Determining Conductors Per Phase: 451 Amps/ Ampacity

In summary, the number of conductors per phase can be determined by dividing the full load amperage by the desired wire size's ampacity, rounding up if there is a remainder. However, wire sizing may also be influenced by starting surges rather than just full load current.
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How do you determine the number of conductors per phase?

From my understand, the full load amperage divided by the desired wire size's ampacity rounded up if there is a remainder.

An example: If I have a 361 Full load Amp motor from the NEC table and I calculated the motor circuit conductor protection, which the specs of the motor 300 HP, 3 Phase, 60 Hz, 480V. 125 % x 361 Amps is 451 Amps. Which Amp would I chose to divide my desire wire? I would assume to use the 451 Amps for overload protection, but the calculations don't look right if I use 600MCM/kcmil wire.
 
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  • #2
Wire sizing is often dictated by starting surges, not full load current
 

1. What is the formula for determining conductors per phase?

The formula for determining conductors per phase is Amps/Ampacity = Conductors per phase. In this case, 451 Amps/Ampacity = Conductors per phase.

2. What is the meaning of Amps/Ampacity?

Amps/Ampacity is the ratio between the amount of current flowing through a conductor and the maximum amount of current that the conductor can safely carry without overheating. It is used to determine the number of conductors needed to carry a specific amount of current.

3. How is the Ampacity of a conductor determined?

The Ampacity of a conductor is determined by factors such as the material, size, and insulation of the conductor, as well as the ambient temperature and the method of installation. It is typically listed in a table provided by the National Electric Code (NEC).

4. Why is it important to determine the correct number of conductors per phase?

It is important to determine the correct number of conductors per phase to ensure that the electrical system is safe and functional. If there are not enough conductors, it can lead to overheating and potentially cause a fire. On the other hand, if there are too many conductors, it can be costly and inefficient.

5. What are some common factors that can affect the number of conductors needed per phase?

Some common factors that can affect the number of conductors needed per phase include the type of electrical load, the distance between the power source and the load, the type of conductor used, and the ambient temperature. It is important to consider all of these factors when determining the number of conductors needed.

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