wire sizing
- Thread starter ilss
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jtester
Senior Member
- Location
- Las Cruces N.M.
That is not a difficult thing to calculate. As a designer, I'd encourage you to learn that skill. Give the calculation for one size motor a try and post your results.
Jim T
Jim T
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
To that let me add that the information you seek is not to be found in one single table. You need to figure out the required ampacity of the conductors, on the basis of motor horsepower and rated voltage. There are rules related to up-sizing the conductor, depending on the size of the motor or the size of the largest motor, if you have more than one motor fed from the same conductor. Then you look for conductors that have that required ampacity.
Not everything can be reduced to a "table". Motors and service calculations involve multiple steps and multiple code references. Spend some time in article 430 and the examples in the back of the book and you should be able to figure it out. You will then need to factor in voltage drop if your circuit lengths are excessive. Oh, and throw away that copy of the 1995 code and get the current edition. There have been alot of changes in the past decade!
jeff43222
Senior Member
- Location
- Minneapolis, Minnesota
If you find one, let me know. I've been working on sizing conductors for motors for the last few days.
T430.250 is a good place to start, but 430.122(A) comes into play if the motor has an adjustable-speed drive. Then you get to contact manufacturers to get their catalog data. Then the PE in the next cube starts talking about harmonics and whether they are included in the rating, so that complicates things.
You also have to refer to 310.16-19, depending on what kind of conductor you are using under what conditions. None of this takes into account derating the conductors due to ambient heat or having more than three current-carrying conductors in a raceway. After all this, you can calculate voltage drop and increase the size of your conductors accordingly.
I have no idea how all of this could be distilled down to a single table.
T430.250 is a good place to start, but 430.122(A) comes into play if the motor has an adjustable-speed drive. Then you get to contact manufacturers to get their catalog data. Then the PE in the next cube starts talking about harmonics and whether they are included in the rating, so that complicates things.
You also have to refer to 310.16-19, depending on what kind of conductor you are using under what conditions. None of this takes into account derating the conductors due to ambient heat or having more than three current-carrying conductors in a raceway. After all this, you can calculate voltage drop and increase the size of your conductors accordingly.
I have no idea how all of this could be distilled down to a single table.
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