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I'm running 2" PVC from my house to a detached garage to run a 60 amp feeder. Looking at the NEC, it looks like I need to put it in SCH 40 below-ground. However, it looks like I have to use SCH 80 anywhere the PVC will be above the ground. Is that correct, or can I get away with using SCH 40 for the whole run?

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  • When I ran power to my shed about 10 years ago I used EMT. It was about as cheap as PVC and I don't have to worry about anyone accidentally digging and hitting a live wire. I put it down about 2 feet. No problem to date.
    – getterdun
    Feb 12, 2014 at 4:56
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    The guy who said he installed 2" EMT 24" deep is wrong. EMT is not rated for underground work. This conduit and fittings will corrrode. Sorry for the bad news. Raul Electrician Oct 15, 2017 at 6:28

6 Answers 6

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National Electrical Code 2014

Article 352 - Rigid Polyvinyl Chloride Conduit: Type PVC

II. Installation

352.10 Uses Permitted. The use of PVC conduit shall be permitted in accordance with 352.10(A) through (H).

(F) Exposed. PVC conduit shall be permitted for exposed work. PVC conduit used exposed in areas of physical damage shall be identified for the use.

(G) Underground Installations. For underground installations, homogenous and nonhomogenous PVC shall be permitted for direct burial and underground encased in concrete. See 300.5 and 300.50.

Article 300 - Wiring Methods

I. General Requirements

300.5 Underground Installations.

(D) Protection from Damage. Direct-buried conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4).

(4) Enclosure or Raceway Damage. Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC conduit, or equivalent.

352.10(F) says that the PVC conduit "used exposed in areas of physical damage shall be identified for the use". I know schedule 80 is suitable for protection from physical damage, however, the Authority having jurisdiction in your area may allow schedule 40 as well. You'll want to check with your local inspector to be sure, or use schedule 80 for the exposed section.

300.5(D)(4) says that even though the conduit is buried, if it's subject to physical damage (not deep enough, under a garden, etc.) it still has to be schedule 80.

UL 651

Schedule 40, 80, Type EB and A Rigid PVC Conduit and Fittings

1.2 Schedule 40 and 80 conduit and fittings

1.2.1 Schedule 40 rigid PVC conduit and fittings are for aboveground use indoors or outdoors exposed to sunlight and weather, and for underground use by direct burial or encasement in concrete. Schedule 40 rigid PVC conduit, elbows, that are specifically marked for underground use are suitable for use underground only by direct burial or encasement in concrete.

The UL listing says both 80 and 40 can be used in both above and underground installations.

Guide Information for Electrical Equipment The White Book 2013

Rigid Nonmetallic PVC Conduit (DZYR)

Use and Installation

Schedule 40 conduit is suitable for underground use by direct burial or encasement in concrete. Schedule 40 conduit marked "Directional Boring""(or "Dir. Boring") is suitable for underground directional boring applications. Schedule 40 conduit is also suitable for aboveground use indoors or outdoors exposed to sunlight and weather where not subject to physical damage. Schedule 40 conduit marked "Underground Use Only" is only suitable for underground applications.

Schedule 80 conduit has a reduced cross-sectional area available for wiring space and is suitable for use wherever Schedule 40 conduit may be used. The marking "Schedule 80 PVC" identifies conduit suitable for use where exposed to physical damage and for installation on poles in accordance with the NEC.

The White Book clearly states that only schedule 80 is suitable for use where exposed to physical damage, though again, says schedule 40 is suitable for aboveground use (unless labeled otherwise). So while you may be able to use schedule 40 for the entire run, you'll have to use schedule 80 through any areas where the AHJ deems the conduit is exposed to physical damage.

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  • Where are you finding the code to copy and paste? Is that some subscription or something you have to pay for? Oct 13, 2017 at 17:45
  • @JoePhillips who says I'm copying and pasting?
    – Tester101
    Oct 13, 2017 at 22:00
  • Oh dear. Even better. But seriously, where can a regular like me find the actual code? Do I have to buy a book? Oct 14, 2017 at 0:38
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    @JoePhillips You can get free access to NFPA 70, you just have to sign up for account. It's not mobile friendly, so best to view it on a computer.
    – Tester101
    Oct 14, 2017 at 1:16
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I asked the local inspector, and he said SCH 40 is fine for both above and below ground. I ended up using 2-2-2-4 Aluminum (marketed as mobile home feeder) to support the 60 amp service.

