This is what happens when the expansion fitting is NOT installed. The side of the box was pulled completely out. These were taken in a parking garage that is being renovated. The metal conduit will probably be replaced by rigid non-metallic conduit sched. 80 WITH expansion fittings.
This is the second of two pictures showing an expansion fitting on rigid conduit. This is how it should be done.
I understand the reason for expansion fittings, but never really saw an install where I was thinking "They'd really be up a creek if they hadn't put that expansion coupling in." Now here's a dramatic example of what happens when you don't. Neat.
There's a run of 3/4 galvanized that runs along a fenceline for about 1200 feet out where I work (For H2S monitors) In the cold, it's straight as an arrow, but once it gets above about 80F or so... It starts doing the wave... along the WHOLE run!
The coefficient of thermal expansion for steel is 0.00000645in/in/deg. Doesn't sound like much, but for a 100' piece of pipe, the difference between a -20F day and a 110F day is 1". Aluminum expands twice as much as steel. Concrete is practically identical to steel. (Convenient for rebar, eh?) BUT, if that concrete has expansion joints, and the steel doesn't...
PVC is far worse, as it has a much higher coefficient of expansion. A similar piece of RNC would have an appx 4.5" expansion/contraction.