In grounding calculation, Maximum allowable fusing temperature (Tm) is indicated (1083 degree C) in IEEE-80-2000 (Table-1-Material constants), but in calculation we have been taking 250 degree C, whats the reason behind this...Please give yours opinion.

where strength of copper conductor is required for mechanical reasons, 250.c shall be selected. normally for calculating of riser conductor that is connected to structure by bolted connection (like as cable lug) 250.c is selected.
where there is welding connections (like as under ground earth grid) you can use 1083.c
melting point of copper is 1083.c so in my opinion, it is better consider lesser value in calculation for more reliability.

It means if Grounding mesh designed for welded type connection, we will use 1083 dC input as for maximum allowable temperature. and if Grounding mesh is designed for Compression type joints connection through Nuts & Bolts, input should be 250 dC.

Again for above ground connection to structures always considered as worst case as 250 dC.

Thanks a lot.....

Is it safe to base calculations on melting point instead of a FOS of at least 2?.