I am wiring a boat lift in the Holden Beach NC area. I am running 3/4" epvc approx 80'. This is to be strapped on the joist running out the walkway over water. Water is never going to be closer than 2' from this epvc. We are in a marine environment, saltwater with plenty of rain, wind, etc. The inspector wants expansion joints installed in this run. I have always run 25' & install a 1' piece or carflex through the runs & every 25' thereafter. He says it has to be a UL approved expansion joint. I have not found a marine-weatherproof expansion joint anywhere. I have always run my pipe like this for all boat lifts-walkways. I also leave my straps loose for expansion-contraction. HELP
Expansion Joint
- Thread starter choots
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The inspector is correct... but not from the aspect of thermal expansion and contraction...
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
The correct article is 352.44 and 352.30 the one you posted is where the building has expansion joints and would even apply to RMC or other wiring methods that don't normally require expansion joints.
PVC two hole straps will allow the PVC pipe to slide within it, do not use metal conduit straps and I know many do but they will not allow the pipe to move as required in 352.30
You can find PVC expansion joints at most places that sell PVC conduit, the are basically two conduit sleeves one inside of another that allow the conduit to move, also make sure you provide a loop in the box's so the wire can also move without breaking, Carlon's web site has a chart of the recommended distance between expansion joints for the size of pipe you are using, I'll see if I can find it.
Without expansion joints if the conduit was installed when the temp was hot the pipe can shrink and either pull the fitting out of the male connector or box hub, or break off the male threads both of which I have seen, I have seen it even pull apart at a PVC coupling. when the pipe is installed when the temp is cool or cold then it can expand and sag.
Here is a link to Carlon's PDF on everything you need to know about installing expansion joints.
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352.44 is another requirement in itself. 300.4(H) is also correct. The transition from shore to pier, boathouse, etc. can easily be viewed as crossing a structural joint, especially if the sides of transition are not solidly anchored to each other (at that point)... and 300.4(H) is the only one regarding PVC that requires a listed expansion/deflection fitting.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
300.4(H) Is for all raceways that cross a expansion joint or other place where the building or structure may move as you mentioned if the dock is not ridged to the shore such as floating docks, we always use a flexible method like LMFC or LNFC as docks can move up and down as well as closer and farther away, but 352.44 is for the thermal expansion of long runs of PVC which is recommended for runs over 25' and temperatures changes of over 25? F
The statement above in red is not true as 352.44 requires expansion fittings for PVC, 300.4 doesn't even mention PVC as it Say's all raceways? in one the surface the conduit is mounted on moves, in the other the conduit itself move from thermal expansion, I believe the inspector in the OP is requiring the expansion joints for thermal expansion as the way it is worded.
Here we also have to have one for ground heaving when we come out of the ground and into the meter socket because of the frost line
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
After re-reading the OP I see this is over salt water which will have up and down tide movements as I would believe it would be a floating dock? I would not use a slip expansion fitting from shore to dock as it would not provide for the up and down movement, a flexible method would most likely have to be used at this point, for thermal expansion because of the temp changes in the location which could be as low as 0?f to as high as 100?f which would require at least one expansion joint between any fixed box's over 25' apart or one in the 80' run, as you would have almost 4" of expansion (more like 3.80") in 80' of conduit or just at the limit of one expansion joint, Carlon's expansion joint max travel are 4" from ?" to 1? conduit and 8" for 2" and above conduit.
My statement, in red, is true. 300.4(H) is regarding all raceways. Are you saying PVC isn't a raceway???
Maybe you are misinterpretting my point, and/or perhaps I am not making my point clearly. I tend to be succinct, while from my perspective you tend to be a bit wordy.
352.44 requires exapnsion fittings for straight runs between securely mounted items. If as stated in the OP, a 1' section of Carflex is inserted in the run every 25', then the straight runs (of PVC) do not exceed 25' and they are not between securely mounted items (assuming Carflex is not securely fastened). That makes 352.44 moot under the conditions of installation.
As for using a flexible wiring method at the shore to water-structure transition, note 300.4(H) says "or other approved means"... which means it is at the discretion of the AHJ whether the other means is acceptable. Even with first hand observation of the installation, my opinion don't matter... but I would likely approve it if I were in that position.
Another thought is, one expansion fitting can serve a dual purpose in compliance with both 300.4(H) and 352.44.
And that falls under 300.4(H) in conjunction with 300.5(J) ... not 352.44.
