49 CFR §238.425

1. (a)Circuit protection.
   1. (1)The main propulsion power line shall be protected with a lightning arrestor, automatic circuit breaker, and overload relay. The lightning arrestor shall be run by the most direct path possible to ground with a connection to ground of not less than No. 6 AWG. These overload protection devices shall be housed in an enclosure designed specifically for that purpose with the arc chute vented directly to outside air.
   2. (2)Head end power, including trainline power distribution, shall be provided with both overload and ground fault protection.
   3. (3)Circuits used for purposes other than propelling the equipment shall be connected to their power source through circuit breakers or equivalent current-limiting devices.
   4. (4)Each auxiliary circuit shall be provided with a circuit breaker located as near as practical to the point of connection to the source of power for that circuit; however, such protection may be omitted from circuits controlling safety-critical devices.
2. (b)Main battery system.
   1. (1)The main batteries shall be isolated from the cab and passenger seating areas by a non-combustible barrier.
   2. (2)Battery chargers shall be designed to protect against overcharging.
   3. (3)Battery circuits shall include an emergency battery cut-off switch to completely disconnect the energy stored in the batteries from the load.
   4. (4)If batteries are of the type to potentially vent explosive gases, the batteries shall be adequately ventilated to prevent accumulation of explosive concentrations of these gases.
3. (c)Power dissipation resistors.
   1. (1)Power dissipating resistors shall be adequately ventilated to prevent overheating under worst-case operating conditions.
   2. (2)Power dissipation grids shall be designed and installed with sufficient isolation to prevent combustion between resistor elements and combustible material.
   3. (3)Power dissipation resistor circuits shall incorporate warning or protective devices for low ventilation air flow, over-temperature, and short circuit failures.
   4. (4)Resistor elements shall be electrically insulated from resistor frames, and the frames shall be electrically insulated from the supports that hold them.
4. (d)Electromagnetic interference and compatibility.
   1. (1)The operating railroad shall ensure electromagnetic compatibility of the safety-critical equipment systems with their environment. Electromagnetic compatibility can be achieved through equipment design or changes to the operating environment.
   2. (2)The electronic equipment shall not produce electrical noise that interferes with trainline control and communications or with wayside signaling systems.
   3. (3)To contain electromagnetic interference emissions, suppression of transients shall be at the source wherever possible.
   4. (4)Electrical and electronic systems of equipment shall be capable of operation in the presence of external electromagnetic noise sources.
   5. (5)All electronic equipment shall be self-protected from damage or improper operation, or both, due to high voltage transients and long-term over-voltage or under-voltage conditions.