Appendix ANNEX O EARTH PROTECTION OF THE VEHICLES' METAL PARTS

All the metal parts of the vehicle:

• likely to be touched by persons, or possibly by animals, and at risk of becoming a source of excessive contact voltages, as the result of a fault in the vehicles electrical installation or because of parts of the catenary becoming detached, or

• an accident risk as a result of the arcing of switch-gear subjected to high currents in the presence of dangerous materials,

shall be set at the same potential as the rail through connections offering the lowest possible resistance.

Electric resistance between metal parts and the rail for a two-axle vehicle shall be less than or equal to 0,05 Ohm. This value is measured with a constant sustained current of 50 amps and a voltage equal or lower than 50 volts.

The metal parts in the roof must be bonded to all conductive elements inside the vehicle, where they might be accessible, and must be bonded to the body of the vehicle in a safe way.

All the electrical installations and are connected to the main power circuit, and have metal parts which are likely to be touched and are not switched under power must have their metal components bonded with the mass of the vehicle in a safe way.

All the metal parts of a vehicle (other than those covered in the previous point) which are susceptible to be touched and, although not switched under power, risk being switched accidentally, shall be bonded in a safe way if the nominal voltage of the part concerned is greater than:

• 50 V direct current

• 24 V alternating current

• 24 V between phases for three phase current where the neutral is not bonded and

• 42 V between phases for three phase current when the neutral is bonded.

The cross-section of earthing bond is a function of current to be conducted; it must be sized so as to guarantee the safe functioning of the circuit breakers if tripped.

Antennae fitted outside vehicles have to fulfil the following conditions:

• the conductive parts of the antenna must be fully protected from catenary voltages by a protective device immune to impacts,

• the antenna system has to provide be provided with a single point earth connection (antenna with static earthing),

• an antenna fitted outside the vehicle that does not respond to the previous conditions must be isolated, by means of high voltage capacitors connected to other over-voltage devices, connected to the inside of the vehicle.