Maximum allowable temperature in ecuation 41 of IEEE 80-2000

[radug]

Hello,

When calculating the thermal rating for grounding conductors, Tm (maximum allowable temperature) must be entered in ecuation 41 of IEEE 80-2000.
The standard gives fusing temperatures of different materials (for example 1084 degrees Celsius for soft-drawn copper).
I asked some manufacturer which was the maximum allowable temperature for cadweld type welding and he told me it was above the fusing temperature for copper, so, using copper fusing temperature was ok.
My concern is, do you use some kind of conservative approach when selecting this temperature?
I have been using 250 degrees Celsius for mechanical type connections, as recommended in the standard, but I have doubts about welded connections.

 

[cuky2000]

Exothermic welding (Cadweld) is rated similar to the fusing temperature of copper conductor. The following fusing temperatures are generally used:
Exothermic Weld........~1084 oC
Pressure connectors... 250oC to 350 oC
Brazed connectors .....450oC.

For installation below grade such as ground grid, not directly expose combustion materials, it is acceptable to design to the fusing rating of the weak link component (conductor, connector, etc.)

For installation exposed in air subject to tension, other criteria may be apply with lower temperature to avoid mechanical degradation such as annealing,other metallurgy damages or fire hazard.

Beware that the fusing current for ground grid should be no more than half of the fraction of the short circuit current injected into the ground.

For connector test data see if the enclosed link could help.

http://www.erico.com/public/library/fep/SEIREPORT.pdf

 

[radug]

Thank you,

I did know about that report.

My doubts arised because in IEC and CENELEC standards final temperatures of 300 degrees C are used, with no explanation about welding or mechanical connections.