Actually there are a variety of systems: Hot Oil, Steam, Hot water,Electrical, etc.
The fluid/steam systems employ a supply line (from the header) to a supply manifold, leads (pre-insulated tubing)to the traced line, tracing (bare) tubing to a max of 80 LF or so and a return (condensate in the case of steam) to a return manifold and back to a return header.
Electrical systems are really a second choice except in the cases where the Process requires finite ranges of temperatures to be maintained or there is no readily available fluid/steam supply source. Discharge for fluid/steam can always be made to the ground in remote plant areas. Electrical tracing systems are more expensive on an ongoing basis.