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
I agree PVC is a raceway and is covered in 300.4(H) as being required to have an expansion joint across a point of expansion in a structure, guess I wasn't trying to disagree with you but trying to point out that because of the way he mention that the run was 80' I took it as the inspector was rejecting the car flex which we both know that it is also an accepted method because 352.44 only require the expansion joint for straight runs between fixed mounted items
Ya been accused of writing a book or two when I respond, I have a bad habit of trying too hard to make sure someone understands what I'm trying to say or not sure if the poster is understanding , so I tend to ramble too much:ashamed1: but when you posted the reference to 300.4(H) I couldn't figure out the reason as with tidal movement or up and down movement a linear expansion joint would not be a good choice from land to a dock, guess my response could have been worded using much less words LOL
Correct unless the inspector is thinking the car flex (LNMFC) is subject to damage? even a 90? turn up into a box can eliminate the requirement of an expansion joint as the pipe can expand some if the pipe hasn't been strapped right at the 90? point we see this type of expansion system used in steam lines all the time, but without the reason or the thinking of the inspector who knows?
Again just a linear expansion joint at the land to dock point will not provide for up and down tidal movement or waves which would eventually break the pipe, not a good design choice, I wired many docks in Florida which has probably the least amount of tidal change with going farther north having more as you get north, and we always provided a flexible method at the point of transition from land to dock, unless the dock was of a stationary non-floating type, but then if it were a fixed type then there would be no reason for any expansion joint as being that both are mounted to land and the fact that the land should not move in reference to each other then the only consideration would be thermal expansion, we had coated RMC that would come right out of the concrete wall that a fixed dock was bolted to and run right onto the dock and never had a problem, well until Hurricane Andrew hit my dad's place, which is not a normal situation and a expansion joint would have not helped because the dock was gone
I guess this was the part that I didn't understand why you sited 300.4(H)
Very true, anytime you can use one item for dual purpose it always saves money
correct more so to the requirement of 300.5(J) if 300.4(H) covered it then why the need for 300.5(J)? to me the requirement in 300.4(H) is more for where a raceway crosses two point of a building or structure that the structure can move or expand but the raceway doesn't, where the raceway can expand but not the structure then these requirements will be in their respective article for the raceway such as 352.44 which I'm not sure but is about the only type of raceway I think the NEC requires an expansion joint for thermal reasons? I couldn't even find any requirements for other non-metallic raceways which is kind of strange, you would think that Aluminum RMC would have some kind of requirement for thermal expansion?, I know at work you can hear the aluminum conduit making a kind of popping sound as it moves under the u-bolts we use to secure it, at night when it gets cooler.
For some reason I have always thought even RMC had some kind of expansion requirment for really long runs as I remember installing expansion joints on very long runs?? but at quick glance I didn't find any.
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I agree with most of your post. So only have a couple comments...
Mounted to land seems to eliminate the need... but it depends a lot on whether it is the same chunk of land. Your example regarding frost heave is a prime example. The chunk of land the building is referenced to is its footing. The chunk of land the horizontal portion of the conduit run is referenced to is likely above the frost line and progressively remote to the building's footing. While the building's footing isn't supposed to move, it can and does in many cases. Transitions between land and dock probably vary more in design than land to buildings.
See 300.7(B)
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Most likely correct in non-commercial type installations or where the dock is not very well supported and or where it is a freshwater lake or river where in the winter the ICE could cause the dock to move and I would have to agree with you on those points as well as ground heaving, but salt water which is a little more resilient to freezing and being that this is in North Carolina which I don't think I have ever seen the salt water in the sound around Harkers Island N.C. ever freeze since the temps of that area never get as cold as it does here I don't think the freezing would be a problem but the NEC is world wide so we must keep an open mind as how it can apply to areas we might not have seen the conditions that the reason one might have to apply it in.
The several ridged docks that my dad had at his marina were quite ridged with 8" Steel pipes driven 40' into the sea bed then filled with hydraulic concrete, and two of them were the runways for a huge 400 ton rated Grove gantry crane with 4 hoist which we used to lift boats up out of the water for repair or dry docking, it had 4 large passenger jet tires on it, all the fixed docks we had were concrete surfaced, so not much movement with these, but I can definitely see your point with wooden docks and wooden pilings.
Guess it would be a judgment call on a case by case bases.
I knew it was in there somewhere, Thank's
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