lighting and conduit runs

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megloff11x

Senior Member
It's a bit out of my experience so I'll ask here. I was asked and didn't know the whole answer, and wasn't 100% sure of the bits that did ring a bell. Now I'll lose sleep until I know.

When you're calculating wire size & conduit needs for outdoor overhead lights (parking lots and parks/fields with illumination for night use):

1. What's the best or most used conduit material if you're going to bury it under the grass alongside or under the pavement of a lot or field? And what's the best insulation choice for the conductors? And how deep should you bury it?

2. I always get dyslexic on the bundling issue. If you need more wire than you have room for and have multiple conduit runs, how do you divvy up the various phases, neutral, and ground amongst the runs?

3. How much Voltage drop is allowed and how would you balance it if you have mutliple conduit runs?

4. You have to derate for temperature and bundling. Is it a good practice to consider the neutral a power carrying conductor to be on the safe side in case of the very likely harmonic or imbalanced load issues?

5. How is the tapping to the various lights usually handled where they go into the pole?

6. What's the best wiring plan to save on wire and have a good system? There's a park and parking lot, both with lights. the park has a perimeter and the parking lot will have lights throughout.

7. If you're using metal conduit, can/should it be used for the grounding or should you run a separate grounding conductor back to the main panel?

7. Am I missing any other considerations?

Some days I feel like the "Farside" kid whose brain is full. Other days I'm the one pushing on the door I should be pulling open...

Matt
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
It's a bit out of my experience so I'll ask here. I was asked and didn't know the whole answer, and wasn't 100% sure of the bits that did ring a bell. Now I'll lose sleep until I know.

When you're calculating wire size & conduit needs for outdoor overhead lights (parking lots and parks/fields with illumination for night use):

Some input on a few of your questions
1. What's the best or most used conduit material if you're going to bury it under the grass alongside or under the pavement of a lot or field? And what's the best insulation choice for the conductors? And how deep should you bury it?

95% of the jobs I see are PVC. A few folks will use GRS at the pole bases as they have experienced PVC being broken at pours.

2. I always get dyslexic on the bundling issue. If you need more wire than you have room for and have multiple conduit runs, how do you divvy up the various phases, neutral, and ground amongst the runs?

Keep in mind 300.3(B). The phases and those associated neutral and equipment ground must share the same conduit.
3. How much Voltage drop is allowed and how would you balance it if you have mutliple conduit runs?
VD consideration by Code is a FPN and not mandatory. Al tough 3% is a good goal, you really need to keep in mind the voltage operating range of the ballast being used. VD in excess of 3% may not be a REAL issue.
4. You have to derate for temperature and bundling. Is it a good practice to consider the neutral a power carrying conductor to be on the safe side in case of the very likely harmonic or imbalanced load issues?
Normally, "upsizing" of conductors for VD makes this a "non-issue". Few lot lighting jobs I see even have a neutral.
5. How is the tapping to the various lights usually handled where they go into the pole?
Normally see that done in the base (handhole area). Some think it's productive to add in-line fusing as supplemental OCP to prevent multiple fixture outage on one ballast shorting. The circuits normally allow #12 taps.
6. What's the best wiring plan to save on wire and have a good system? There's a park and parking lot, both with lights. the park has a perimeter and the parking lot will have lights throughout.

no input
7. If you're using metal conduit, can/should it be used for the grounding or should you run a separate grounding conductor back to the main panel?
Can be. I probably would not, but, I don;t recall seeing any large lighting projects with all metal conduit.

7. Am I missing any other considerations?

Some days I feel like the "Farside" kid whose brain is full. Other days I'm the one pushing on the door I should be pulling open...

Matt
 
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ericsherman37

Senior Member
Location
Oregon Coast
6. What's the best wiring plan to save on wire and have a good system? There's a park and parking lot, both with lights. the park has a perimeter and the parking lot will have lights throughout.

This kind of depends on the layout - every parking lot is different. Sometimes it depends on where the circuit source is located relative to the lights. You may be able to come out of the source panel and take off in two directions at once; other times it makes more sense to just daisy chain all the way around the lot.

Kind of a subjective issue.
 
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