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I just got off the phone with my electrical inspector (in Tennessee they are state-certified). Sch. 40 PVC is okay underground (18 inches down in a residential yard), but 80 is needed for the section that comes above ground. An exception is if you use the Water-tite continuous flexible conduit because they don't make that in 80.

A UL listing for above ground use (of Sch. 40) doesn't necessarily mean that NEC approves that use. In academic terms, the UL listing is necessary, but not sufficient. NEC has to say okay, too.

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    Note that many expansion joints and slip risers are only effectively Schedule 40 in wall thickness, so if you need Sch80 stubups, then you'll have to chase down Sch80 expansion fittings to match (the regular ones will fit just fine, they just won't have the same damage resistance as the rest of the stubup) Mar 5, 2021 at 23:40
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If the NEC accepts schedule 40 at which ever depth under which ever weight or ground type… running schedule 80 pvc is literally throwing your customers money or the job out the window when bidding.

If you plan on digging it up yourself with a bobcat than you already know the depth. If you’re worried about future owners of area digging it up, place identification tape 12” above the conduit.

Schedule 40 is pretty strong when below 2’ underground. How would it break?

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Not true. NEC is not the end all be all some think it is. Municipalities don't have to accept what the NEC says, in fact the NEC is not even a legally enforceable entity, I don't have to do anything they say unless my local code says so.

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    While true, this is a somewhat deceptive statement. Most (all?) localities in the US adopt some version of the NEC. Many adopt it wholesale and verbatim, others make minor or major adjustments (ex: Chicago requires pretty much all residential wiring to be in conduit) to it, but all locals codes are based on the NEC in large part. Where I live, we're still on the 2008 version, but it's still based on NEC.
    – FreeMan
    Apr 15, 2021 at 13:10
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    What you just said is true of all codes. None of them come from "legally enforceable entities" (not even sure what that means, really). NFPA, IRC, IBC, NEC etc are all just standards made by various nonprofits and then adopted as law/ordinance in various jurisdictions. But just as much to the point the NEC is written by experts in the field who know more than anyone on this forum. We should all want to meet NEC code even if our local jurisdiction has a lower bar.
    – pbristow
    Apr 15, 2021 at 16:10
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No one can make exceptions or go below the standards of the NEC period. The NEC is the minimum standardized electrical installation code. The local or state ordinance can only make the NEC code stricter with ordinances. For instance the NEC says that 1 inch emt must be strapped within 3 foot from a junction box. The city ordinance may say it has to be strapped within 18 inches of a junction box. The city ordinance can not say it can be strapped within 4 foot of a junction box. No inspector can weaken the NEC code book for it is already minimum standards.

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    That is NOT true -- while inspectors don't have exception power as you say, an AHJ can choose to not adopt code provisions even if not adopting them would make the as-enforced code less strict than the NEC. (This is a significant bugbear of the NFPA WRT non-adoption of the more recent/aggressive AFCI and GFCI reqs) Mar 5, 2021 at 23:40
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    @ThreePhaseEel is exactly right. Take a common example in the IRC - the requirement that residential homes be built with sprinklers now. Many states adopt the latest IRC but specifically eliminate this requirement, even though it was added to the IRC quite a few years ago.
    – pbristow
    Apr 15, 2021 at 16:12
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    @pbarranis -- it's one of the most irksome examples i know of -- the benefit/cost tradeoff for sprinklers is extremely clear to the point where I see them as "the best fire insurance money can buy". People who harp about water damage don't understand two things: 1) that wetting is far more reversible than burning and 2) that if a working fire gets into the structure (wall and floor cavities) of any house built after oh, the 1970s -- that house is pretty much a gone gosling, even before you add 250GPM hose streams to the mix. Apr 15, 2021 at 23:04

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