voltage drop 425 feet help

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Deanos

Member
Location
Ct
Ok here is the thing, pipe is existing 1&1/2 pvc 425 feet long 60 a overcurrent at the main panel,, the load at the barn is about 48 amps as a guess. Whats the largest size copper conductors and or alr. conductors that can be pulled?? So far I came up with 3 3/0 alr. with no ground, drive a ground rod at the barn and call it a day, or three number 1/0 and one # 6 copper. What do you guys think?? The huge issue is the 1&1/2 pvc thats undersized.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
A lot of the guys on here post, or at least read, ET.
I definitively understand "bad days", but, if I may be so bold, I think an apology to Dennis in ET might well enhance the number of replies here.
It does appear you got some good answers there including reducing the neutral and I think it was clear that eliminating the equipment ground would be a violation of 250.32(B) so I'm unsure why you still look at that option unless you are simply seeking an answer that you like :D.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
A lot of the guys on here post, or at least read, ET.
I definitively understand "bad days", but, if I may be so bold, I think an apology to Dennis in ET might well enhance the number of replies here.
It does appear you got some good answers there including reducing the neutral and I think it was clear that eliminating the equipment ground would be a violation of 250.32(B) so I'm unsure why you still look at that option unless you are simply seeking an answer that you like :D.

another forum?
 

Deanos

Member
Location
Ct
I sent him a pm

I sent him a pm

And I do apologize, this last couple jobs are making me wanna jerk the wheel into the bridge abutment on the way home ! Ha!
 

Deanos

Member
Location
Ct
Grounds

Grounds

We're still on the 05 and I disagree on the ground issue. I think I can run two 3/0 and drive two rods at the barn and call it a day. No?
 

kwired

Electron manager
Location
NE Nebraska
Ok here is the thing, pipe is existing 1&1/2 pvc 425 feet long 60 a overcurrent at the main panel,, the load at the barn is about 48 amps as a guess. Whats the largest size copper conductors and or alr. conductors that can be pulled?? So far I came up with 3 3/0 alr. with no ground, drive a ground rod at the barn and call it a day, or three number 1/0 and one # 6 copper. What do you guys think?? The huge issue is the 1&1/2 pvc thats undersized.

I have no idea what was posted in ET, I rarely go there - they are too rude for me.

That said nobody can answer question as it was asked here without first knowing 1 - the voltage (though 120/240 single phase is kind of assumed), 2 how much voltage drop is to be allowed, and 3 what the real max load is, you said 60 amp overcurrent device, so we can go worst case scenario based on 60 amps, or we can go with a little more reality and go on actual load which was suggested to maybe be 48 amps.

Without doing any calculations the 3/0 seems like overkill to me, but again what is the allowable voltage drop? I ran a circuit to x-ray equipment in a hospital one time and they did want pretty low voltage drop and it was much larger conductor than I would have used for most other applications at the same load.
 

cadpoint

Senior Member
Location
Durham, NC
I think your falling short on the assumed * AMPS that will be used but lets assume 120/240.

50 Amps 350 kcmil XHHW 2 1/2" PVC sch 40 4-wire under 3% VD

50 Amps 4/0 CU XHHW 2" PVC Sch 40 4-wire under 3% VD

* You should probably load this up to 60 Amps. I only gave you 50A.

You need to find out all that is going into the Barn, sometimes they turn this place into
a very comfortable place, Office, Bath room, Hot-water.

Then just consider the standard stuff like Heat, A/C, even a motor for a barn fan, lights inside and out, then the real equipment like a welder, car lifts, Receptacle circuits, Etc., Etc., future

Bottom line you have to state you need to know exactly what's going in there, because your
suppose to do load calcuations that account for all the equipement, or worse future stuff.
that this install gets into.

Beside at this distance the price of wire and a transformer in barn might be a real option!
Which gets back in types of loads - equipment.

You don't want to embarass them or yourself in this matter.

