Copper Deformation Due to Heat

[MxGxK]

I apologize for asking you to do my work for me, but I am clueless to thermodynamics. I have done a number of searches and reading, but my particular question doesn't appear in text books. Here goes:

Situation:
Compression 2-hole cable lug is bolted to 1/4"x2"x2' bus bar. Lug gets hot enough to melt (~2000degF). Cable insulation melts 6"-8" from lug. Copper busbar unaffected. No discoloration, No deformation.

Question:
How would you expect the copper busbar to behave? Is it such a great conductor of heat that it acts as a heat sink and it suffers no damage? Or, is it such a great conductor of heat that it all rises to 2000degF and discolors and deforms?

 

[MintJulep]

I think it would depend on why things got hot.

Was it high current? The bus bar can probably conduct much more current than the wire/terminal combo. Wire gets hot, bus bar stays cool.

Was it a bad terminal crimp? High resistance locally, high I²R and associated heat. Terminal gets hot, bus bar conducts heat faster than insulated wire.

Was it a loose connection between lug and bus bar?

 

[MxGxK]

The cable was carrying normal load current. The busbar was more than capable of handling the current.

A bad crimp is certainly a possibility.

Would 2000degF localized heating be dissipated by the busbar while causing insulation melting on the cable? I certainly think so but would the busbar exhibit any evidence of heating?

 

[carnage1]

Would 2000degF localized heating be dissipated by the busbar while causing insulation melting on the cable?
yes
maybe not

If the lug melted fast enough, which your description makes it sound like it melted quite quickly, then there would be a very high temperature on the end of the wire and on the mounting spot on the bus bar. The bus bar has a huge thermal capacity and the wire does not. The wire at 6" to 8" away did not reach the 2000F it only got to 200F to 400F as evidenced by the insulation only melting this far back (depending on the insulation type pvc~200 teflon~400 iirc). The copper bus bar would have been at an even lower temperature and would probably not have gotten hot enough to be damaged.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[chicopee]

Any evidence of arcing? Sound that there is some resistance? Make sure all connections are tight and free of foreign material