Protection of model railroad electrical circuits:
In modern electrical control design there are several considerations:
1. For devices such as motors etc. the intent is to protect the device itself from overheating, fire or self-destruction. In this instance a circuit breaker is designed to "open" when the normal running amperage is exceeded.
2. For systems involving wiring such as in a home or office the intent is to protect the wiring itself from "overheating" and causing a fire. In this instance a circuit breaker is designed to "open" when the normal design maximum amperage of the wire is exceeded. Local and national electrical codes would apply here. Generally speaking household wiring is designed for a maximum of 20 to 30 amperes with some exceptions such as hot water heaters, ranges, and airconditioners.
3. For model railroad power systems the manufacturer of the power supply or transformer needs to ensure that the device itself does not overheat or self destruct. In this instance a circuit breaker is designed to "open" when the normal design maximum amperage of the transformer is exceeded.
4. For model railroad wiring systems one of the main considerations is to limit arcing and potential overheating of the track and wiring in case of a short due to a derailment. In this instance separate circuit breakers could be used for "each" feeder wiring.
5. For model railroad control systems such as the MTH TIU and AIU units for instance there is often a need to limit the current so as not to exceed the manufacturers maximum rating for internal relays and electronic circuits. In this instance the circuit breaker would be sized to limit the current "load" for these devices. In many cases the manufacturer specifies the maximum rated current (but not always).
In my model railroad power system I protect each circuit by a combination of circuit breakers and fuses (sometimes both) to ensure there are no "burnouts" or otherwise permanent damage to the power system, trains or accessories. For example I use a fuse for control power for turnouts. In this instance I want to prevent the device (turnout solenoid) from self-destructing.
1. For my system I also limit the maximum current for each turnout solenoid by using series resistors. The system is designed to provide only the current needed to activate the device.
2. Since I sometimes operate several turnouts at the same time I will also provide fuse protection in case more than one solenoid fails.
3. I also avoid damage to expensive control components by preventing the possibility of high current overloads through these devices. For example I use separate heavy duty control relays for turnout control and power feeds to the track.
An example of a separate control relay board is shown in the attachment. Even though I use an MTH AIU for remote control the current through the internal relays and circuits within the AIU is maintained less than about 1/2 ampere maximum. I can easily replace the external relays if one fails which minimizes the possible downtime.
Note: Each relay shown plugs into a prewired socket. A change out of a relay can be accomplished in about 1 minute without disturbing the wiring.
