Thermal Limit for Bare Copper Grounding Conductor

[SindhuK]

Hi,

I am looking for some good reference on thermal limits for bare copper wires used as grounding electrode conductors. IEEE 242 buff book and other resources on internet only specified final temperature limits for insulated conductors. I couldn't find much on bare conductors, not even in cable manufacturers datasheets.

SKM software is using 340 deg C for bare overhead aluminum wires

http://www.skm.com/applicationguides4.html

In order to verify the short circuit capability is it safe to consider 250 deg C as max limit? This is specified in the below link.

http://www.cooperindustries.com/con...ductor_Protection_Wire_Cable_Protection_2.pdf

Thanks.

 

[7anoter4]

IEEE 80/2000 Guide for Safety in AC Substation Grounding
11.3 Conductor sizing factors 11.3.1 Symmetrical currents:
Tm is the maximum allowable temperature in°C
Table 1—Material constants
Fusing temperature Tm 1083 °C . Note a:
See 11.3.3 for comments concerning material selection.
11.3.3 Additional conductor sizing factors
The designer should take precautions to ensure that the temperature of any conductor and connection in the grounding installation does not pose a danger to the safe operation of the substation. For instance:
a) Typically, conductors and connections near flammable materials should be subject to more stringent temperature limitations.
b) If the strength of hard drawn copper is required for mechanical reasons, then it may be prudent not to exceed 250°C to prevent annealing of the conductors.
IEEE Std 837-2002 IEEE Standard for Qualifying Permanent Connections Used in Substation Grounding.
Table 5—Conductor temperature : Copper 350 °C.

BS 7430:1998 Code of Practice for Earthing-
Table 10 — Earth fault current densities for 1 s duration for earthing conductors with initial conductor temperature of 30 °C
recommends a maximum permissible temperature of 250oC for bolted joints, 450oC for brazed joints and 700oC for welded joints but 150oC for soft soldered
Note: It should be verified that a material likely to be in the same location as the conductor will not be damaged or present a fire risk at the temperature selected.