How do you determine the number of conductors per phase?

Answer 1

The number of conductors is simply the service amperage divided by the desired wire size's ampacity rounded up if there is a remainder. Example: 1000A service, using 300kcmil conductors at 75 deg C: 300kcmil ampacity in this situation is 285. 1000/285=3.5 Since you can't have 3.5 conductors, you must round up to 4. This would give you a total ampacity of 285A x 4, or 1140A. If you're rounding farther than necessary, such as in this case, you can try using the next smallest conductor and adding another set to closer match your required ampacity. 250kcmil ampacity is 255. 1000/255=3.92 We will also round this up to 4, but we aren't rounding as far as the earlier example. The total ampacity is now 1020. 250kcmil x 4 sets is probably the best arrangement for this 1000A service. You could use larger wire and fewer sets, but smaller wire is more cost effective for both ampacity per pound and labor costs for installation.

Answer 2

The number of conductors per phase depends on the type of electrical system being used (e.g., single-phase or three-phase) and the specific application requirements. In general, for balanced three-phase systems, there are typically 3 conductors per phase. However, for single-phase systems, there is usually 2 conductors per phase.

Answer 3

It depends on the maximum current to be supplied. Wire tables give the maximum current (ampacity) that wires of different sizes can take. For permanent installations with constant load current it is common to limit the current to around half of the values give in the tables, because an appreciable temperature rise means significant power losses.

Answer 4

To calculate the wire sizes for the feeders for motors you have to know the motor's full load amperage which can be determined from the motor nameplate.