Cut Sheet

SECTION BTECHNICAL INFORMATION
CONSTANT K FOR ABOVE FORMULA
MAX COPPER COPPERWELD DSA COPPERWELD DSA
TEMP S.D. 40% 30%
1083 C 7.01 10.46 12.04
450 C 9.18 13.74 15.87
350 C 10.10 15.13 17.46
250 C 11.65 17.47 20.17
GROUNDING SYSTEM – CONDUCTORS AND CONNECTORS
This formula can be simplified to the following:
Where: A = Conductor size in circular mils
K=Constant from the following table
A= K • I S I = RMS fault current in amperes
S=Fault time in seconds
Based on the standard ambient temperature of 40°C.
The grounding conductor size is based on the
maximum magnitude and duration of available fault
current, and on the type of connections being used in
the grounding system.
IEEE Std. 80-2000, Guide for Safety in Substation
Grounding, the accepted industry standard, uses a
fusing formula as the basis for selecting minimum
conductor size to avoid fusing (melting) under fault
conditions.
The temperatures listed above for each material are specified in IEEE Std. 80-2000 to be used for different types of
connecting means;
Pressure type connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250° to 350°C*
Brazed connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450°C
Exothermic welded connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083°C
*except those which have been tested to and passed the requirements of IEEE Std. 837-1989.
EXAMPLE – 25,000 Ampere, 2 second fault:
CONNECTION TYPE CONDUCTOR SIZE
CADWELD . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246 kcmil – use 250 kcmil
Brazed . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322 kcmil – use 350 kcmil
Pressure Type (at 350 C) . . . . . . . . . . . . . . . . . .357 kcmil – use 350 kcmil
Pressure Type (at 250 C) . . . . . . . . . . . . . . . . . .408 kcmil – use 400 kcmil
√
+31% +41% +66%
Cable
Only
CADWELD
Connections
Brazed
Connections
Pressure Type
Connections
350°
Pressure Type
Connections
250°
B-1
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