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Friday, September 20, 2019
Question:
In table 9 of the NEC there are 2 values that are used for R for example; I go to #10 wire, then the column for .85pf, then to steel conduit and the R values are 1.1 and 3.6. I have always used the 1.1 for my calculations but what is the top value used for?
Arthur Retana
A
Answer:
Hey Arthur thanks for your question. Although possibly not as clear as it could be the top value is ohms to neutral per kilometer and the bottom value is ohms to neutral per 1000 feet as indicated in the sub-heading of the table. There is about 3281 feet in a kilometer so the top value is about 3.281 times the bottom value. If you are using 1000 feet as your base then you are using the correct value.