Not aware of codes for low voltage. UL considers anything below 40V as touch safe. So we are left with possible heating of wires.
Make sure that all wire connected to a source (12Volts for example) will not overheat if the maximum possible current is present. This includes the return wires as well. The maximum current is either what your power supply is rated for or what your fuse or breaker (if present) will allow before interrupting the circuit. Active circuit breakers probably don't count as many of them could fail to a short circuit and therefore might no help. At least this is how UL looks at it. You may decide to trust your active circuit breakers anyway. So since we often use small gauge jumpers to connect our bus to the tracks we need to make sure that the circuit is protected to prevent that smaller wire from overheating. So if you use 24 AWG jumpers you should make sure that no more then 3.5 Ampere can flow in the circuit. 22 AWG should be good for 7 Ampere.
Remember that not all short circuits will draw enough current to trip your beakers or your DCC box.
In addition to following the above rule I have my layout power wired to a timer. This way a low level short that might cause local heating cannot persist long term. What if some conductive debris should happen to fall across your buss. It only takes 2 Amperes in a 12 Volt circuit to cause 20 Watts of heating with only 2 Amperes or current. 20 Watts is enough to start a fire.
30 Years experience with product safety and compliance with UL and other regulatory bodies.