Feeder size

[rjprice]

The details: 40x60 barn. I Want 100A panel, 525ft from newly installed meter rack. What size aluminum feeder and how many conductors and will it fit in a 2" conduit?

also, if I have a ufer ground at the barn do I need to run a ground from the meter rack?

My sparky says 250mcm will work with just under 5% voltage drop.

 

[sberry]

Is there a disconnect at the meter?

 

[pattenp]

I'll assume this is coming off a disconnect at the meter so the feeder needs to be 4 wires. Using 250MCM with the needed sized equipment ground depending on the wire type may exceed the fill limit for 2" conduit. Looks like XHHW-2 with compact conductors will work in 2" conduit, otherwise I think you need 2.5" conduit.

The 250MCM is about as small as you should go for the distance.

 

[theoldwizard1]

The 250MCM is about as small as you should go for the distance.

Even if the OP drops his current requirements to say 60A ?

 

[pattenp]

Even if the OP drops his current requirements to say 60A ?

250MCM minimum is based on 100A. So what do you think dropping to 60A would do to the size of the feeder?

 

[wyliesdiesels]

What are your loads?

 

[sberry]

Also at 500 ft a 2 1/2 would get small, a 3 doesn't cost much more but,,, I may even be tempted to do direct burial depending on conditions.

 

[rjprice]

Sorry, yes there is a disconnect. Also, I may have messed up in that I poured 2 2" PVC sweeps into the corner of my slab for the feeder. If I have to have larger than 250MCM, can I put say two conductors in each 2" conduit or do they have a sheathing around them?

My loads are Air compressor (20A), tig welder (40A), mig welder (21A), lights (LED) and plugs. No AC/water heat. The welders will not be run at the same time.

As for conductor size, I have 246v at the disconnect and the sparky calculated just inder 5% voltage drop using 250MCM which he says still gives me ~233v at 525ft. He said that 400MCM would give me ~3% drop at that distance. Would you upsize the wire/conduit to go for 3%?

Thanks!

 

[bjcouche]

OK, I'll bite and grab my calculator...

In your case you cannot split the conductors between two different conduits. However if I am understanding correctly, you only placed a 2" sweep through your concrete and into a trench right? That means you still need to dig a trench and lay the rest of the 500+ feet of conduit, assuming you are not going with direct burial, but instead aluminum conductors in conduit. Direct burial is fine, my preference is conduit though.

Voltage drop calculation:
for 100A (((0.0847/1000)*(525*2))*100)/240 = 3.7%
for 90A that's 3.3%
for 80A that's 2.9%
The 0.0847 is the resistance of 250MCM aluminum per 1,000ft per chapter 9 table 8 of the NEC.

Unless your AHJ has specific requirements, the NEC only gives guidelines, not requirements for voltage drop. Usually 3% up to your breaker box, and a total of 5%. The additional 2% would be from your breaker box to a distant outlet. So 250MCM aluminum get's you in the ballpark at 100A, but based on your shop size and listed loads, I'd say you don't need anywhere close to 100A, certainly less than 80A. At 80A you'd be under 3%.
Here's what I'd do, size the breaker for 100A, and if you ever do need between 80-100A, you'd just have more voltage drop.
For the wire sizing, I'd use individual aluminum THWN conductors in conduit consisting of 250mcm-250mcm-2/O-1awg. The 2/O would be the neutral and the 1 would be the ground. There's not much need to oversize the neutral so drastically since it only carries the unbalanced load. Technically, the neutral could be reduced, down to 1awg but no smaller. The ground CANNOT be smaller than 1awg because it must be sized UP from 6awg proportionately as the line conductors were oversized.
The wire areas of compact THWN aluminum conductors from chapter 5 table 5A for 250mcm-250mcm-2/O-1awg would be: 0.353+0.353+0.192+0.1352=1.0332in square. That fits in 2" SCH 80 PVC conduit which allows up to (40% fill) 1.150in2.

