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neonhomer
KK4BFN
Premium
join:2004-01-27
Edgewater, FL

How deep to bury a 110vac line

Okay... I am tried of the extension cord that has been running across my back yard for about 10 years that powers my shed. The shed just has a duplex outlet and a single light. It is wired with 14ga I think.

Well, I am tired of it, and I am going to run proper power to it. That I want to put a 30A 115v outlet out there for my camper. A friend of mine who I worked with down in Ft. Pierce gave me the wire (three 200' spools of 10ga) for the job, but I have to put it in conduit. No big deal. 3/4" pvc conduit is only $2 / 10' section. It's about 120' total run from the shed to the breaker box (it's located on the outside of the house.).

Here is the question. How deep does the conduit need to be? I was thinking 2-3', my dad thinks 18" is enough (he's the one digging the trench!). I tried browsing through the 2008 NEC but couldn't find it.

How deep do I have to be? If it matters, I am on the east coast of Florida, about 5 miles inland, and about 1 mile from the river.
--
"I reject your reality and subsitute my own!" - Adam Savage, Mythbusters
"We're either gonna die or gonna fly...", Jamie Hyneman, Mythbusters

The odds of me voting Republican are about as good as LHC creating a black hole big enough to swallow the Earth!



mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3

This topic has been answered before by whizkid3 See Profile. Here is the link to the thread --> »Re: get power to garage

18" is the code requirement, with the exception whizkid3 notes in his post. I am sure he can answer more questions if you have them.



steve1515
Premium
join:2000-08-07
Peabody, MA
reply to neonhomer

Since you want multiple circuits, you're going to need to install a sub-panel w/ ground rod in the shed.



neonhomer
KK4BFN
Premium
join:2004-01-27
Edgewater, FL
reply to mattmag

Now why did I not get then when I searched? Oi vey....



Splitpair
Premium
join:2000-07-29
Cow Towne
kudos:3

1 edit
reply to neonhomer

said by neonhomer:

How deep do I have to be? If it matters, I am on the east coast of Florida, about 5 miles inland, and about 1 mile from the river.
NEC 300.5 column 3.

Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.

GdotMikeL

join:2001-04-23
West Chicago, IL
reply to neonhomer

When I ran power to a detached garage the village only required a 12 inch trench- if in conduit. I think they required 24" for direct burial. You should call your local building department for the right answer for your location. And after digging that trench by hand I would highly recommend renting a trencher.



whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9

4 edits
reply to neonhomer

said by neonhomer:

The shed just has a duplex outlet and a single light. That I want to put a 30A 115v outlet out there for my camper. (three 200' spools of 10ga) 3/4" pvc conduit - 120' total run.
The duplex receptacle must be on a separate (15A or 20A) circuit from the 30A camper receptacle.
said by neonhomer:

How deep does the conduit need to be? ...my dad thinks 18" is enough.
Your dad is correct - 18" minimum to the top of the conduit.

said by GdotMikeL:

the village only required a 12 inch trench- if in conduit. I think they required 24" for direct burial.
The rules have changed. Its 18" for PVC conduit (rigid non-metallic conduit). Its 30" for direct burial. Your village may have ammended the code, but the depths you quoted were allowed in older versions of the NEC, I believe. Of course, it can't hurt to check with the local building department. NYC doesn't allow direct burial, period.

said by Splitpair:

NEC 300.5 column 3.
Its column 2, at least in the 2005 NEC (PVC conduit). Then again, the rules and table have changed.

You have a few other problems to worry about, Neonhomer, with multiple solutions. To begin with, if you run the two separate circuits in the same conduit, the ampacity of the wire will need to be de-rated by 80%. So, the 10 AWG wire will be too small for the 30A camper circuit. Assuming your buddy gave you type THWN wire, using the 75 degree C ampacity column, the 10 AWG can handle 35A x 80% = 28 amps. 120 feet is very long for a 12AWG wire to handle a 20A circuit. I am not going to do the voltage drop calculations, but suggest its 28A ampacity would be fine for the 15A duplex receptacle. Try not to go over a load of about 15A at any one time. (Otherwise your voltage will drop below the 3% allowed by the NEC for branch circuits.) The wiring for the camper receptacle after being derated, will need to be 8 gauge minimum. Regarding the fill rate, and assuming THWN wire and schedule 40 PVC conduit, NEC table C.10 allows up to five 8 AWG conductors in the conduit. You need six, but three 8 AWG and three 10 AWG. Again, a complicated calculation that I am not going to do, but would suggest - considering that up to nine 10 AWG conductors are acceptable - that you would be fine. I would use 1" schedule 40 PVC minimum, as I only want to dig the trench once. You will never know when you decide you need another circuit or a sub-panel, etc. (That will bring us to the last solution.)

Another solution, to avoid the de-rating, larger wiring and conduit size issues, would be to simply run one 30A circuit. The camper receptacle and the light fixture can be hung off of this circuit. You can put a 20A fuse block, or fused disconnect switch, in the garage for protection of the duplex receptacle. You can use your 10 AWG wire and 3/4" conduit without a problem.

