wiring
I need to install a new grounding rod at my house and will be running the grounding conductor through an LB body and PVC conduit down to the ground.
But I also need to run a new coax cable into the house nearby, so I'm wondering whether I can drill a hole in the conduit body, install a feed-through bushing, and run the coax into the house through the same conduit? (I'd loop the coax and weather-seal it on the outside, of course).
I'd drill from the inside out.
Cut a hole in the drywall where you want the terminal. Cut the hole so that a "low voltage" bracket will fit.
If it's a 2×4 stud wall, your bit will only have to be ~5" long. Drill a hole in about the center of the drywall cut out. You can use a 3/8" installer bit, which is ~20" long and has a hole on the end to aid in pulling the cable.
Fish the wire from the outside junction, through the newly drilled hole (if you haven't already). Add ends to the cable, and connect the end at the junction box outside. Connect the other end to a faceplate of your choosing, and mount the faceplate to the "low voltage" bracket.
Finish by sealing around the cable, where it enters the wall. Use either silicone sealant, or duct seal
You have not stated any reason that would appear to prevent the obvious solution (if you consider it a problem at all) of running the network wiring along the face of the wall at the same level as the server rack, or roughly 12" below the power conduit. If the basement/crawlspace floods enough to flood the server rack you probably should rethink the location of the server rack, and in any case the cables being run horizontally higher up won't help a bit in that case.
You could also move the cables far enough forward into the room (3-4 feet, say) that they don't encroach on your shelving unit, then run them back along the joist (it's holding up a floor above if it's a crawlspace, so rafter is not the right term - those have a roof above them) to the server rack.
Despite a number of "trying to be perfectionist" scare stories about needing to keep network and power cables well-separated, the fact is that the differential pairs in Cat5 (or 6, or 7) are designed to reject interference, and that the frequency domains of networking signals and power line noise are utterly different. So, in practical terms you can wire tie (just not too tight - sharp bends are bad) the network wires to the power conduit and not have any interference problems in a typical home application.
Coaxial cable is self-sheilded by design and thus also highly unlikely to pick up any objectionable interference simply by being run next to power or network wires.
Since all you are really considering is running them parallel at a few inches distance, you will be fine doing that (do avoid a sharp bend anywhere, particularly where you turn downwards and might be tempted to yank the wire tight around the J-hook.)
While I do generally try to maintain the oft-suggested 12" separation for parallel runs when designing from the ground up, I have hundreds of feet of Cat5e that is in close proximity to power wiring in old building retrofits, and connected to switches that report error rates - and those error rates are pretty much always zero, unless there is a more fundamental problem with the cable (like rats chewing on it, a sharp kink/bend, or a bad connection at the end of it.)
Best Answer
If there is a cubic inch listing on the conduit body it may be possible.
You still have to meet the wire fill requirements the CGB or clamp, x multiplier for the largest wire size has to be added to the total count of wires cubic inch.
This is the same as modifying a listed J Box.
Your AHJ may not allow but if it has a stamped volume code has nothing stopping it.
If it is not stamped then it is not allowed to splice or modify. (Conduit body’s don’t have a approved size chart like boxes do).
Outside a cgb (cord grip bushing) that seals / clamps the wire would be required. Inside standard 2 screw clamps are ok.