Wiring a pole building - Is this crazy?

[carhunter]

Well, this building has kind of morphed itself into existence. I recently moved into a new home on 5 acres. 2-1/2 ac of it is lightly wooded, slightly below grade, and beautiful. We decided to put up a pole building out of sight so as not to detract from the property/view, and ended up with a 40x54x14 planned out. (It would have been a little bigger, but township zoning was 'difficult' to work with at best)
So I thought I'd get started on a foundation and stop until spring 2011. Everything turned out to be more difficult than we first thought...Long story short, I worked hard and made some extra money this year, contractor really wanted the work, I landed some good prices on materials, and lo and behold there's a building in my backyard.

Er...almost, winter has slowed down the trim and final excavating. I'd like to do a build thread when this is all finished but right now I've got an electrical question.

Due to necessity, the building is just a tad over 600' from the house, which has 200 amp service. We've discussed options with the local utility, and by far the cheapest route is to install a larger meter and go directly to a main disconnect then out to the building underground. Anything else is $5-6k more expensive.

I thought it would be out of the question at all given the distance, and had actually planned on solar or a generator for basic lighting (building would be mainly for storage), but looks like its possible.

Have been doing a lot of reading, maybe to my detriment, but its given me questions...

Here's the particulars -

add 320 amp 'extended range' meter base
4/0 al from the meter to 200 amp disconnect, then out to the building via trench.
Into the building with service to a 200 amp panel.

I'd like to clarify what everyone is telling me...Inspector says he'll ok whatever utility co says.

What type of cable is appropriate? Utility co says 4/0 4/0 2/0 direct burial USE-2 and add an extra 4/0 to make it 4 wire, then ground rods at the building. (there's no plumbing or metallic paths connecting the house and building).

Service entrance cable - this means its ok to enter a building to connect to the panel and meter? Meter is about 25' away from where cable will enter garage. (garage is an addition, and meter is attached to former exterior wall of house with an elbow to allow the meter to be read through the window).

Footer - there is a footer and retaining wall along one side of building. However there is no provision for ufer ground. Inspector so far hasn't mentioned anything, but is this enough to require it in addition to ground rods? Concrete floor may be added later, but not now.

Anyone want to tackle this?! My head is spinning already. Thanks!

 

[ishiboo]

Well, this building has kind of morphed itself into existence. I recently moved into a new home on 5 acres. 2-1/2 ac of it is lightly wooded, slightly below grade, and beautiful. We decided to put up a pole building out of sight so as not to detract from the property/view, and ended up with a 40x54x14 planned out. (It would have been a little bigger, but township zoning was 'difficult' to work with at best)
So I thought I'd get started on a foundation and stop until spring 2011. Everything turned out to be more difficult than we first thought...Long story short, I worked hard and made some extra money this year, contractor really wanted the work, I landed some good prices on materials, and lo and behold there's a building in my backyard.

Er...almost, winter has slowed down the trim and final excavating. I'd like to do a build thread when this is all finished but right now I've got an electrical question.

Due to necessity, the building is just a tad over 600' from the house, which has 200 amp service. We've discussed options with the local utility, and by far the cheapest route is to install a larger meter and go directly to a main disconnect then out to the building underground. Anything else is $5-6k more expensive.

I thought it would be out of the question at all given the distance, and had actually planned on solar or a generator for basic lighting (building would be mainly for storage), but looks like its possible.

Have been doing a lot of reading, maybe to my detriment, but its given me questions...

Here's the particulars -

add 320 amp 'extended range' meter base
4/0 al from the meter to 200 amp disconnect, then out to the building via trench.
Into the building with service to a 200 amp panel.

I'd like to clarify what everyone is telling me...Inspector says he'll ok whatever utility co says.

What type of cable is appropriate? Utility co says 4/0 4/0 2/0 direct burial USE-2 and add an extra 4/0 to make it 4 wire, then ground rods at the building. (there's no plumbing or metallic paths connecting the house and building).

