I have a long run (1300') of PVC for some decorative lighting along a driveway. The lamps will be spaced about 130' apart. I'm wondering what the experience is regarding expansion/contraction of the PVC conduit. I know the temp down at 4' or so is pretty constant, but at 2' I'm not so sure it's constant. I certainly don't want any fittings to pull apart. Above ground, expansion fittings would be mandatory.

InspectorE,
300.5(J) ground movement,
and 300.7(B) expansion fittings.
I'm assuming that you are in a zone 3 or 4.(did a google on "frost zones")
I personally probably would not bother with the expansion fittings if you can get down to 48"...like you said, it should stay a constant 55°
anything less than 4', I would put one every 50-100'. 352.44(A) (let's say in the summer the earth is an even 55°, and in the winter it is 32°., so 1.01 inches per 100'.)

for conduit that is buried, you will not have to be concerned about expansion fittings.

Pierre

Check Carlon literature, UG is OK without exp. joints. But, you must be stubbing 'up' at the fixture locations, No??

You may get ground heaving conditions by/at the stubs.

BTW, if you have concern, I do not know of any prohibition (NEC) or mfg that says you cannot install exp joints if you want.

John

There will be lantern posts (5' high or so?) every 130'. Since it is underground, it has to be wet rated wire, so I'm not too concerned about any leakage/condensation inside the conduit. Stubs will have to be brought up to the posts, that's correct. Fortunately, the lamps are only 25 w or so, the voltage drop won't be a big factor.