What circuits is 10/2 NM-B used for?

It is for 30-amp, 240-volt circuits such as electric dryers, ranges, water heaters and some subpanels. It has two current-carrying conductors plus a ground.

Can it be used outdoors or underground?

No. NM-B is rated for indoor, dry locations and must not be buried or run in wet areas. Use UF cable for underground or outdoor runs.

Is 10/2 the same as 10/3?

No. 10/2 has two conductors plus ground; 10/3 has three plus ground. Use 10/3 when a circuit needs two switched hots or a neutral, such as some dryer and range setups.

Does it need conduit?

Not inside walls, ceilings and floors where code allows NM cable. It does need protection where exposed, such as conduit sleeves through masonry or where subject to damage.

What does the ground wire look like?

The bare copper ground runs alongside the two insulated conductors inside the jacket. Connect it to the grounding terminal at both ends.

Can I run it through attic insulation?

Yes, where the cable is not subject to physical damage and local code permits. Keep it away from heat sources and follow ampacity rules for bundled or insulated runs.