Street lighting conductors and voltage-drop calculations

[RCBob]

This question concerns conductors for street lighting systems that use 120V, 240V, or 480V power. Can someone please confirm or correct my understanding as written below, and answer the questions?

120V/240V
For a 120V street-light system, conductors are (1) phase (hot), (1) neutral, and (1) bond. Current on the neutral conductor is the same as on the phase conductor, so for voltage-drop calculations and sizing conductors, use the sum of the lengths of both conductors, that is, the two-way distance.

For 240V street lights powered by 3-wire, 120/240V, single-phase power, conductors are (2) phase conductors plus a bond conductor. The phases of the two phase conductors are opposite and balanced, so there would be no current in a neutral conductor, so a neutral conductor is not used. A bond conductor is used. Questions:

1. Is one of the bond conductor?s possible functions to handle any unbalanced load that may occur?
2. Should the bond conductor always be the same gauge as the phase conductors?
3. Because there is no neutral conductor,a.Do voltage-drop calculations use the one-way distance?
   b. Do you cut that one-way distance in half because there are two phase conductors, which together have less resistance than a single conductor?

240V/480V
Let?s say that the power available is not 3-wire, 120/240V, single-phase, but instead 3-wire, 240/480V, single-phase. Are conductors similar to those described above? Specifically:
4.240V:

1. Conductors: (1) phase, (1) neutral, (1) bond?
2. Voltage drop calculations use two-way distance?

1. 480V:
   1. Conductors: (2) phase, (1) bond?
   2. Voltage drop calculations use one-way distance?
   3. Divide one-way distance by two because two conductors have less resistance than one?

Any help in confirming or correcting my understanding will be appreciated.

 

[Dennis Alwon]

For 240V street lights powered by 3-wire, 120/240V, single-phase power, conductors are (2) phase conductors plus a bond conductor. The phases of the two phase conductors are opposite and balanced, so there would be no current in a neutral conductor, so a neutral conductor is not used. A bond conductor is used. Questions
Is one of the bond conductor?s possible functions to handle any unbalanced load that may occur?

The bond you talk of is the equipment grounding conductor. This should only carry current in case of a ground fault. There should not be an inbalance in a 240V hookup with no neutral.

Should the bond conductor always be the same gauge as the phase conductors?[/QUOTE
No. The equipment grounding conductor is based on the overcurrent protective device and is sized based on T. 250.

Because there is no neutral conductor,a.Do voltage-drop calculations use the one-way distance?

No

 

[RCBob]

Thank you

Thank you

Dennis,
Thank you for your reply. This was my first post, and it was maybe too ambitious. I did not get it posted very clearly, and I can't find the icon that allows me to edit. So with apologies, I re-post the bottom part:

For a 240V circuit from a 240/480 transformer:
Would the conductors be (1) phase, (1) neutral, (1) bond?
Would voltage drop calculations use the two-way distance?

For a 480V circuit from a 240/480 transformer:
Would the conductors be (2) phase, (1) bond?
Do voltage-drop calculations use the one-way distance?
Do you divide the one-way distance by two because two conductors have less resistance than one?

Thank you