What types of communication cables can pass through electrical conduit?
You just can't do it.  There are only two exceptions where you can intermix comms and mains voltage in a conduit. 


Fiber-optic cable, where the cable is entirely non-conductive, is acceptable with mains 
SCADA controls where the interlink is related to the mains equipment, or to be more precise, where all of the low-voltage wiring remains entirely contained within Class I wiring methods, e.g. power-rated conduit, and that means not coming out to a socket and continuing onward with non-mains-rated cable, i.e. ethernet is Right Out.  Examples: 


3-way retrofit smart switches, where the switches re-task the existing mains /3+ground cable to be always-hot, neutral, and a comms wire.  
Powerline monitoring and load-usage devices such as Sense, EnergyCurb, etc. These live entirely inside the service panel, and their signal lines (current transformers) are wired entirely inside mains wiring methods.  This is a great example of how there isn't any Ethernet port on the side of your service panel (huge no-no!!), instead WiFi is used, which provides the mandatory isolation.  Essentially this whole data network "lives at live voltage" and is contained thusly. 
Commercial RR7 lighting installations, where 24VAC signals throw relays to operate lighting.  
Industrial SCADA, where the controllers sit on mains power, and the interconnect is via an Ethernet/Canbus/whatever thrown into the mains conduit or raceway, and the equipment is designed to accommodate this method.  If the SCADA equipment has an Ethernet port to the "outside world", that port is built isolated and is UL-listed to that effect. 



I am assuming you are dealing with equipment that takes a lot of power, like a server rack.  If you are only hauling AC power in that conduit to feed a "wall wart" power supply that's low voltage and &lt;55W, then forget AC -- haul the low voltage.  An obvious method is PoE (Power Over Ethernet).  However you can do this with any low-voltage load, just carefully mind your voltage drop and feel free to dip into the mains electrical parts bin for the fat wires you may need.  For instance, if you need #10 wire, then use readily available, cheap, stranded white THHN, and use it for both low-voltage + and -.  (tape the ends of the wires red and black to designate polarity etc.  You are allowed to re-tape individual wires to different purposes in conduit when it's low-voltage wiring.) 

If you just can't haul low voltage, yet your load is &lt;40W, the other super sneaky way to haul low voltage while still having mains at both ends, is use two 40W thermostat transformers back-to-back, so the transmission through the low-voltage conduit happens at 24VAC.