sub-panel in barn...again

mathey · Feb 23, 2005

After reading just about every post relating to this, here's where I am...

I'm in the planning stage of running electric to a barn behind my house. The distance from panel to panel will be about 150 feet max. I will bury 2 inch conduit approximately 24" in the ground and pull either a single #8-3 w/grnd copper wire or four seperate #8 THHN copper wires from panel to panel (2 hot, 1 neutral, 1 ground). I will have a 40 amp breaker in the main panel and two 20 amp breakers in the subpanel. The barn will only have lighting and outlets (total right now 14), nothing major. Since there will be metal to metal between the buildings (phone, intercom) I will ground to the main panel and not install a ground rod at the barn.

my questions are:

1. does everything mentioned look ok?

2. will the 2 20 amp breakers at the sub panel be standard 120v? (i don't think I'm understanding the 240/120 thing completely)

3. anything I've missed or overlooked?

thanks!

Mark

tc35dforme · Feb 23, 2005

I'm weird, but I'd run a second empty conduit while I was at it. I'd even price 3" as opposed to 2". You never know what may be required in the future. It's easier to pull through a larger conduit. Not sure what the cost increase would be. Be careful with backfill, watch rocks..they are conduit killers. Mark the conduit with a buried plastic warning tape about 12" above the conduit to warn any future diggers.

As for the 240/120 thing, a standard house panel has either 3 or 4 feed wires. One is 'Hot' ( Line 1 ), one is 'Hot' ( Line 2 ), the others are neutral and/or ground ( Neutral Grd ). Line 1 to Line 2 gives you 240 volts. Line 1 or Line 2 to Neutral / Grd gives you 120.

Based on what I'm reading, sounds like you want to put ( 2 ) single pole breakers in your main and run a pair of feeds to the barn and skip the breakers in the barn. Maybe not what I'd do.

Why not just run a 60 amp 240 volt feeder to a real sub-panel in the barn and then go from there. I'd also ground at the barn. The extra ground rod will do no harm.

DocHeb · Feb 23, 2005

( real sub-panel in the barn and then go from there. I'd also ground at the barn. The extra ground rod will do no harm. )

But it will be against code (at least to my understanding - maybe Inspector 507 will chime in here.) Subpanels should not have a separate ground - they should use the main panel's ground. I agree that he should put a real sub-panel in the barn, and the 60A -240v would be about right. This would cover everything from lighting to a welder in the future. I'd hate to put the time into the project, only to be short on juice later.

For 150 feet at 20A, #6 wire copper (or #4 aluminum) will be required. For the proposed 60A sub panel, the wire should be #2 copper (or 2/0 aluminum). See Voltage drop calculator

I agree with the 3" conduit - the price difference between 2" and 3" is negligible. Consider running wires so a three way switch can control an outdoor light from both the barn and the house.

Inspector507 · Feb 23, 2005

Mark,
Sounds like it's okay to me, but that is a long distance for #8 and a 40A breaker. Although you may be ok as all the lights and outlets MAY not be in use at the same time. If you run 4 wires out to the barn a grounding electrode is NOT required. If you run 3 wires out, it IS required.

Inspector507 · Feb 23, 2005

tc35dforme,
 Based on what I'm reading, sounds like you want to put ( 2 ) single pole breakers in your main and run a pair of feeds to the barn and skip the breakers in the barn. Maybe not what I'd do. 

Re-read his post, he wants to put a 40A in the main panel and use 2 20A's in the barn

SPIKER · Feb 23, 2005

actually code states that if you are making a sub panel in a out building then you HAVE to run 4 wires, (2 hot legs one Netrual leg and one ground wire) then you HAVE to sepperate the Ground bus and the NETRUAL buss inside the new sub panel and install a ground rod at the new location to ground the new sub to. (this is per the 2002 NEC it is setting here but I don't know the sections right of top of head and don't feel like searching for it) note this is IF you are running a 2nd sub panel! individual circuits of 120 volts for lighting does not have to do this.

many people read the code differently the above is how I interpet it. I think inspector can chime in too. the ampearge is ok for the stated load but that is rarely the case XX months later when someone sticks a bigger breaker in the house panel and over loads the underground wires or plugs in a welder or compressor into the shop...

anyhow hope this helps.
MarkM

looks like inspector was typing same time as I was...

mathey · Feb 23, 2005

Seems I left out a few details...i will have a single trench 36-42" deep...2" conduit at the bottom that will house 3/4 inch water line...then backfill to the 24" line and a 2" conduit for the electric (must be 4 individual wires if in conduit) and a seperate #12 return wire for a remote switch back at the house. Then more backfill and another 2" conduit for low voltage (phone, intercom).

I definitely will have breakers at both ends and a small panel in the barn. I have layed out 14 drops (10 lights and 4 outlets). Rule of thumb is 10 drops per 20 amp breaker, so that leaves me with 6 to spare. plan is to have two 20 amp breakers in main panel and two 20 amp breakers in the barn. Keep in mind the "barn" is only 24x24 and primarily for storage and it has one horse stall, just need some lights for working after dark. I have a "real" garage as well, and alot of the gardening stuff will be moved from the garage to the barn.

As for the ground, aparently i will need a ground rod at the barn end as well as a ground back to the main panel.