Brian

 

[bjcouche]

There are a few other things to consider.
500+ feet is a long ways to be pulling wire through 2" conduit, So, as soon as the sweep exits the concrete underground, I would transition to 2.5" conduit. The trick there is that you need to pull the wire from the small diameter to the large diameter conduit to prevent chafing the wire at the transition. Another gotcha is that the lugs on 100-125A rated breaker boxes will not accept 250MCM wire, likely only up to 2/O. Since you have a disconnect at your "meter rack" I'm also assuming that's where your 100A breaker would be installed. If that's the case then you can use a 200A breaker panel in your shop and it will accept your 250MCM cable. The 200A breaker would just then be labeled something like "Disconnect switch" "100A Service". If you've already purchased a 125A panel, then you could simply add a splice box inside your garage to transition down to a smaller wire size to fit your lugs.
If you want to do direct burial, then you can't use my wire suggestions, as THWN is not rated for direct burial. You are stuck using the multi-conductor "mobile home" cable sizes that are rated for direct burial. That comes in 4/O-4/O-2/O-4awg and 4/O-4/O-4/O-2/O. However, neither of these will legally fit in your 2" conduit sweep. Although the individual wires have a smaller ampacity, they have an overall larger cross sectional area because they have much thicker insulation for direct burial application.

If not using compact conductors and you used a SCH80 sweep (as compared to a sch 40 sweep) then you will have to reduce the neutral from 2/O to 1/O in order to meet the 2" conduit fill limit.

The wire that I was referring to previously is a type made by Southwire called Simpull Aluminum THHN. It is stocked at my local electrical distributors, and dual rated THWN-2, and is a "compact" wire. In my shop build I had a similar situation as you and ended up using larger sized wire to account for voltage drop so your situation was nearly identical to mine with only a bit longer run.
Brian

 

[ard]

Sorry, yes there is a disconnect. Also, I may have messed up in that I poured 2 2" PVC sweeps into the corner of my slab for the feeder. If I have to have larger than 250MCM, can I put say two conductors in each 2" conduit or do they have a sheathing around them?

Code question for the experts:

Can he run say 3" 500 feet to a flush, in ground concrete pull box, placed 25 feet from the garage- then SPLIT the 4 wires and feed 2 wires into TWO runs of 2" PVC that then run up into the panel???

 

[Aceman]

I agree with bjcouche's wire sizes.

For reference, our crew pulls in feeders this long and longer on a regular basis so you can take this for what it's worth.

I would abandon the 2" you've got and install one 3" pvc conduit with 36" radius fiberglass sweeps at the ends. With 525' of pull you need to be thinking about burn through at the 90's with whatever you're using to pull it with. If you want to save a little money, you can use a 36" pvc sweep at the feeding end.

I would also install a 200 amp panel in the shop, it will be able to handle the wire sizes you're using without an issue. Plus, they come with more breaker spaces, generally.

 

[mm08822]

Code question for the experts:

Can he run say 3" 500 feet to a flush, in ground concrete pull box, placed 25 feet from the garage- then SPLIT the 4 wires and feed 2 wires into TWO runs of 2" PVC that then run up into the panel???

No, all conductors of the circuit including the egc must be included in both parallel conduits.

Either abandon those 2" sweeps for this purpose or reduce (really confirm) the load to be served. OP really needs to evaluate if he will ever be pulling close to 100a.

Another option is to determine max fill for 2" and where that puts him service wise. If acceptable ampacity, then use your pullbox idea to transition from the 3" to the 2" for the last 10-20'. You could even splice into smaller size conductors at this close location, but I would suggest having zero underground/moist splice locations whenever possible.

 

[rjprice]

Thanks, to all. I'm a mile wide and an inch deep when it comes to electrical.

I should have put a larger (metal) sweep in the slab for sure. At the meter, I have 2 200A panels (one for the house and one for the barn). I have yet to do the trench. I will have to rent a rock saw as it is solid rock here in S. Texas. The sparky mentioned using a metal sweep out of the meter rack due to the plastic getting cut by the pull cord. He also mentioned putting in a "pull box" midway.

