How many Live Ends do I need for a 30' run of track?

The number of live ends required depends on the load, and not on the length.  The track is able to accommodate 20 Amp, at 80% capacity, i.e. 16 Amp.  That works out to 1920 watts maximum. Say, you are putting (30) LHT-180L-WT (75W) fixtures into the 30' of track.

- Watts/ Volts  = Amps
- Each 75W fixture will draw 75/120  =  0.625 Amps
- (30) 75W fixture will draw 0.625 X 30  =  18.75 Amps
Since the maximum load of the track is 16A, you will need 2 power feeds for 18.75Amp.