Service entrance cable - this means its ok to enter a building to connect to the panel and meter? Meter is about 25' away from where cable will enter garage. (garage is an addition, and meter is attached to former exterior wall of house with an elbow to allow the meter to be read through the window).

Footer - there is a footer and retaining wall along one side of building. However there is no provision for ufer ground. Inspector so far hasn't mentioned anything, but is this enough to require it in addition to ground rods? Concrete floor may be added later, but not now.

Anyone want to tackle this?! My head is spinning already. Thanks!

I would look for 4/0 4/0 4/0, since I do not believe the 2/0 ground is required. The code gurus can answer that. PVC conduit from the entrance to the panel in the garage.

It will be cheaper to rent a trencher and buy the wire than just the initial purchase on the generator, let alone fueling it and maintenance.

 

[mrb]

where are you and what code cycle are you on?

 

[Norcal]

Be aware that 4/0 AL to your pole barn is not suitable for 200A,it does not meet the criteria allowing undersizing your wiring.

 

[carhunter]

thanks for replying. We're in southern ohio, I believe we're on nec '08.

I thought 4/0 al was rated at 205 amps? I'm not overly concerned about getting max amperage at the panel, so should I match a breaker to the wire, and what amperage would I be seeing at the building?

 

[mrb]

you need to calculate your load to see what kind of voltage drop youre going to see. At 600ft 4/0 is good for 70 amps of load to stay at 3% vd.

4/0 AL is rated at 185 amps. You cant use the 90 deg column (this is where 205 amps comes from) for breaker sizing.

You will have to run 4 conductors to the building (and install grounding electrodes). You cant install a 3 conductor cable and add an additional wire. All circuit conductors must be in the same cable or conduit.

 

[carhunter]

you need to calculate your load to see what kind of voltage drop youre going to see. At 600ft 4/0 is good for 70 amps of load to stay at 3% vd.

4/0 AL is rated at 185 amps. You cant use the 90 deg column (this is where 205 amps comes from) for breaker sizing.

You will have to run 4 conductors to the building (and install grounding electrodes). You cant install a 3 conductor cable and add an additional wire. All circuit conductors must be in the same cable or conduit.

That's very interesting. The utility company ran their numbers and said we'd be good for 130 amps with 4/0, the electric supply place said 70 amps. When we asked utility co why the difference, he said the other guy had his calcs backwards, which I tended to believe becase it was good news So do we size the breaker to 70 amps?

Was also told to use 4/0-4/0 2/0 off the spool, which is 3 separate conductors, then use another 4/0. All of this will be trenched 24" deep w/o conduit, except where it crosses the driveway. That will be in 2" gray conduit.

Is 3% vd the rule, or what is an acceptable range to work in?
Thanks! Great info.

 

[carhunter]

I'm also assuming we need a main disconnect sized at 70 amps?

 

[mrb]

there is no code requirement to compensate for voltage drop -its a design issue. That said you do need to consider it, i dont think you want 90 volts at your building.

Why would you buy three conductor cable and one extra wire? Why not just buy four conductor cable?

You need to do the calculation to find the proper EGC size when increasing conductor size for voltage drop. 2/0 may or may not be ok.

 

[Charles (in GA)]

If you ever plan on using this building for anything other than "storage" you certainly need to consider getting enough power to the building for you or the next guy (it will help resale.... no, no one ever plans on selling and moving, but it happens).

Even if you have to spend more money, did the power company give you a figure for taking the high voltage line to the building, either overhead or underground, with the transformer next to the building, then you could have a 200 amp meter, and full 200 amps of service to the building for that lathe, mill, air compressor and zillion watts of fluorescent lighting you don't intend on installing.

I don't know if a Ufer ground in the slab only is OK or not, but if it is, you need to plan on it when you do the slab, and in the meantime, use two ground rods.

Charles

 

[carhunter]

Hi Charles,
I agree but 200 amp seems overkill for the price I'd pay. Utility co quoted about 7500 just for the poles and installation, not to mention a lot of tree work that would have to be done along the drive. (tree lined all the way back, zoning won't let us move the drive without a complete repermit).

