sub-panel in barn...again

[mathey]

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]

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]

</font><font color="blue" class="small">( 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. )</font>

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]

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]

tc35dforme,
<font color="blue"> 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. </font>

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

 

[SPIKER]

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]

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]

No Spiker, you do NOT have to run 4 wires

Copied with permission from the 2005 NEC® website:

<font color="blue"> (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
</font>

 

[Inspector507]

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

 

[mathey]

</font><font color="blue" class="small">( Is your water line going to the barn going to be metal )</font>

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