120-volt light pole voltage drop

[onelilvictory]

Good morning all,

I have ran into an application that seems odd to me, but would like some input. I have a project that calls for (5) 120-volt, 400W quad pole fixtures on 25' poles. Each pole is shown on its own circuit. Distance to the first pole is 120', then 70' increments from there. The drawings show installing #8's from the building to the first pole for ALL 5 circuits. Then #10's to the next two poles for the next 4 circuits, and finally #12's to the last two poles for the final two circuits.

I know you can downsize the cable, but this application does not seem right to me since each pole is on it's own circuit back to the source. My calculation shows #8's to the first pole, first circuit, then all remaining to be #6's. Any thoughts?

Thanks,

 

[Eng]

I believe I understand your situation.

1st pole: 2*12.4*16.7*120'/3.6v = 13,805CM or #8's
2nd pole: " " *190'/3.6v = 21,858 or #6's
3rd pole: " " 260'/3.6v = 29,911 or #4's
4th pole: " " 340'/3.6v = 39,115 or #4's
5th pole: " "410'/3.6v = 47,168 or #3's

 

[kwired]

I think I see the problem you are getting at also.

Wondering if there is a good reason to not use a higher voltage, or at least use MWBC. 208 or 240 will definitely help with voltage drop 277/480 if readily available, even better.

Just using a 240 volt MWBC with the calculation posted in post #2 changes the need at the first pole to 10 AWG and you have 2 circuits taken care of instead of 1 using 3 conductors instead of 4. Throw in the distance to the second pole and you are a little too much for 10AWG so you may want to consider #8 but is still 3 conductors instead of 4.

 

[Eng]

I think I see the problem you are getting at also.

Wondering if there is a good reason to not use a higher voltage, or at least use MWBC. 208 or 240 will definitely help with voltage drop 277/480 if readily available, even better.

Just using a 240 volt MWBC with the calculation posted in post #2 changes the need at the first pole to 10 AWG and you have 2 circuits taken care of instead of 1 using 3 conductors instead of 4. Throw in the distance to the second pole and you are a little too much for 10AWG so you may want to consider #8 but is still 3 conductors instead of 4.

I agree, why in the world are you running 120V this great of a distance? Is 208/240/277/480 not available?

 

[kwired]

I agree, why in the world are you running 120V this great of a distance? Is 208/240/277/480 not available?

If 120 volt is available it is likely there is either 208 or 240 also easily available.

 

[onelilvictory]

If 120 volt is available it is likely there is either 208 or 240 also easily available.

Yes 208 is available, but this is a project that I inherited and the lighting was already released. Luckily, I was able to change the voltage yesterday to 208 without incurring any cost increase.

My original question though was in reference to the voltage drop calculation that the individual designed it to. To clarify, take pole #5 which is the farthest away. It will have 16 amps on it at an overall distance of roughly 350'. This persons design is cascading that circuit starting with #8's from source to 1st pole, then #10 from pole 2 to 3, and finally #12 from pole 4 to 5. I thought you could only do that if say there were multiple fixtures on a circuit and you were dropping load from pole to pole.

 

[augie47]

Yes 208 is available, but this is a project that I inherited and the lighting was already released. Luckily, I was able to change the voltage yesterday to 208 without incurring any cost increase.

My original question though was in reference to the voltage drop calculation that the individual designed it to. To clarify, take pole #5 which is the farthest away. It will have 16 amps on it at an overall distance of roughly 350'. This persons design is cascading that circuit starting with #8's from source to 1st pole, then #10 from pole 2 to 3, and finally #12 from pole 4 to 5. I thought you could only do that if say there were multiple fixtures on a circuit and you were dropping load from pole to pole.

I would say from an NEC standpoint, as long as your smallest conductor has the proper overcurrent protection you are compliant. The NEC has no actual voltage drop requirement for the most part (exceptions are Art 647,695 ). If the cascading wire sizes satisfy the design, there would be no NEC violation.

 

[kwired]

If you cascade the circuit as you describe you would still have to calculate each segment separately to find the drop on each segment and the sum of the drops is what you would have at the load.

As Augie said voltage drop is not required to be corrected by NEC. It may be a good idea for some equipment to consider it though. How much it needs corrected is also another issue. I ran a circuit for X-ray equipment at a small hospital one time. I don't remember what the voltage drop specifications were anymore but the conductors were pretty large for no more load than they were carrying. You have to realize they wanted a limited amount of voltage drop even during the inrush of energizing transformers in the x-ray equipment.

 

[defears]

It just sounds like the circuit was originally designed for 1 208 volt circuit and then changed to 5 120 volt circuits and no plan check.

BTW, I've installed similar setups (120 volt) in the past because the owner wanted outlets for X-mas lights on the pole also.

 

[kwired]

Good morning all,

I have ran into an application that seems odd to me, but would like some input. I have a project that calls for (5) 120-volt, 400W quad pole fixtures on 25' poles. Each pole is shown on its own circuit. Distance to the first pole is 120', then 70' increments from there. The drawings show installing #8's from the building to the first pole for ALL 5 circuits. Then #10's to the next two poles for the next 4 circuits, and finally #12's to the last two poles for the final two circuits.

I know you can downsize the cable, but this application does not seem right to me since each pole is on it's own circuit back to the source. My calculation shows #8's to the first pole, first circuit, then all remaining to be #6's. Any thoughts?

Thanks,

Please clarify: do you have 5 fixtures per pole or just 5 poles with one fixture each?

 

[onelilvictory]

Please clarify: do you have 5 fixtures per pole or just 5 poles with one fixture each?

There are (5) poles with one head on each pole. Funny thing is now they are uping the fixtures to 1000 watt heads and added two more poles. Praise the Lord for change orders! This will help me be able to do my own design on the circuit and propose some outlets on the poles for Christmas lighting! (Which I found out after the fact was the reason they wanted 120V poles)

Thanks to all for the help. It's nice to know there is a place we can go for some good technical advice when needed.

 

[onelilvictory]

There are (5) poles with one head on each pole. Funny thing is now they are uping the fixtures to 1000 watt heads and added two more poles. Praise the Lord for change orders! This will help me be able to do my own design on the circuit and propose some outlets on the poles for Christmas lighting! (Which I found out after the fact was the reason they wanted 120V poles)

Thanks to all for the help. It's nice to know there is a place we can go for some good technical advice when needed.

Actually, I mis-spoke above. There are (5) poles and each pole had (4) fixtures on it. Sorry, hadn't had that first cup of coffee yet...:blink:

 

[Smart $]

... This will help me be able to do my own design on the circuit and propose some outlets on the poles for Christmas lighting! (Which I found out after the fact was the reason they wanted 120V poles) ...

Don't forget to include the Xmas lighting in your Vdrop calc's...