Bare Copper Wire for Grounding

[BigH]

I hope that I am in the right forum for this. Apologies if not. Working in Indonesia and our electrical guy comes up to me and asks some questions on bare copper grounding wire. What is the difference between hard drawn or soft drawn - and how to tell difference in the field? (remember I am a geotechnical engineer). Secondly, I understand diameter in mils, but what does Circular mil area mean (in cmils) and size in kcmil? I have my "feeling" given 7-strand reinforcing for concrete but . . . Your help is greatly appreciated - our electrical guy has already lost half a kilo in worry. . . .

 

[dbaird]

Link:

http://en.wikipedia.org/wiki/Circular_mil

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[jeezlouise]

Soft drawn copper (or annealed copper) has a lower breaking strength than hard drawn copper, however, it does have lower resistivity. Use the soft drawn for your ground wire. Use hard drawn for long overhead lines that require higher strength. You probably won't know the difference in the field unless you have a sample of both in the same gauge. Burying copper in concrete for grounding whether soft drawn or hard drawn is perfectly acceptable and is common practice. Just make sure your concrete mix doesn't have a high sulfur content (causes corrosion). Also make sure the grounding conductor is of sufficient size to handle the available fault current. There are Tables in the American National Electric Code (NFPA 70) for sizing.

 

[oldfieldguy]

And bring in your corrosion prevention people in for the discussion. We have a running argument about bare copper ground grids making those nasty ol' steel pipelines sacrificial to my grounding system.

old field guy

 

[jghrist]

The reason for using soft drawn is the ability to bend it easily. It's a lot easier to work with in grounding and the strength of hard drawn isn't needed.

 

[davidbeach]

A circular mil is the cross sectional area of a conductor with a diameter of one mil. Typically used in conjunction with AWG size for conductors larger than 4/0 (0000), the largest size defined in the AWG system.

 

[Marmite]

It's quite common to use lengths of recovered copper overhead line conductor for earthing if its available as its an efficient use of something that would likely end up in the scrap. Overhead line conductor is hard drawn and most people would struggle to bend anything other than the smallest sizes by hand. If you are buying new, go for soft drawn.
Regards
Marmite

 

[BigH]

Terima kasih (thank you) for all your responses. Appreciate it!