how do you isolate a section of track for the next?

It depends on the type of track you are using.  If you are using tubular track, remove the steel track pin and insert a plastic track pin between the center rail of the switch and the track where they join.  If you are using Atlas or Gargraves, use a Dremel or hacksaw and cut through the center rail (of the track, NOT the switch).

Curt

Which rail do you want to insulate? Answer depends on track type as well.

With Gargraves track all rails are electrically insulated from each other, so all you do is pull the track pins from each end of the section of track to insulate that rail section.

I would suggest using fiber pins with Gargraves to keep proper track alignment.

Lee Fritz

To completely isolate the section, you need to put plastic insulating rail joiners, or cut gaps in all 3 rails.

Generally in 3 rail, guys will just insulate the center rail - the outside rails dictate common wiring.   

It depends on what you want to do.

I might be getting somewhat side tracked here, but I use Gargraves track and older Lionel two light signals on my layout. What I do is to run the hot wire to the signal light and run an insulated trip wire from the outside rail by insulating it for about five feet or so. The green light stays on and the red light gets turned on when a train enters that section of track.

Lee Fritz

i am running fastrack by lionel.  i had thought i had isolated the loop from the other one but when i put my meter to it it came up as they both were the same.

Again, what is the purpose of the isolation?  Are you creating multiple power districts, or are you trying to operate signals by isolating the outside rail?

With Fastrack, plastic pins are not an option.  I normally use the Dremel cutoff wheel to slice a rail.  I then fill it in with JB-Weld for a smooth ride.  Note that Fastrack has the two outside rails connected with jumper plates, to isolate the outside rails, you need to remove them from the affected sections.  Fastrack also has the 1 3/8" section that has a jumper to isolate the center rail.

i wanted to do that so i can mKW Multiple power districts so i can turn off part of the line and park a train on that section if i want to put a different train on there.  

For power districts, just isolate the center rail.  Obviously, with Fastrack the easiest way is to incorporate the 1 3/8" section and just pull the jumper.  You can then run a switched power feed to the siding to handle powering it.