FAQ: What is the difference between above ground and below ground conduit?
The main difference is in fire resistance. Above ground conduit has fire resistance per UL2515 and CSA C22.2 No. 2515 standards, meaning that the conduit will self-extinguish within 15 seconds after each of five successive flame applications per the UL 2515 flame test standard.
Below ground conduit meets UL94 HB (horizontal burn) requirements, which aren’t as stringent as vertical burn requirements. This also means that conduit manufactured and labeled for “above ground” applications can be used for “below ground” applications.