Can I run conduit in an open ceiling on top of the bottom part of the rafters in a commercial building?
You can run most any rigid, PVC and or EMT conduit as this is a dry location it will need to be secured within 3' of the box and depending on size anchored to the rafter every 10' feet. I just double checked the support for PVC in the smaller size is 3', I don't use PVC very often but it is very easy to install. Code may require this to be done by an electrician because it is commercial. A home owner can do all there own work but when it goes industrial or commercial depending on local code it may require a licensed electrician.