Running electrical wire through PVC pipe

Page 3 of 4  


I don't believe the 60% fill limit applies to sleeves, only short sections of a complete conduit system. The way I think of sleeves, they are not part of the electrical system. If the installation is NEC-compliant without the sleeve, then the presence of the sleeve doesn't change anything, it was just an aid in installing the cables.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 1 Mar 2010 21:12:26 +0000 (UTC), Wayne Whitney

The real question is what your AHJ thinks. It says "nipples less than 24 inches", not conduit systems. In this jurisdiction that is what you call a sleeve. If this is a conduit system you can't exceed the fill in any of it.
Also there are plenty of AHJs who say if you pull wire in it, you need to use a listed raceway. I have seen 4" white PVC pipes under driveways failed because they pulled a 14/2 UF in it. Personally I don't agree with that one. It doesn't matter. If that was my AHJ I would be using RNC. The attitude is that they make the appropriate raceway and that is what you should be using.
Be careful to call these things ducts when you are talking to an inspector since that is acknowledged in the code but not defined or regulated. It might give you a better case.
As for sealing, find out if they want "draft stopping", "fire blocking" or"Fire stopping" (3 different things). They would require different materials for each. Draft stopping could just be spray foam, Fire blocking might be as simple as fiberglass insulation packed in the cavity or closely fitting wood members but that is up to the opinion of your AHJ. Fire stopping is a listed assembly of components with a fire resistance rating based on time.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

In the NEC 2008, Chapter 9 Table 1 gives the conduit fill allowances. Note 2 says "Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections of conduit or tubing used to protect exposed wiring from physical damage." So it doesn't apply to sleeves.
Note 4 says "(4) Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, . . ." So this is relaxing the Table 1 requirements for certain parts of a conduit system, it does not apply to sleeves.

Yes, it is completely illogical to say "this installation would be compliant if that piece of PVC pipe weren't there, but now that it is, it is in violation".

Good idea.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wayne Whitney wrote:

Well ain't that interesting. IMHO it conflicts with 322.22 for PVC conduit (and xxx.22 for most other raceways): "Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9"
============The 2002 NEC change proposal (for xxx.22) came from the code writing panel and says very little about why the change was made. The explanation is the change "clarifies that cables, where permitted elsewhere in the code, are allowed to be used in a raceway." The language was later changed to "where such use is not prohibited".
============ From the NFPA/IAEI code changes book: Using raceways as isolated protective sleeves for cables was accepted in the past.
It appears that the proposal may be for raceways that are connected to the electrical system on one end. There are 2 examples shown.
One example is a box with a receptacle that has a conduit out the top and has a Romex run through the conduit into the box. The top of the conduit has a conversion fitting with a Romex connector. [It is common practice to use essentially the same arrangement, without the Romex connector, to protect exposed Romex.]
The other example is for one or more Romex runs into a panel through a conduit as allowed in 312.5-C. ============== Seems like the application, as written, would be Table 1, Note 2 applies in general but 322.22 applies specifically to all uses of PVC conduit. But most raceways have an xxx.22 section, so I don't know what Note 2 applies to. Not likely that is what was intended.
If Table 1, Note 2 applies to all raceways that protect from physical damage that leaves isolated raceways, as used in this thread, covered by xxx.22 (which may or may not have been the intent).
This is unreasonable ambiguity. I guess the answer is ask the inspector.
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I would say that Note 2 is part of Table 1, Chapter 9, so that the 322.22 reference includes Note 2. I don't see the ambiguity.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Oops, that should be 352.22 for PVC conduit.
Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wayne Whitney wrote:

That works.
For the "sleeve", it is not intended to protect from physical damage, so fill restrictions apply via 322.22 to Chapter 9, Table 1. Heat is as much a problem as full wiring systems.
Also wire ampacity derating applies, as you wrote long ago.
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well we are still reading "Note 2" differently. The first half of the sentence already exempts all sleeves. The second half of the sentence elaborates and gives a specific example but doesn't in any way limit the first half. The upshot is that all sleeves are exempt.

Right, and that is handled by the derating requirements when bundling, not by conduit fill. Conduit fill is for protection of conductors from damage during installation.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wayne Whitney wrote:

I do read it different. IMHO Note 2 is taken as a whole and not split into 2 sections. If the first half is independently applied, the second half is not necessary.
Some of the other notes (5 and 9) are specifically for cable, which would not likely be used in "complete conduit ... systems".

I figured out temperature was the wrong limitation right after I hit Send.
As you said, the point of Table 1 is to prevent damage to wiring at installation. By your reading of Note 2, there is no limitation on the number of cables that can be fished into a sleeve, and no protection from installing too many cables. The limit that would protect a "complete system" would not apply to a sleeve.
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I see the second half of the sentence as only an elaboration and explicit identification of the most common case of the first half. It is like saying "Crash test regulations apply only to vehicles with 4 or more wheels and are not intended to apply to motorcycles." That sentence means to me that crash test regulations do not apply to vehicles with 3 wheels.

