voltage drop

[Smart $]

sorry gar,you of course are correct, I mentally do combine the power equation with ohms law, I guess so I can keem them in my memory together. I=er and P=ie

Its I=E?R...

Or rather E=IR

If you do word association, start with "hair" "pie"... then spell it "HEIR" "PIE", with the silent H as a clue to exclude.

 

[kwired]

Its I=E?R...

Or rather E=IR

If you do word association, start with "hair" "pie"... then spell it "HEIR" "PIE", with the silent H as a clue to exclude.

I learned it as PIE, and

Old McDonald had a farm ..EEE, III... EEE, III... ohms.

I guess it worked, I still remember it.

 

[calvin1]

hmm hair pie should be able to remember that one!

 

[ptonsparky]

hmm hair pie should be able to remember that one!

Ohms law will never be the same

 

[kingpb]

I know at least one electrical engineer who just shudders at the use of 12.90 for a K value for copper, because it is not an absolute, but varies from one size conductor to another. For practical purposes of estimating voltage drop, the electrical industry has pretty much standardized on the average K values of 12.90 for copper and 21.20 of aluminum.

I don't use it either. The international standard for conductivity is that of annealed copper. Commercial hard drawn copper and aluminum is less than annealed. I think better values to use are copper; 10.7(ohms-cmil/ft) and aluminum; 17.0 (ohms-cmil/ft). What is also important is that theses are values determined at 20 Deg C.

For other temperatures the effective resistance would have to be adjusted. Going from 20 deg C to 30 deg C, You can consider an approx. increase of 4% for hard drawn copper and aluminum. Keeping in mind that Table 8 of NEC is based on 75 deg F, which is about 24 deg C and 310-16 ampacities is based on 30 deg C.