As for wire size, correct me if i'm wrong, but a 4 wire system uses the 240 volt portion of the chart? Voltage Drop Calculator Oh, it looks like the calc you used allows for 3% and the other 5%.

here's a picture similar to what i'm planning:

Inspector507 · Feb 23, 2005

No Spiker, you do NOT have to run 4 wires

Copied with permission from the 2005 NEC® website:

 (2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of either of the following:

(1) That required by 220.61

(2) That required by 250.122

Inspector507 · Feb 23, 2005

Mark,
Is your water line going to the barn going to be metal?? That changes everything here.

mathey · Feb 23, 2005

( Is your water line going to the barn going to be metal )

nope, poly! and apparently low voltage wires don't count either

Inspector507 · Feb 23, 2005

Then you do not have to run 4 wires unless you want to. If you run 4, no grounding electrode is needed.

edit.......
At least according to the 2002 and 2005 NEC®. Your local codes may vary.

_RaT_ · Feb 23, 2005

As the Inspector says, "your code may vary". Ours would require 4 wires. The ground at the barn may set up a situation of disimilar grounding potential and thereby actually develop a voltage to ground between the 2 grounds. Thats providing I understand it correctly, it gets complicated. Running 4 wires is safe. A 2" conduit is overkill.

fractal · Feb 23, 2005

The only thing I will add to the discussion is .. labor around here is expensive. It would be most unfortunate if you found yourself digging that ditch in a year or two because you did not provide enough power. I would consider a 50 amp circuit the minimum I would run to a full fledged shop/barn. That will let you run a basic 220 buzz box welder. I do not have the charts in front of me but I believe #6 is good for 50 amps at 150 ft.

You said you were going to put a 40 amp 220v breaker in. Your wire is a little light for 40 amps but it looks like you are only planning on deploying 20 amps of it assuming you put each of the 20 amp breakers in your barn on different legs which would be the smart thing to do.

Might I suggest you price check wire at your local electrical store and decide where the price starts to hurt. It does not cost THAT much more to run a size or two bigger than you think you need today to make sure you have capacity for tomorrow.

I know I sure would not put 14 shop outlets on a single 20 amp circuit, and I hope you realize that you are not supposed to have lighting on the same circuit as tools ... oops, just turned on the shop vac and blew the breaker taking out the lights right after starting up the saw so there is this sharp piece of metal spinning inches from my fingers and it is dark...

As for ground rods. The code on what you are required to do changes often. If it were me, I would run 4 wires AND I would drive a local ground rod. This is not (currently) required by code but it is not prohibited.

EddieWalker · Feb 23, 2005

Running water and power in the same trench may or may not be legal in your area. Lots of places it isn't allowed.

I would run it in a seperate trench. If the water line ever breaks, then you will have to dig it up and work around the power lines.

Turning off the power will protect you, but there's no gurantee you won't damage the power lines when digging up the water line.

I know some peopel who put them on the oposite edge of a two foot wide trench. That might work better, but still not ideal.

Mark you water line with a copper wire also. It's real easy to forget the exact location ten years from now.

mathey · Feb 24, 2005

I appreciate all the responses!

I've spoken to lots of different people with many diverse backgrounds and have gotten info that has been all over the map.

I will go to the county electrical inspector and he will have the final say on my plans...since he's the one that's gotta sign on the dotted line anyways.

It appears that electrical wiring is alot like Geometric Dimensioning and Tolerancing...its subject to interpretation!

Thanks again for your time and insight!

Junkman · Feb 24, 2005

( .....................It appears that electrical wiring is alot like Geometric Dimensioning and Tolerancing...its subject to interpretation! )

Add hydraulics to that list also..... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

srs · Feb 24, 2005

( Running water and power in the same trench may or may not be legal in your area. )

Eddie, I too do not know if running water and power in the same trench is legal, but he will run a 3/4" water line inside a 2" PVC pipe. So I guess his thinking is if the water line should ever break he could just pull the 3/4" line out from either end. I personally would dig a separate trench just to be on the safe side.

SPIKER · Feb 24, 2005

( No Spiker, you do NOT have to run 4 wires

Copied with permission from the 2005 NEC® website:

 (2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of either of the following:

(1) That required by 220.61

(2) That required by 250.122
 )

this is true but you missed the part where in section 250.32 A it states that if "where there are no existing grounding electrodes, the grounding electrod(s) required in partIII of this artical shall be installed." there is an exception but that only pertains to a single branch circuit. and he wants 220.

part III is on page 70-104 (in nec2002) states what type of ground rods and or piping is useable.

section 408.20 states that " grounding of panel boards panelboard cabinets and panelboard frames, if of metal, shall be in physcal contact with each other. and shall be grounded. ..." but that is slightly off topic: still I can't find the section where the netural & gound in second panel should be disconnected. the above was fast and simple to locate. and the new 2005 may not have it in there anymore.

still it is wise to defer to the local inspector /forums/images/graemlins/wink.gif even if he is # 57 /forums/images/graemlins/laugh.gif

Inspector507 · Feb 25, 2005

Spiker, after re-reading my posts, I did make a mistake when saying that a grounding electrode is not required, it would be. But you still do not have to run 4 wires /forums/images/graemlins/grin.gif