PVC expansion coupling

[Mdsparky]

2" PVC riser 7' to a 45* bend up a rake board 12' to a weather head . Inspector asked where my expansion coupling was . I told him there is only one fixed point . He replied " you have a change of direction with the 45* bend " I said it is free to move . He said he'd let it go this time . I don't believe it to be a violation. What say you ?

 

[LarryFine]

Not needed.

To me, the direction change lessens the need.

 

[rc/retired]

Agree. Not required for a change in direction.
Section 352.44 requires an expansion fitting for thermal expansion and contraction.

Ron

 

[kwired]

Only need expansion fitting if there is support close enough to the bend that it makes it "immoveable" so to speak. This becomes more of an issue with full 90 degree bend than for a 45 degree bend.

 

[Fred B]

2" PVC riser 7' to a 45* bend up a rake board 12' to a weather head . Inspector asked where my expansion coupling was . I told him there is only one fixed point . He replied " you have a change of direction with the 45* bend " I said it is free to move . He said he'd let it go this time . I don't believe it to be a violation. What say you ?

Do the math for expansion at temp variation per 352.44, if it expansion is less than allowable then provide to inspector.
an Elbow is a "securely mounted item" per code. But also starts over the calculation for a "straight run".

"2017 NEC 352.44 Expansion Fittings.
Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44, is expected to be 6 mm (1⁄4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations."

 

[kwired]

Do the math for expansion at temp variation per 352.44, if it expansion is less than allowable then provide to inspector.
an Elbow is a "securely mounted item" per code. But also starts over the calculation for a "straight run".

"2017 NEC 352.44 Expansion Fittings.
Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44, is expected to be 6 mm (1⁄4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations."

Elbows are not necessarily securely mounted though. Is possible to arrange your securing so that the elbow has room to move.

If you actually secure the elbow or immediately adjacent to it, then you likely must consider it fixed or at least fixed in one direction.

 

[Mdsparky]

Do the math for expansion at temp variation per 352.44, if it expansion is less than allowable then provide to inspector.
an Elbow is a "securely mounted item" per code. But also starts over the calculation for a "straight run".

"2017 NEC 352.44 Expansion Fittings.
Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44, is expected to be 6 mm (1⁄4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations."

I guess I don't view the 45° bend as a fixed elbow the clips are designed for the pipe to move beneath so I maintain I have one fixed Point

 

[Fred B]

I guess I don't view the 45° bend as a fixed elbow the clips are designed for the pipe to move beneath so I maintain I have one fixed Point

Need to write for a code change to indicate any standard elbow less than 90 deg is not an elbow for purpose of this section if you desire to not count the 45 deg elbow. Don't forget substantiation.

 

[LarryFine]

Need to write for a code change to indicate any standard elbow less than 90 deg is not an elbow for purpose of this section if you desire to not count the 45 deg elbow. Don't forget substantiation.

Doesn't that mean it would have to be treated like one continuous straight length?

 

[Mdsparky]

Need to write for a code change to indicate any standard elbow less than 90 deg is not an elbow for purpose of this section if you desire to not count the 45 deg elbow. Don't forget substantiation.

It's the "securely" mounted piece I have an issue with. When I glued the 12 ft piece into the 45* it moved under the clip . It is free to move there is only one fixed point , is my point.

 

[wwhitney]

So the geometry here is: Fixed point (Equipment) -- Vertical run -- 45 degree elbow -- Diagonal run -- Weatherhead (free move, not a problem for the drip loop).

PVC straps are designed to accommodate axial movement of the conduit, but not transverse. With a 45 degree elbow, thermal expansion can absolutely put stress on the conduit/straps when transverse movement is not accommodated. When the vertical run wants to expand 1", then each strap on the diagonal run should move 1" upwards. That's equivalent to moving 0.71" axially (no problem) and 0.71" transversely (a problem, the pipe is constrained).

Conversely, expansion of the diagonal segment is not a problem--it can expand relative to the elbow, with all the movement taken up by the weatherhead.

352.44 requires an expansion fitting when the length change is 1/4" or more. So what is the temperature swing in MA? If it's 100F, Table 352.44 says that 100 ft of PVC will move 4.06", or 7 ft will move 0.284". Just over 1/4", so you could argue that an expansion fitting is required in the 7' segment.

On the other hand, because the 45 degree elbow will cause the diagonal segment to only see 71% of the transverse movement that a 90 degree elbow would cause, you could argue that the above computation should get a further factor of 71%, which gives 0.202" of movement, less than the 1/4" threshold.

Cheers, Wayne

 

[LarryFine]

Sounds like the solution is a strap just below the 45, and the next one several feet up the slope.

 

[wwhitney]

Sounds like the solution is a strap just below the 45, and the next one several feet up the slope.

That's not going to help in and of itself. The transverse displacement of the pipe at the strap "several feet up the slope" is still going to be determined by the length of the vertical run below the 45. I think the OP's install is fine without an expansion fitting, because that transverse displacement is under 1/4", because the elbow is a 45 and not a 90, so the transverse displacement gets a factor of 71%.

But if the two lengths were reversed, with a 12' vertical and a 7' diagonal, then you'll need a strap on the diagonal section because 2" PVC needs straps every 5', and that strap will be trying to restrain a transverse displacement of 71% * 12/100 *4.06" = 0.35", more than the 1/4" threshold of 352.44. So you put an expansion fitting on the vertical section.

Cheers, Wayne

 

[Mdsparky]

Good argument Wayne. Thank you.