Premissible short circuit temperature and the prospective fault level for
cables and their insulation

Based on the final (permissible) short circuit temperature of a duration of 1 sec, the values for calculating the prospective fault are listed below.
Insulation

Permissible Rated
Operating
Temperature
°C

Permissible Short
Circuit
Temperature
°C

Conductor temperature at the beginning of the short circuit in °C

180
165
150

135

120

105
90
80
70
60
50
40
30

thr for 1 sec in A / mm2
Silicone
180
350
132
139
146
153
160
166
173
178
182
187
191
196
201
PVC
75
150
                
109
117
124
131
138
EPR
Unitnned Conductor
Tinned Conductor
 
90
90
 
250
200
            
 
143
122
 
148
128
 
154
135
 
159
141
 
165
147
 
170
153
 
176
159
EVA
125
200
        
126
135
143
148
154
159
165
170
176

Tinned Conductor

  
200
49
65
79
91
102
112
122
128
136
141
147
153
159

Soldered Joint

  
160
    
36
58
74
87
100
107
115
122
129
136
143

 

Formula for calculating the Fault level 1thr of a cable
/ thr =    thr x conductor size in mm2
Example   A4 x 35mm2 PVC/PVC fully loaded and therefore having a continuous conductor operating temperature of 75°C
     
/ thr = 109 x 35
  = 3.81 kA for 1 second
     
For fault durations up to 5 sec or below 1 sec the following equation is applicable (example is for 0.2 sec fault)
     
   

                1 sec

/ thz = / (1s) x ¡Ô0.2sec