I could possibly upgrade wire, but it might net me what, maybe 20 more amps? I'm limited to 200 amps at the meter and a tap off the transformer is the only other option?

But its a valid point, in our area it would help resale if someone could come in and run a small commercial shop back there. It would have more power than most houses around here!

Bonus - This evening I discussed moving the meter out of the garage with the contractor and it looks do-able. It will make for a cleaner install, and I never liked the meter on the wall anyway. The way its configured is always in the way, the window for the meter reader to see it is a security risk, etc...Also the new disconnect panel that comes off the meter to feed the building will have several breaker slots, so if the wife decides on any landscape lighting, etc, it will be ready to go!

Cross your fingers!

 

[carhunter]

Why would you buy three conductor cable and one extra wire? Why not just buy four conductor cable?

You need to do the calculation to find the proper EGC size when increasing conductor size for voltage drop. 2/0 may or may not be ok.

Don't have a ready answer for that except that's the way its available from the supplier. For some reason 4/0-4/0-2/0 is commonly available for direct burial, even though its only 3 conductor. Its not sheathed together like you may be thinking, it just comes as three separate wires.

 

[mrb]

Don't have a ready answer for that except that's the way its available from the supplier. For some reason 4/0-4/0-2/0 is commonly available for direct burial, even though its only 3 conductor. Its not sheathed together like you may be thinking, it just comes as three separate wires.

i know what it is. i would just order the right cable instead of cobbling something together. Also make sure its dual listed and not only USE so you can run it in the building.

did you calculate the required ground size based on the proprotional increase in conductor size when youre using 4/0 AL upsized for vd on a 70a circuit?

 

[carhunter]

i know what it is. i would just order the right cable instead of cobbling something together. Also make sure its dual listed and not only USE so you can run it in the building.

did you calculate the required ground size based on the proprotional increase in conductor size when youre using 4/0 AL upsized for vd on a 70a circuit?

That's what I've been asking, what is the right type of cable? I haven't done calc's, just going off what inspector/utility co are telling me. I understand the basics but am not an engineer/electrician/builder.

I've learned to check everyone's work, regardless of the job. Never hurts.

I don't understand the dual listed part. If its rated 'service entrance,' is it ok do go into the panel inside the building (through conduit of course)?

 

[Aceman]

Be aware that 4/0 AL to your pole barn is not suitable for 200A,it does not meet the criteria allowing undersizing your wiring.

The only criteria it has to meet is 240.4(B). Since his load is most likely under 180 amps, it's legal.

you need to calculate your load to see what kind of voltage drop youre going to see. At 600ft 4/0 is good for 70 amps of load to stay at 3% vd.

I calc'ed it at 59 amps. 70 amps if I used 250kcmil.

did you calculate the required ground size based on the proprotional increase in conductor size when youre using 4/0 AL upsized for vd on a 70a circuit?

It doesn't make sense to spend money on insulated taps/split bolts/j-box/etc to splice a smaller conductor wire onto that 4/0 just so it'll fit a tiny 70 amp breaker, in addition to having to upsize the ground wire for voltage drop reasons. I'd probably buy just a 250kcmil mobile home feeder cable(4 wire) and land it right onto that 200 amp breakered disconnect with no worries about upsizing the ground wire for voltage drop.

But, I think all of this is missing the point. You don't waste money guessing wire sizes on a 600' run when you don't know the load.....it's silly.

He needs to figure out his equipment and HVAC load and then pick the wire size!

 

[carhunter]

Well, I try to keep tools, etc pretty simple. I'm planning:

3 or 4 runs of hi efficiency t8 flourescents rated at .68 amps/ballast. (I want to keep all lights on a single circuit, or split into two 10 amp circuits for front and rear halves of building)

max draw would be occasional use of a lincoln 225 arc welder (35 amps? )
compressor - 15 amp max
mig welder - 15-20 amp max
the usual hand tools, etc for car restoration and maintenance running one at a time. Same for the welder and compressor, I never run one while the other's on. Force of habit.
Heat - maybe a waste oil furnace or propane rig, something very simple. AC maybe in an office area, but it would only be a 110v plug in type.

