Reactance values in Table 9 of NEC--what if only two conductors are carrying current?

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Table 9 of NEC says: "Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz, 75?C (167?F) ? Three Single Conductors in Conduit"

Are the reactance values given in the table valid only if all three conductors are carrying current? What if one of the conductors is not carrying any current? And how about if one of the conductors is carrying more current than the other?

Could the reactance values given in the table be still be used in the cases I've mentioned?

 

[GoldDigger]

Table 9 of NEC says: "Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz, 75?C (167?F) ? Three Single Conductors in Conduit"

Are the reactance values given in the table valid only if all three conductors are carrying current? What if one of the conductors is not carrying any current? And how about if one of the conductors is carrying more current than the other?

Could the reactance values given in the table be still be used in the cases I've mentioned?

The reactance values (which are per wire) will be close enough as long as the entire circuit (out and return) is in the same raceway and the current carrying wires are reasonably close.

If (as not generally allowed by Code) you had only one current carrying wire in the raceway, then the inductance value would be larger than shown in the table. Same if you had knob and tube with a wide spacing between the current carrying wires.

 

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Yes, there is one complete circuit in the raceway (one phase conductor, one neutral conductor) but there is a third conductor with no current in it.

So in this case would we use the reactance values for two conductors in raceway (if we know them) and disregard the third conductor as if it is not there? The third conductor, even if it is non-current carrying, will have no effect on the overall reactance of the other two current-carrying conductors?

How about the case where there are three conductors in raceway but their currents are not the same?

 

[GoldDigger]

Yes, there is one complete circuit in the raceway (one phase conductor, one neutral conductor) but there is a third conductor with no current in it.

So in this case would we use the reactance values for two conductors in raceway (if we know them) and disregard the third conductor as if it is not there? The third conductor, even if it is non-current carrying, will have no effect on the overall reactance of the other two current-carrying conductors?

How about the case where there are three conductors in raceway but their currents are not the same?

The key point that influences the reactance of a single wire is where the magnetic field that is created by the current in the wire ends up.
If the return current corresponding to the current in wire A returns via wire B which is close (insulation thickness more or less) to wire A, then the inductance associated with wire A will be lower than if the same size wire A were in the open air.
If the return current corresponding to wire A is split (in any ratio) between wires B and C, the effect on wire A (reducing the inductance below the open air value) will be exactly the same.

So as long as the total current in the raceway is zero and all of the wires are in close proximity, you can go ahead and use the table value for each wire.
Say you have a single phase to phase load on a three phase 3 wire circuit.
The circuit inductance will be twice the table value for one wire since the complete circuit consists of two wires. Just as the resistance is twice that of a single wire. The third wire does not affect anything since it carries no current and generates no magnetic field.