So if I understand correctly then if I start with 240 (246 as measured) volts at disconnect and have 3.7% drop, then I would still have ~231v at the barn at 100A? Am I looking at this right?

As for the wire, I could always come into the building from the outside and not use the sweeps in the slab. Then I could use a larger (350MCM?) wire & conduit if i did this. Sounds like the 250MCM wire would work fine, though.

as for load, here is the lighting: I plan on 12 165w James LED high bays, 6 48w wall packs and 6 48" vapor tight 48w on the 15x50ft lean-to.

Thanks again for your help.

 

[bjcouche]

It sounds like your sparky knows what he is doing. He was planning to use 250MCM, was planning on installing a metal sweep at the meter / disconnect and pull from that location.
Aceman has good practical advice from experience. A 36" sweep is a larger radius than normal which makes the pull easier due to not bending the wires so sharply. It also helps with "burn through" which is the action of the pull rope rubbing on the inside wall of the conduit, sort of like a chain saw affect.. One disadvantage of the 36" sweeps, is that you have to bury them 36" deep because they take 36" in height to turn 90 degrees. I would never bury metal conduit due to rusting, but I was also not aware that they made fiberglass conduit, sweeps, etc, specifically to address this issue. Looks like these products are used more often in industrial and commercial applications.
If it's an option for your sparky I would use the fiberglass sweep on the pull end instead of the metal sweep.
I would not put any splices underground if at all possible.
My previous posts were to show you that you COULD use your existing 2" conduit if you really wanted to go through the effort. You could also just come up out of the ground outside of the garage and then go through the garage wall above grade with an LB. Then you could use 2.5 or 3" PVC for the entire run (with the fiberglass sweep on the pull end).
Based on your electrical needs, I don't see you needing to go larger than 250MCM. If you go larger than 250MCM, then you'll have to reduce down to 250 or smaller because 250 is the largest that will fit in a 200A panel IIRC.
If you don't use the 2" conduit, your electrician will likely pull a neutral and ground that is larger than I suggested and that's fine.
Brian

 

[rjprice]

Brian, thanks again. I will pass along your suggestions. They make a lot of sense.

 

[wyliesdiesels]

The details: 40x60 barn. I Want 100A panel, 525ft from newly installed meter rack. What size aluminum feeder and how many conductors and will it fit in a 2" conduit?

also, if I have a ufer ground at the barn do I need to run a ground from the meter rack?

My sparky says 250mcm will work with just under 5% voltage drop.

According to the calcs I did, with 250mcm, 100a and 525' you will have 9.87v drop or 4.1%. NEC recommends 3% for feeders and 5% for branch circuits.

However, I doubt you will be using 100a very often. But If you wanted to stay @ 3% or under you need to use 400Kcmil AL....

 

[bjcouche]

Wyliesdiesels, when you came up with 4.1% voltage drop, at 525ft of 250MCM at 100A, 240V, What resistance per foot were you using? I used 0.0845ohms per 1,000 feet. and came up with (((0.0847/1000)*(525*2))*100)/240 = 3.7%
I got 0.0847 from NEC chap 9 table 8, DC resistance. Table 9 is for 3 phase... Looks like we both agree that he should use use the 250MCM and it will be fine for his needs, just wanted to clarify the difference in calculation.
Brian

 

[mm08822]

Wyliesdiesels, when you came up with 4.1% voltage drop, at 525ft of 250MCM at 100A, 240V, What resistance per foot were you using? I used 0.0845ohms per 1,000 feet. and came up with (((0.0847/1000)*(525*2))*100)/240 = 3.7%
I got 0.0847 from NEC chap 9 table 8, DC resistance. Table 9 is for 3 phase... Looks like we both agree that he should use use the 250MCM and it will be fine for his needs, just wanted to clarify the difference in calculation.
Brian

Table 9 is better to use even on single phase AC loads as there is some consideration for power factor built in to it. This is a little more conservative for Voltage Drop. Purely resistive AC loads could use table 8 or 9 as the resistance values are virtually the same b/c the inductive reactance component is 0. Once you add a bunch of motors to the load, the inductive reactance component increases.