these conditions are not met, the enclosure is considered “Typical.”
The table below provides the guidelines to determine the equivalent enclosure height and width (Height1 and Width1) for different ranges of enclosure dimensions and electrode configurations.
Table1
E.C.

Range

< 508
(mm) 
≥ 508 and ≤ 660.4 (mm)

> 660.4 and ≤ 1244.6 (mm)

> 1244.6 (mm)

VCB

Width_{1}

= 20 (if Typical)
= 0.03937 × Width (if Shallow^{a}) 
= 0.03937 × Width

obtained from Equation (1)
and actual Width 
obtained from Equation (1)
with Width = 1244.6 mm 
Height_{1}

= 20 (if Typical) or
= 0.03937 × Height (if Shallow^{a}) 
= 0.03937 × Height

= 0.03937 × Height

= 49


VCBB

Width_{1}

= 20 (if Typical) or
= 0.03937 × Width (if Shallow^{a}) 
= 0.03937 × Width

obtained from Equation (1)
and actual Width 
obtained from Equation (1)
with Width = 1244.6 mm 
Height_{1}

= 20 (if Typical) or
= 0.03937 × Height (if Shallow^{a}) 
= 0.03937 × Height

obtained from Equation (2)
and actual Height 
obtained from Equation (2)
with Height = 1244.6 mm 

HCB

Width_{1}

= 20 (if Typical) or
= 0.03937 × Width (if Shallow a) 
= 0.03937 × Width

Equation (1)
and actual Width 
obtained from >Equation (1)
with Width = 1244.6 mm 
Height_{1}

= 20 (if Typical) or
= 0.03937 × Height (if Shallow^{a}) 
= 0.03937 × Height

obtained from Equation (2)
and actual Height 
obtained from Equation (2) with Height = 1244.6 mm 
Coefficients for Equations 4 and 5
Table 2
Box Type 
E.C.

b1

b2

b3

Typical Enclosure 
VCB

0.000302

0.03441

0.4325

VCBB

0.0002976

0.032

0.479


HCB

0.0001923

0.01935

0.6899


Shallow Enclosure 
VCB

0.002222

0.02556

0.6222

VCBB

0.002778

0.1194

0.2778


HCB

0.0005556

0.03722

0.4778

VCB: Vertical conductors/electrodes inside a metal box/enclosure
VCBB: Vertical conductors/electrodes terminated in an insulating barrier inside a metal box/enclosure
HCB: Horizontal conductors/electrodes inside a metal box/enclosure
VOA: Vertical conductors/electrodes in open air
HOA: Horizontal conductors/electrodes in open air
Reference:
IEEE 15842018
Verify results and send feedback if a discrepancy is found.