Are conduit bodies marked with their volume by the manufacturer allowed to contain splices?

Conduit bodies that are marked with their volume by the manufacturer are indeed allowed to contain splices if they are appropriately rated for that purpose. The National Electrical Code (NEC) provides guidelines and requirements regarding the use of conduit bodies, stating that if a conduit body has a listed volume that meets or exceeds the minimum requirements for the conductors being installed, then splices can be made within it.

It's important to note that splices must be made in a manner that maintains the integrity and safety of the electrical installation, following the NEC's broader requirements for junction boxes and enclosures. The concept of their being marked with volume ensures that the electrician or installer can confirm that the conduit body can accommodate the physical and connection requirements of the conductors, thereby allowing for safe and compliant installations.