Direct Burial or Enclosed in Conduit?

[38Chevy454]

Getting closer to having my detached garage permit approved and ready to start moving dirt and getting ready for concrete. Was starting to think more about the electrical connection.

For my electrical, I need to run about 50 ft from house to new garage, 100 amps. Is direct burial with conduit risers at each end a good way? Or should I request conduit the whole path? I also am going to run a telephone hard line, I know that can go direct burial also. Not going under any driveway or normal high traffic areas.

Direct burial will be less cost, and that is what seems to be the preferred method. It will be minimum 18 inch depth. Done by an electrician, not by me. I will add additional circuits and lighting inside the garage once it is done to save me some money; with the minimum required by the electrician to get permit signed off.

 

[BillGalbraith]

I believe that code is 24 inches down direct burial, 12 inches in conduit. I'm sure others will point out if I'm wrong on that one.

However, what I DID was to add is that when you get a quote from your electrician, get a written quote of EXACTLY what he is doing, such as a GE subpanel box with X number of slots in it, mounted on the wall HERE (place a big X on the spot). He will then run X number of circuits with a particular size wire or better, and finish trimming it (installing outlets and plates according to code), plus grounding as required by code. Make sure you specify exactly where you want the outlets, switches, and lights. Mark them on the wall, not trust the prints because they won't look at them. Specify what gauge wire they are supposed to use (12 ga for outlets with 20 amp breakers, 15 amp and 14 ga wore for lighting, etc.) Get it all in writing before he starts. Otherwise, they will screw things up, and over charge you.

Just a little FYI, my electrical installed the wrong outlets. She didn't install WR outlets (weather resistant), even though they were in weather-tight boxes, and the inside outlets were supposed to be tamper resistant outlets, which he also didn't do. They also didn't ground it according to what the inspector wanted. Normally they would use one ground rod, but this inspector wanted two ground rods and a ground plate. Don't over-specify things, but make sure that you specify that his work has to pass inspection.

 

[sberry]

24 inches direct or in plastic conduit. 50 ft wont add a lot of cost to pipe either, legal to do both ways.

 

[GarageEnvy]

Just did this last weekend. 50amp out to my shed/pool pump. 24" down is what the code is in my area. I paid about $1.93 per 10ft length of pvc and the 6 gauge for the 50 amp was .72 per foot. Total bill was about $200 for a 65' run. You'll have more in wire but the pvc is cheap and offers a lot better protection (unless you cut it with a sawzall like I did).

 

[38Chevy454]

24 inches direct or in plastic conduit. 50 ft wont add a lot of cost to pipe either, legal to do both ways.

My memory may be incorrect, could be 24 inches that I discussed with the electrician; no matter what it will be to code for here in NM. I just wanted to understand if any drawbacks to direct burial of the cable. The cable will be direct burial rated.

Thanks to all for their answers and advice.

 

[sberry]

Pipe is just protection from rocks and someone digging in the future. If you use cable it needs to be UF not NM, underground feeder. My choice is usually aluminum number 2 due to cost, you need 4 conductors and the alum uses a 90A breaker.

 

[walrus]

Pipe is just protection from rocks and someone digging in the future. If you use cable it needs to be UF not NM, underground feeder. My choice is usually aluminum number 2 due to cost, you need 4 conductors and the alum uses a 90A breaker.

PVC isn't much protection from a backhoe


Tons of direct burial cable in the ground, if someone screws it up digging alot of time you can use a splice kit to fix it, cheaper and easier than fixing pipe and pulling in new conductors

 

[Gary S]

My choice is two conduits. One for AC, and a second one for low voltage lines. Put the both in the same trench a few inches apart and you will never regret it if you ever have to change or add another wire.

 

[BoydS]

Originally Posted by Gary S
My choice is two conduits. One for AC, and a second one for low voltage lines. Put the both in the same trench a few inches apart and you will never regret it if you ever have to change or add another wire.

I agree that you should keep the low voltage and power feeder separate. Running both in the same conduit could interfer with the signal. I would run at least the phone line in a conduit as you may want to add an ethernet, serial cable or coax down the road for a computer, TV, etc. With the short run you have and being that close to the house it's not a heavy traffic area (as you stated), so running the conduit is just for future expansion.

Another thing to consider is water to the garage. You may want to think about that if your trenching the area, unless you aleady have that issue covered.

 

[Norcal]

18" unless subject to vehicular traffic, then it's 24" of cover. IMO use pipe, it's cheap insurance.

 

[Red05GT]

Any time I have a ditch open I lay conduit, and spares. It's cheaper than digging
another ditch later and it is added protection against rocks, fence builders, landscapers,
etc. For the few extra dollars it's definately worth it.

 

[sberry]

I am interested in how we figure 18 inches? If I read this correctly it is 24. Seems every inspector I have come across quoted 24 also. The exception seems to be for dwelling parking areas.

 

[KCarGuy]

I buried (3) 1" PVC runs from house to garage.
I bent all (3) into a 90, by filling 3 foot sections with sand (tight), capping the ends and heating over the grill until I could bend smoothly with out collapsing.
Empty the sand and placed in the forms.

I use (2) runs, and still have an empty line that I can pull anything that I want through it yet.

24" down...75 foot runs.

 

[hidollartoys]

I am interested in how we figure 18 inches? If I read this correctly it is 24. Seems every inspector I have come across quoted 24 also. The exception seems to be for dwelling parking areas.

Column 3 of Table 300.5 (2005 code) allows for 18", but conduit must be listed for direct burial. Schedule 80 would be listed. This is MINIMUM and 24 ' is better, and I would suspect as always it is "inspector's choice". If you are really concerned by potential damage then bury it to 36", 48"', 60". When is it deep enough?

 

[GarageEnvy]

Well I can only say that it was definitely 24" and not 23" in my area. Dug 24", put in conduit, inspector measured to the top of the conduit and made us scrape out another inch.

 

[Red05GT]

GarageEnvy, the inspectors brother must be an electrical contractor. He was just being
a ****.

 

[GarageEnvy]

Agreed but I didn't think it was wise to tell him that. We have a little situation with our inspectors right now. The county has fired several inspectors but not until mid-June or July so they're still on the job. The guys that are left are inspecting everything where they used to be specialists. I've had 5 inspections. Three were done by a guy with a serious attitude problem. It's not just me, everyone else knows this guy as well. The other guy is happy go lucky and will work with you on things to make sure they are safe without being ridiculous. Both guys are fired so I'll be getting more new people as the project continues. The subpanel in the firewall was fine with one inspector and totally illegal with a second inspector. A lot of what gets approved and what is required is totally at the discretion of the inspector you get. Consistency is a real problem.

 

[robertlynk]

Run 2 inch conduit conduit for power 1 inch for low voltage
Why so big? later in life you need more power you can pull new wire
with no hassle. also wire is cheaper the first time run larger service wiring from the start. when back filling after a foot of fill lay a strip of red warning tape in the trench so that later in life when you forget were the conduit is you don't tear it out with a back hoe

 

[csp]

when back filling after a foot of fill lay a strip of red warning tape in the trench so that later in life when you forget were the conduit is you don't tear it out with a back hoe

My trench inspection required caution tape in the trench 6" above the feed wire before any backfill. I had to use nails to attach it to the sidewalls of the trench.

 

[mrb]

Well I can only say that it was definitely 24" and not 23" in my area. Dug 24", put in conduit, inspector measured to the top of the conduit and made us scrape out another inch.

I had something like that once, was short a couple inches. Told the inspector the dirt there was being re sloped and the pipe would end up at least 24" under finish grade. He smiled and said ok.