NEC splicing question?

[rrc14]

Hello folks,

I have a 20A lighting circuit with an actual load of 15A. Due to the length of the circuit and voltage drop considerations I will need to use a 1/0 conductor to reduce the voltage drop. The 20A CB can handle up to a #4 conductor.

I'd like to use a #12 conductor from the 20A CB in the panelboard over to a junction box, where I'll splice the #12 to a 1/0 conductor. Then down the line I'd splice a #12 from the 1/0 conductor over to the light fixture.

Is this acceptable within the NEC?

Thanks,

 

[raider1]

Yes, what you are purposing would be NEC compliant.

Chris

 

[Pierre C Belarge]

Hello folks,

I have a 20A lighting circuit with an actual load of 15A. Due to the length of the circuit and voltage drop considerations I will need to use a 1/0 conductor to reduce the voltage drop. The 20A CB can handle up to a #4 conductor.


Thanks,

When increasing the size of the ungrounded conductor, the equipment ground conductor is required to be increased in size as well [250.122(B)].

For your circuit, the equipment ground conductor will also be required to be 1/0.

 

[SEO]

How long of a run are you going to install? Must be very long to require a 1/0.

 

[Dennis Alwon]

You can also just splice the 1/0 in the panel. I also am curious about the need for 1/0. What kind of lights are they and how long is the run - one direction?

 

[rrc14]

The length of the circuit is just over 1000'. The 120 volt circuit supports (6) 300W light fixtures. The first light fixture is about 700' away form the panelboard. I like the idea of splicing the 1/0 conductor inside the panelboard.

 

[480sparky]

I would look into seeing whether you could obtain similar luminaires in either a 208 or 240-volt, depending on the voltage available. You may find it's woth it in copper savings alone.

 

[augie47]

Are they incadescent fixtures ? If so, I could live a with a little more voltage drop and cut my cost a bit...but that's just me

 

[taylorp]

I am assuming that you are using 120 volts to feed this light? By my quick calculations, your circuit is a little over 1100 feet. Is this accurate? That is an exceptionally long run.

 

[Dennis Alwon]

I am assuming that you are using 120 volts to feed this light? By my quick calculations, your circuit is a little over 1100 feet. Is this accurate? That is an exceptionally long run.

Even at that length the entire load is not at the end of the line so the VD formula would not be using the entire distance with the entire load. It would be sectional and you could change wire sizes in the run itself. As Gus stated, if the load is incandescent that it would not hurt to have a higher vd drop then 3%

 

[Dennis Alwon]

I just did a quick calc and it seems like you could run the first 750' with a #6 copper, then change sizes every 50' or so. So, from 750-800' you could then use a #4, 800-850' you could use #3, from 850-900' you could run a #1, 900-950' you would use 2/0 and then use 3/0 the last 50'.

Again this is based on 3% drop. 120volts times 3%= 3.6 volt drop. Most 120 cir. usually deliver 123- 125 volts so even at 123 voltage delivery you are still at 119.4 volts at the last light.

The advantage to this is that a #6, the cheapest wire, is on the longest run. Big savings

 

[hardworkingstiff]

I've never priced/used a buck/boost transformer, but could it be used in this application to help?

 

[winnie]

A boost transformer is probably not a good idea, because the voltage drop is load dependent...if a lamp burns out, then the voltage will get higher and the other lamps will be stressed.

I would give strong consideration to a multiwire branch circuit; by putting only 7.5A on each half of the circuit, you halve the voltage drop on the 'hot' conductors and eliminate the voltage drop on the neutral. You could get away with 4#8 conductors rather than 3#1/0 conductors.

-Jon

 

[jim dungar]

I just did a quick calc and it seems like you could run the first 750' with a #6 copper, then change sizes every 50' or so. So, from 750-800' you could then use a #4, 800-850' you could use #3, from 850-900' you could run a #1, 900-950' you would use 2/0 and then use 3/0 the last 50'.

Your numbers do not make sense intuitively.

You have the largest amount of current flowing the the smallest size conductor for the longest distance, this would mean the largest voltage drops occurs in the first length of the circuit. I usually try to have the least voltage drop occur at the beginning of the circuit, although I admit that optimizing the $/ft sometimes requires creativity.

 

[wireguru]

for 1100ft of 1/0x3 for 15a @ 120v worth of load, I think I would put my money into a couple small transformers 480-120/240, and 3300ft of #10(or whatever is the right size).....

 

[Cow]

for 1100ft of 1/0x3 for 15a @ 120v worth of load, I think I would put my money into a couple small transformers 480-120/240, and 3300ft of #10(or whatever is the right size).....

I agree. I'd also take a hard look into higher voltage fixtures. 120v ran that far just isn't practical, who designs something like that?

 

[wireguru]

I agree. I'd also take a hard look into higher voltage fixtures. 120v ran that far just isn't practical, who designs something like that?

I just looked, and the transformers are cheap. $200 or less for 2kva, around $130 for 1.5kva..... I used a VD calculator, that comes back with #10... so I think 3300 feet of #10 and $300-$400 worth of transformers, and another $25 for secondary protection is going to be a WHOLE lot cheaper than 3300ft of 1/0, not to mention labor.....

 

[Dennis Alwon]

Your numbers do not make sense intuitively.

You caught it before I did. I woke up this morning realizing my error. Glad you got it.
I wouldn't mind help to see if this is correct. I assumed the first light at 750 from the source and the rest at 50' apart. I also approximated 3 amps per light

1/0 to the first light & 2nd light (800')
#1 to the third light (50')
#2 to the fourth light(50')
#4 to the fifth light (50')
#6 to the last light. (50)