Welcome to the Forum.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
We're still on the 05 and I disagree on the ground issue. I think I can run two 3/0 and drive two rods at the barn and call it a day. No?
NO!
Whether or not two ground rods with no EGC is compliant with your code, it would not be safe since it would not provide a low enough resistance in the fault clearing path to trip a breaker. You not only need an EGC, you need to upsize it by the same amount as you upsize the circuit conductors if you go to larger wire for voltage drop reduction.

If the cost of putting in a larger pipe is prohibitive, you really should consider running 480 with a transformer at each end.
You will save money on the wire and avoid a tight pull.
Is there an intermediate pull point you can use or will you have to go the 425 feet in one pull? Is the inside of the existing 1-1/2 inch PVC intact and clean?
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
I think your falling short on the assumed * AMPS that will be used but lets assume 120/240.

50 Amps 350 kcmil XHHW 2 1/2" PVC sch 40 4-wire under 3% VD

50 Amps 4/0 CU XHHW 2" PVC Sch 40 4-wire under 3% VD

* You should probably load this up to 60 Amps. I only gave you 50A.

You need to find out all that is going into the Barn, sometimes they turn this place into
a very comfortable place, Office, Bath room, Hot-water.

Then just consider the standard stuff like Heat, A/C, even a motor for a barn fan, lights inside and out, then the real equipment like a welder, car lifts, Receptacle circuits, Etc., Etc., future

Bottom line you have to state you need to know exactly what's going in there, because your
suppose to do load calcuations that account for all the equipement, or worse future stuff.
that this install gets into.

Beside at this distance the price of wire and a transformer in barn might be a real option!
Which gets back in types of loads - equipment.

You don't want to embarass them or yourself in this matter.

Welcome to the Forum.
Where you come up with your figures? I only come up with needing a 2/0 aluminum conductor if the load is 50 amps to get less than 3% drop from 240 volts. But unless there was a requirement to have less than 3% I likely would size to around 5%. You will still have some short term dips for motor starting, but unless they were not able to be tolerated so what, trying to eliminate those short term dips would mean pretty large conductors - and the source would also need consideration or there may still be some problems with motor starting.
 

kwired

Electron manager
Location
NE Nebraska
I did quick cost comparison - all aluminum conductors:

120/240 volts - 2 #2/0 AWG and 2 #3 AWG would cost about $1080

480 volts - 2 conductors and an equipment ground - all three #4 AWG would cost about $370

conductor cost difference is about $710 difference between 1.25 and 2 inch schedule 40 would be about $130 -

so about $840 difference - can you install two transformers and additional needed items for that cost or less?

Looking at needing 15 kVA transformers to handle 50 amps @ 240 volts Automation Direct has a 15kVA for $869 and you would need two of them. Increased conductor size looks like the way to go to me on this one - plus you don't have any core losses from the transformers.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
...difference between 1.25 and 2 inch schedule 40 would be about $130....
My impression from the OP's posts is that he has an existing 1.5" PVC in place underground, so the cost of switching to 2" would be a lot more than $130. :)
So he strongly favors something that will fit in that pipe.

As noted in another question on estimating/bidding, the cost of PVC installed in a trench is a lot higher than the price per foot of the material.
 

kwired

Electron manager
Location
NE Nebraska
but the 1.5" conduit is already run and buried.
I did miss that part, still depends on how much voltage drop can be tolerated, as you can get pretty good sized conductors in 1.5" conduit (for only 50 amps of load) my 2/0 aluminum mentioned before may fit -especially if compact conductor, I just threw in 2" as that is what I likely would have ran even if pulling the #4's, but out here on the farms it is usually 2 inch DB thinwall pipe (and we have already debated if that is acceptable in the past) and pull direct bury rated conductors through it. The pipe is seen more as gopher protection than it is seen as necessary to have conductor in a raceway, especially in loose soils where gopher activity is more common, or anywhere there is a food source present like grain storage and feed mill areas.
 
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