First I like to say Hi to all. I love reading the info and stuff here at Hobby Talk. Now to the question. I am run a Atheren's slot car power supply (I picked up at a hobby shop). It puts out 12 volts 1.2 amps. I have the new Tomy terminal so I have one power supply for each lane. Do I need a fuse between the power supply to each lane to protect power supply , cars, track and controllers? If so, should it be a 12 volt 1 amp fuse? Any info would be good. Thanks

The only thing that is really at risk with a low current power supply supply like that is the power supply itself. Worst case, something shorts the rails at full throttle. Check the specification sheet for the power supply to see if it has short circuit protection. If it does not have short circuit protection, or if you want to be extra safe, then put a fuse inline with the positive lead coming from the power supply. The fuse should be sized to the peak current rating of the power supply. If your power supply has a peak current of 1.2A then use a fuse of that rating or slightly lower, like 1.0A.

Higher current power supplies should use a fuse on the positive lead even if the power supply has short circuit protection. Some power supplies react to short circuits by popping an internal breaker or fuse on the power supply itself. Others, notably the less expensive ones, clamp the current to the max level when there is a short circuit. While running most power supplies at max current for extended periods of time can damage the supply, the main concern is that something else in the electrical circuit that has the short will eventually succumb to the high current and overheat, melt, or catch fire. Every circuit is technically fused. Putting a fuse in the circuit allows you to decide which component will be destroyed (or tripped) by the overcurrent situation. This situation is very apparent with battery powered tracks. A car or marine battery can turn just about any conductor, semiconductor, or human body part into a fuse.

In addition to fusing the main positive lead coming from the power supply you can also put fuses or circuit breakers on each drivers station. These fuses/breakers limit the max current that any one lane can draw without disabling power to the whole track. The most common cause of overcurrent in a single lane is hooking up a controller wrong. Shorted rails in a single lane can also cause an overcurrent in one lane. The fuses/breakers used for individual lane protection should be rated less than the main fuse. For high current power supplies that are 10A or greater I use a low voltage DC circuit breaker that is rated at 5A or 7A in each lane in addition to the main fuse. In the case of the 1.2A power supply I would not bother placing fuses or breakers on each lane, just on the main line.

Thanks for the help. I know that the power pack doesn't have circuit protection.

Protect your investment. Fuses/circuit breakers are a form of insurance, if you have it, you probably won't need it (hopefully), BUT if you don't, you'd wished you did! The small investment IS WELL WORTH IT!!!

Fuses from State Farm or Allstate are industry standard, while fuses from Gieco or Progressive are still proving themselves. Go with what you know.