Overhead feed to a work shop

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bakerboy9999

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I’m a commercial electrician trying to help a buddy out with a residential project. I’m trying get some answers in the code for him but struggling a bit hoping you all can help point me in the right direction.
His main house sits up on a hill with a 200a service.
He is installing a pre-ordered metal structure ( work shop) on his property Roughly 180’ from main panel. He wants to feed the work shop with 100a feed. To accomplish this , he would run about 80’ through his attic in conduit, punch outside and set a disco. Install a riser so he can feed overhead(free air) down the step embankment to the new workshop.
What I can find
- required GES at new building 250-32(a)
-EGC required between buildings (4-wire feeder) 250-32 (b)(1)
- 100 amp at 180’ with max 3% loss, #1 awg.
What I cant find-
Can he feed his work shop with an overhead feed?
If he runs emt threw the attic to his disconnect with #1 awg then transitions to an overhead feed, what type of wire and size would be required going free air to his work shop?
any help and or advise is greatly appreciated.
 
bakerboy9999 said:
I’m a commercial electrician trying to help a buddy out with a residential project. I’m trying get some answers in the code for him but struggling a bit hoping you all can help point me in the right direction.
His main house sits up on a hill with a 200a service.
He is installing a pre-ordered metal structure ( work shop) on his property Roughly 180’ from main panel. He wants to feed the work shop with 100a feed. To accomplish this , he would run about 80’ through his attic in conduit, punch outside and set a disco. Disconnect not required at this location, but not prohibited either. Install a riser so he can feed overhead(free air) down the step embankment to the new workshop.
What I can find
- required GES at new building 250-32(a) yes
-EGC required between buildings (4-wire feeder) 250-32 (b)(1)yes
- 100 amp at 180’ with max 3% loss, #1 awg. didn't verify - is this copper or aluminum?
What I cant find-
Can he feed his work shop with an overhead feed?yes
If he runs emt threw the attic to his disconnect with #1 awg then transitions to an overhead feed, what type of wire and size would be required going free air to his work shop?Whatever you decide is necessary for voltage drop is likely larger than minimum required conductor.
any help and or advise is greatly appreciated.
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replies in line with quote
 
3% voltage drop is not a requirement in the code. I would look at the expected load and what it could tolerate (unless he has money to burn).
 
Appreciate the info. It would be copper. I’m familiar with running thhn or thwn in conduits but once he transitions to open air, I’m unsure what type he should use. I know it needs to be sun light resistant but can it be a smaller size wire seeing it’s free air and not in conduit?
If he runs #1 up the riser and out the weather head at both ends, would the wire running free air need to match in size or could it be smaller due to free air?
 
Barbqranch said:
3% voltage drop is not a requirement in the code. I would look at the expected load and what it could tolerate (unless he has money to burn).
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Understandable. I was going off the fact he wanted a 100 amp panel in the work shop. My understanding is in general you don’t want to exceed 3% drop so going with what I had at the length of 180’ , it came out to #1 in conduit. I’m just confused once it transitions to open air. Type of cable and size?
 
For the overhead cable, you'll need AL quadraplex. Most overhead cable is not listed, it will take some hunting to find listed cable.
 
bakerboy9999 said:
Appreciate the info. It would be copper. I’m familiar with running thhn or thwn in conduits but once he transitions to open air, I’m unsure what type he should use. I know it needs to be sun light resistant but can it be a smaller size wire seeing it’s free air and not in conduit?
If he runs #1 up the riser and out the weather head at both ends, would the wire running free air need to match in size or could it be smaller due to free air?
Click to expand...
Conductor in free air may have higher ampacity than in raceway. Voltage drop is still dependent on cross sectional area and is why I said if you are upsizing for VD to begin with, you will have plenty of conductor when it comes to min ampacity and overcurrent protection level. Your 1 AWG copper could be 3 AWG copper for a 100 amp circuit if you weren't factoring in VD.
 
tom baker said:
For the overhead cable, you'll need AL quadraplex. Most overhead cable is not listed, it will take some hunting to find listed cable.
Click to expand...
Is there info out there that shows what distance required additional support? For his situation he’s going 100’ free air down a step embankment. He’s running ACSR. It shows 100’ weights 60 lbs and breaking force of 4300lbs. I can’t imagine a situation he would encounter that would put that amount of force on the cable. But I also can’t find any info on what distance would require an additional support.
 
bakerboy9999 said:
Is there info out there that shows what distance required additional support? For his situation he’s going 100’ free air down a step embankment. He’s running ACSR. It shows 100’ weights 60 lbs and breaking force of 4300lbs. I can’t imagine a situation he would encounter that would put that amount of force on the cable. But I also can’t find any info on what distance would require an additional support.
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It’s complicated. Start with the catenary equation. The amount of sag you can tolerate based on the minimum height will determine the tension in a static condition. Then you have to factor in external loading from weather conditions, etc.
I would think the cable companies would have some guidelines to save you from having to engineer this from scratch.
 
bakerboy9999 said:
Is there info out there that shows what distance required additional support? For his situation he’s going 100’ free air down a step embankment. He’s running ACSR. It shows 100’ weights 60 lbs and breaking force of 4300lbs. I can’t imagine a situation he would encounter that would put that amount of force on the cable. But I also can’t find any info on what distance would require an additional support.
Click to expand...
Depends on what weather factors typically will come into play, and how tight it will be tensioned.
 
tom baker said:
For the overhead cable, you'll need AL quadraplex. Most overhead cable is not listed, it will take some hunting to find listed cable.
Click to expand...
Utility or lineman shop can quote quadruplex between buildings, or triplex from pole to separate shop meter.

Utility electrical requirements, and NEC 215 & 230 allow building as support, to avoid large wire in raceways, or having to set another power pole.
 
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