The last solution (and there are more) is the way I would go. Why bother digging a 120' trench and laying PVC, if you are not going to take full advantage of it? I would go the sub-panel route. Put a little, inexpensive, 240V, 60A 8-pole breaker panel in the garage. Probably run you $50 with the breakers. Put a 60A two-pole breaker in the main panelboard at the house, and run three 6 AWG conductors (two hots and one neutral), and one 10 AWG ground wire from the main panelboard in 3/4" sched-40 PVC conduit. (I would oversize it to 1" PVC make my life easier.) Don't forget the sub-panel needs a separate ground bus and (isolated) neutral bus, and a ground rod at the garage. With that, you'll have almost no end to the circuits you can put out there - perhaps some outdoor lighting or a 240V table saw? You will most likely never have to re-trench again.

Langning
Premium
join:2003-04-28
Marlborough, MA
reply to neonhomer

Whoever put in my yard/drive way post lantern, buried the 15A wire (with no conduit) only 6" deep.



neonhomer
KK4BFN
Premium
join:2004-01-27
Edgewater, FL
reply to neonhomer

Originally, I was just going to wire a 20A circuit for the shed, and that's it. My camper has a 15A plug on it, but I am going to be upgrading that to a 30A (another story) when I add A/C to it.

So, originally, the 10ga wire would have been fine. The reason I am doing this is now I have the wire. I can't afford 400' of 6ga, plus the ground, plus the ground rod, plus the subpanel.... blah blah...

So, as of now, it's just going to be the three 10ga wires. I am going to, however, run 1" PVC and run a pull line as well, so I can go back in at a later date and rewire if I decide I need to.

The wire I am assuming is THWN. I told my friend what I was doing, and this is what he brought me. Going to check though, and if it's not, the whole project just went south...
--
"I reject your reality and subsitute my own!" - Adam Savage, Mythbusters
"We're either gonna die or gonna fly...", Jamie Hyneman, Mythbusters

The odds of me voting Republican are about as good as LHC creating a black hole big enough to swallow the Earth!



whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9

said by neonhomer:

The wire I am assuming is THWN. I told my friend what I was doing, and this is what he brought me. Going to check though, and if it's not, the whole project just went south...
There are other types of wire rated for wet locations, not just THWN. Let us know what type it is.

Since you are just going to run the one circuit, either use the fuse block as suggested above; or keep the breaker in the main panel at 20A.


Splitpair
Premium
join:2000-07-29
Cow Towne
kudos:3
reply to whizkid3

Click for full size
said by whizkid3:

Its column 2, at least in the 2005 NEC (PVC conduit). Then again, the rules and table have changed.
In my 2005 it's 3 for PVC?

Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.


whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9

1 edit

Yeah, mine too. But its the fourth column.

(My aged mind is playing tricks on me.)



steve1515
Premium
join:2000-08-07
Peabody, MA
reply to Splitpair

Splitpair See Profile where did you get that searchable version of the NEC? Looks cool.



steve1515
Premium
join:2000-08-07
Peabody, MA
reply to whizkid3

whizkid3 See Profile I thought that if you have more than one circuit you need a sub panel. Why is this 30A and 20A circuit different?



neonhomer
KK4BFN
Premium
join:2004-01-27
Edgewater, FL
reply to neonhomer

Verdict is in... I am just running the one circuit. I decided to spend the extra money on a better light for inside the shed. Currently it has just a single light bulb. I am going to put up a fluorescent fixture. I am also changing the outlet in the shed to a GFCI.

I looked at the wire, and it says "THHN or THWN", so I am good to go there.

I like that searchable NEC... the only thing I have is a PDF copy of the 2008 NEC.
--
"I reject your reality and subsitute my own!" - Adam Savage, Mythbusters
"We're either gonna die or gonna fly...", Jamie Hyneman, Mythbusters

The odds of me voting Republican are about as good as LHC creating a black hole big enough to swallow the Earth!



Splitpair
Premium
join:2000-07-29
Cow Towne
kudos:3

said by neonhomer:

I like that searchable NEC... the only thing I have is a PDF copy of the 2008 NEC.
»www.nfpa.org/catalog/product.asp···=catalog

Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3



Sheesh..... $100 is a little nuts for something like that. It would make more sense to have it be affordable so more people would buy it and use it.



Splitpair
Premium
join:2000-07-29
Cow Towne
kudos:3

1 edit

said by mattmag:

Sheesh..... $100 is a little nuts for something like that. It would make more sense to have it be affordable so more people would buy it and use it.
Try the 2008 version.

»www.nfpa.org/catalog/product.asp···=catalog

Or e-bay.

»cgi.ebay.com/National-Electrical···0%3A1318

Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3

1 edit

OK, so those are even more nuts... I thought maybe you were going to point me to a deal.



Splitpair
Premium
join:2000-07-29
Cow Towne
kudos:3

It's free here but one has to register.

»www.nfpa.org/catalog/services/Lo···d%3D7008

Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.



mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3



How pricey are the regular books, Wayne?