Not planning an all out, 24-7 commercial workship. Heck, it won't even have concrete for the first year, and even then it depends on how much work I'm turning out there.
Ideally, it would be a nice place to fall back on if my job situation changes. Work from home you know, but I also want to keep power consumption and cost of operation to a minumum.

But yeah, I can see how we might need to upgrade the wire spec. Will 250 kcmil fit a 200 panel?

 

[Charles (in GA)]

Well, I try to keep tools, etc pretty simple. I'm planning:

3 or 4 runs of hi efficiency t8 flourescents rated at .68 amps/ballast. (I want to keep all lights on a single circuit, or split into two 10 amp circuits for front and rear halves of building)

max draw would be occasional use of a lincoln 225 arc welder (35 amps? )
compressor - 15 amp max
mig welder - 15-20 amp max
the usual hand tools, etc for car restoration and maintenance running one at a time. Same for the welder and compressor, I never run one while the other's on. Force of habit.
Heat - maybe a waste oil furnace or propane rig, something very simple. AC maybe in an office area, but it would only be a 110v plug in type.

Not planning an all out, 24-7 commercial workship. Heck, it won't even have concrete for the first year, and even then it depends on how much work I'm turning out there.
Ideally, it would be a nice place to fall back on if my job situation changes. Work from home you know, but I also want to keep power consumption and cost of operation to a minumum.

But yeah, I can see how we might need to upgrade the wire spec. Will 250 kcmil fit a 200 panel?

You won't run them both till you get that plasma cutter

Actually you are describing quite a bit of consumption. The A/C for example is not much but will tie up a 120v circuit, and the waste oil heater will need a dedicated 20 amp circuit and draw close to 16amps (you are running ignition, fuel pump, and blower) and you must have the air compressor available and it will be running also, or you have to have a small dedicated compressor, thats another 20 amp circuit.

Need to get that transformer closer somehow.

Charles

 

[Norcal]

................................................................................................................................

But yeah, I can see how we might need to upgrade the wire spec. Will 250 kcmil fit a 200 panel?

It should, but check before buying.

 

[banzaitoyota]

AAACK, You have my sympathy.
My Electric Co-Op dropped another 200 amp service (underground) for a whooping $140 when I started my build

 

[rodm1]

What about just going 100amp? 600ft is a long ways and I doubt you will need over 100amps.

 

[mrb]

What about just going 100amp? 600ft is a long ways and I doubt you will need over 100amps.

the 250MCM wire we're talking about is only going to get him around 70 amps usable....

 

[carhunter]

I may have to adjust my priorities, remember this started out with storage in mind and grew into a workshop. So that takes me back to lighting, 5 hp compressor, ability to run a several types of welders. Heat and AC are convenience items andcan be switched off if necessary I guess.
10 amps lighting
10 amps additional lighting
40 amp breaker for 240v tools (will rarely be maxed unless the old Lincoln welder is in play. If I was to add a tig welder, it would be a Miller inverter unit which require less power than the old units)
20 amp for hand tools (including small 110v plasma cutter, as someone mentioned)
So that's 80 amps, but will I be pulling any more than 50 at any one time? Tough call.

 

[carhunter]

AAACK, You have my sympathy.
My Electric Co-Op dropped another 200 amp service (underground) for a whooping $140 when I started my build

I'm jealous! They may have done something similar for me if it wasn't for the distance. Utility will only bury 250ft of cable, anything longer is pole mounted.

Unfortunately we're compromising a lot, but the end result will be a dream come true!