That's correct, but I don't see any problem with that. Cables have an overall jacket that will help protect the conductor insulation from damage. And a sleeve is likely to be a shorter run which would require less pulling force than many "complete system" installations.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bud-- wrote: ...

The Note does not supersede nor provide relief from the general workmanship clause to cover flagrant abuse of the privileges granted therein.
--


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wayne Whitney wrote:

352 Rigid PVC conduit "352.22 Number of conductors .... Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9."
Identical language was added to most raceway articles (xxx.22) in the 2002NEC, probably to make existing practice clear. I would expect inspectors would apply the same fill restrictions to PVC water pipe (if they allowed water pipe). I haven't tried, but it would probably be difficult to pull in Romex that did not comply with the fill restrictions.
The NEC doesn't specify a length or reason for using PVC conduit.
Fire stopping might actually be enforced by the building inspector (not electrical inspector).
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well now I'm confused... :) At what point does does conduit become a full "conduit system" that restricts NM cables in the conduit?
When I tried to decipher the code a couple years ago, I understood it to mean "short" sections of conduit (i.e. 4 feet or less) where at least one end was open for air flow was OK. Wouldn't a long "sleeve" of conduit (say 20 feet long from basement to attic) encounter the heat buildup the restriction is trying to prevent?
I'm not trying to be sarcastic, I just don't understand what the deciding factor is for NM cables in conduit. It would be good to know for future work.
Thanks,
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

When you want to use that conduit system for its normal purpose, to be able to run individual electrical conductors like THHN, XHW, etc. In that case, you have to count any NM cables also in the conduit towards the conduit fill.
If you just have a sleeve or guideway for cables, like a piece of pipe with open ends, then conduit fill does not apply, in my opinion. But see my other post for the restrictions about supporting the NM cable.
BTW, there is obviously some variation in understanding about this issue. So if you are planning to do this, you might want to check with your inspector first. [If they say it is not allowed, you could ask them what NEC article it violates.] You might find yourself in a situation where your inspector disagrees and you decide it isn't worth challenging.

Conduit fill and derating are two different things. Conduit fill is about avoiding damage to the conductors while installing them (cables already have an outer sheath to help with that), while derating is about keep the conductors from overheating when multiple conductors are in close proximity.
BTW, you could have a derating issue due to bundling of cables without any sleeve. E.g. if you drill a series of holes in a stud wall and pack a bunch of cables tightly together through the holes (such as more than 4 12/2 or 14/2 NM cables), that could be derating problem. Certainly it would be if you also cable tied the cables together in between the studs.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

In fact, in the 2008 NEC, you have to derate any time you have more than one cable going through a hole in framing that will be sealed with thermal insulation, foam, or caulk. NEC 334.80 says, in part:
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wayne,

Thanks for the clarification. I appreciate it!

So far, the only conduit related issue my inspectors have been concerned with is bushings on the open ends of the conduit to prevent the conduit from chafing the cables.
On a related note, I wonder how an open two story vertical run of conduit would be viewed from a fire spread point of view? Our building inspectors were strict about sealing all openings at floors and ceilings to prevent fire spread. It seems like an uninterupted vertical run of conduit would act a lot like a chimney, allowing a fire on the lower level a straight path to the top floor (or attic).

I was surprised to learn on my last inspection that it was actually OK to run two cables through the same clamp on the breaker panel. It may pass inspection, but it didn't seem right to me. I prefer one cable per clamp.
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, that is a good idea, and in certain code sections is called out explicitly.

I would expect it would be required to be fire caulked. My building inspector required every penetration of top and bottom plates to be fire caulked. Where I used EMT to sleeve NM cable for protection from physical damage in a thin (2" framing) wall, I used bushings and caulked the openings.

Are you talking about clamps that you installed in a KO on the panel? The manufacturer's packaging or instructions should specify what combinations of cables it is to be used with.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That seems like it would make future additions more difficult, having to dig out the caulk before a new cable could be run. I wonder if a junction box at the top and bottom would serve a similar function, but still allow easy access in the future. Just thinking out loud...

Yeah, sorry for the vague description. I always use one clamp per cable in the knock-outs, so it didn't even occur to me you could run more than one. I was really surprised when the inspector said I could if I needed to.
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I used underground rated PVC of 2.5" to run cable to my shop. It was done by a licensed electrician. Are we talking about sprinkler PVC, or electrical rated PVC?
Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hi Anthony,
Thanks for your response. I am not familiar with the term "Romex" cables. The electric wire I run labeled as 12-2 NM-B With Ground. I do not know if it is romex cable or not but it does not mention romex anywhere on the packaging as far as I can see. But I will google romex and see what I can find.
I have already purchased electrical conduit to run a 1 1/2 diameter line from the basement for electrical and another 1 inch conduit for data stuff.
I am going to have speakers at the other end of the room from the computer and mixer so I think I will run conduit up the wall and over the ceiling for those wires in case I want to change those someday. And I will install two Cat5 data outlets. One on each end of the room. I think I will run conduit for those lines too because data wire requirements change so much.
Thanks, David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.