I am running 3" rsc above ground across a 30' creek. I was told I needed a christy box installed on each side of the creek, what are these and how do I install them?
Christy is one of the many companies that make handhole boxes (like a minature manhole) for underground conduit / cable. It gives you access to pull or splice at junction points on an underground cable / conduit rum.
I am going to assume the rigid conduit goes into the bank of the stream on either side and a direct burial cable will go in the pipe, or a direct burial cable will be spliced to something else at those points.
So someone suggested you'll need a handhole at those splice or pull points, which is correct.
(Unrelated to the question, also assuming the cable is supported by a bridge or something because you can't span 30' with unsupported conduit, and that the poster is aware the permitting for things crossing streams can be ridiculously difficult.)
A "christy" box is a semi-buried box that has the cover exposed. Also called a "pull box" or a "quazite box" these are used to start and terminate a cable run outdoors. Usually made from a cement-base compound, they are available from local electrical supply houses.
Why, however, are you wanting to run the line above ground? The line will be vulnerable to anything being carried down the creek. Have you considered having it horizontally bored in?