 

[bjcouche]

I'll post some suggestions here that I ran into while having the same problem with my building distance to my meter. The NEC recommends (key word recommends) a 3% max voltage drop on feeders and a 5% overall drop. I would learn how to do the voltage drop calculations yourself and start playing with some numbers.
The first thing to look at is the cable resistance changes with temperature. the hotter it gets, the higher the resistance. Since you are oversizing your cable to lower voltage drop, the temperature rise of the wire is greatly reduced, not to mention you are direct burying it. You are drawing under 100A on a cable normally rated just under 200A (4/O al). I would use the cable resistance at a temperature of not more than room temp. The in ground temp should be even lower. For example, 4/O aluminum has a 20C resistance of 0.082ohms per 1000ft but at 75C it's 0.100.
The next thing to try is to look at the big picture. Maybe if you oversize some of your branch circuits in the building for those longer or higher current runs, you can reduce their voltage drop to 1%, giving you 4% to work with on your feeder. Also, sometimes it is just a matter of placement of your equipment. Can you place all of your high current devices near the load center in the building thus reducing the branch circuit length and drop? In my building, changing the location of the load center from one corner, to the center of a long back wall made a significant change in overall voltage drop, not to mention cost of wire.

Here's my calculation:
3% voltage drop is 240V*.03= 7.2V
cable resistance at 20C is (600ft *2) * (0.082/1000) = .0984ohms
cable ampacity at 3% drop = 7.2V / .0984ohms = 73.2A
Doing the calculation over at 75C gives 60A

If it were me I'd call it 75A useable service. Maybe this can be bumped up a little by lowering some branch drops too. I would probably size the feeder breaker somewhere between 80-100A. Maybe even 125A if I had a lower rated breaker in a disconnect or main breaker panel in the building. That way if you trip a feeder breaker it will be in your building not your house 600ft away. Remember, breaker sizing is for wire protection, not voltage drop protection.
I've found out that the largest conductor to fit in a 100-125A load center is 2/O so you'll have to drop down in wire size at your panel or use a 200A subpanel even with a 75A feed.
Another thing, when you are adding up your loads, balance the 120V loads out. For example, two 10A 120V lighting loads = 1 10A 240V load.
1 10A lighting load (2 120V lighting loads)
1 30A air compressor (I gave you a big one)
1 30A welder
1 15A 120V air conditioner plus extra 15A load

Total is still only 85A even for the very brief time the compressor and welder are running simultaneously.

 

[carhunter]

That's a very rational response, thanks. My goal with this was not max power, but a reasonable amount of power for a limited use structure as you suggest. Granted someone may come along after me and want more juice, but they can spend the 8k or whatever to set poles from the transformer.

I do question downsizing the breaker - I don't think its ok code-wise to go to a smaller cable (via jbox or whatever) and use the 125a breaker at the building panel.

On a positive note, AHJ did a walk through and gave us a verbal ok on the new meter, main disconnect, cable, etc. We don't have ground rods in, or the final part of the trenching finished due to weather, but its getting closer.

 

[bjcouche]

By "under sizing" the breaker, I meant sizing the breaker for less current than the 4/O is rated for but not less than the smallest conductor in the feeder. For example, you can't get 4/O to fit in the lugs of your 100A subpanel. What you could do is provide a junction box before the subpanel and drop down to 2awg aluminum. You would then be limited to a feeder breaker of 90A to protect the 2awg section. If you are connecting directly to a meter and the power company considers your 600ft run a 100A "Service Feeder" then you can use a 100A breaker in your subpanel to protect the 2awg cable. NEC allows you to over rate service feeder wire a little bit. I suggested 2awg aluminum because It's the next common size smaller aluminum, will fit in a 100A subpanel terminal and I don't like mixing aluminum and copper if I can help it.
I'm designing something similar for myself. I want 100A useable about 150ft away. I'm tapping off my main panel with a 100A feeder breaker at 1awg copper, junction box up to 4/O, then at the garage junction back down to 1awg to terminate at the subpanel. I could go all 1awg copper but it's cost prohibitive.

Brian

 

[carhunter]

I see now, that makes sense.

As you suggested, we've got everything close to the main panel. There will be a work area at the front of the building, so all the outlets including 220v will be within 10-20 ft of the panel. The welder has a huge ext cable if necessary. Only other power will be lighting (hi efficiency, limited to 2-10 amp breakers for front and rear areas) and a couple convenience outlets in the back, maybe. If I add heat and air, I'll subdivide and insulate the front portion for efficiency, the rear is 'cold storage'

I don't want a huge electric bill either!