Ground conductor sizing following IEEE 80-2000

[radug]

Hello,

I have some doubts with ground conductor sizing with IEEE 80-2000 equations.
-Material parameters of table 1 give copper soft-drawn and copper hard-drawn (commercial). If stranded copper soft-drawn with Class B is used, which are its parameters?
-In some specification I found "soft drawn bare stranded copper strand Class II". What is Class II?
-When selecting the maximum temperature, data is given about fusing temperature of copper, but then if mechanical connections are used, both 80-2000 and 837 recommend 250ºC.
What maximum temperature should be used if all the connections are going to be Cadwell type?

Thanks.

 

[jghrist]

The characteristics given in Table 1 do not depend on stranding, so you need to use the characteristics of soft-drawn copper.

I don't know what Class II refers to, but I wouldn't worry about it. Class B refers to the stranding.

You can use the fusing temperature of the conductor if you are using Cadweld connectors.

 

[radug]

Thanks jghrist,

Is there any standard which explicitly says that with Cadwell the fusing temperature of copper can be used?

I usually took hard-drawn values because they were more conservative and also because of the word "commercial". I think stranded soft-drawn copper is not 100% IACS, but I am not sure.

If all the grounding mesh is done with cadwell or exothermal weldings, but for equipment grounding through grounding stingers is done with mechanical connections, can the grounding mesh be calculated with the fusing temperature but then calculate the wire cross-sections of the stingers or other connection wires with 250ºC, for example needing 120mm2 for the ground mesh but 185mm2 for those grounding stingers, or the connection would not be able to withstand the fault currents?

 

[jghrist]

I think that this came from the 1986 revision of IEEE std 80, but I don't have a copy of the old standard to check.

IEEE std 80-2000 doesn't specifically say that mechanical connectors have to have a lower temperature limit. It says that connectors should be massive enough to maintain a temperature lower than that of the conductor and to withstand the effect of heating.

I think the difference between the two commercial hard-drawn values in Table 2 is to account for the possible reduction in strength of the conductor per 11.3.3 b).