**No—you can change from RMC to EMT inside either building.** EMT is generally cheaper and easier to install, and it is permitted in walls and ceilings where it isn’t subject to severe physical damage. Use a **listed RMC-to-EMT transition coupling** that matches your threaded or unthreaded rigid conduit. [Southwire’s transition fittings](https://www.southwire.com/electrical-components/commercial-industrial-residential-fittings/1-1-4-emt-to-rigid-combination-compression-couplings-steel/p/RTE125) are an example.

Electrical PVC conduit is another indoor option where permitted, but **grounding affects that choice**:

- Assuming your three #6 wires are two hots and a neutral, a properly bonded, electrically continuous **RMC/EMT system can serve as the equipment grounding conductor** under the NEC.
- If you introduce PVC, you must provide a wire equipment grounding path and bond the metal portions. For a standard 60A feeder, that is ordinarily at least **#10 copper**, in addition to the three feeder conductors. [Grounding conductor rules](https://codes.iccsafe.org/content/MIRC2015P2/chapter-39-power-and-lighting-distribution), [grounding conductor sizing](https://bsd.dli.mt.gov/_docs/Training/DAY-2-of-Residential-Electrical-2-day-course-WC3-2020-NEC.pdf).

For the trench, **IMC is another option to price**: like RMC, it generally permits six inches of cover in ordinary yard locations. PVC generally requires 18 inches. Six inches means soil **above the top of the conduit**, and driveway crossings have different requirements. [NEC burial table](https://sfgov.legistar.com/View.ashx?GUID=E7387698-D153-4FA8-AB25-4C4495FB80F3&ID=4672186&M=F).

Also, use wet-rated conductors such as **THWN-2** underground. At the shed, keep neutral isolated from ground and provide the required grounding electrode system; ground rods don’t replace the feeder’s equipment grounding path. [Underground wiring rules](https://codes.iccsafe.org/content/IRC2021P3/chapter-38-wiring-methods), [separate-building grounding rules](https://codes.iccsafe.org/content/UTRC2021P1/chapter-36-services).

These are NEC-based rules; confirm your locally adopted requirements before buying materials.