While working on a set of plans that will bond our existing traffic signal structures in accordance with NEC requirements, I have come across a question that I could use some advice on. The majority of our traffic signal systems have their own separate services, some with external service disconnects and some without. Our statewide specifications now require the use of a bonding conductor connected to each metallic structure (handhole, signal post, mast arm asembly, etc.) to provide an effective ground-fault current path in the event of a fault. In most cases, this involves the installation of a #6 conductor from the electrical service (either the external disconnect if present or to the power terminal strip in the equipment cabinet where the neutral wire is bonded to the ground wire. Each metallic structure is then connected to this "system ground" through the means of a mechanical connection.
However, in one of our downtown systems, the traffic signal installations have their own separate services (usually 120V or 240V), but the luminaires that are mounted to the combination mast arms are connected to the city's lighting system which is fed from a separate 277V service(s). The mast arm poles are already bonded to the 277V lighting system. Would it be acceptable to ground the traffic signal handholes and remaining signal posts using the ground wire from the 277V lighting system or should we install a separate ground wire from our service disconnect or controller cabinet power panel to ensure a low-impedance ground-fault current path? If the lighting ground conductor is coupled to the traffic signal ground conductor, then I would think that this would suffice to provide a low-impedance ground path.
I have asked several of our electrical contractors, and the answers vary, so I would appreciate any information that can be provided on this.
However, in one of our downtown systems, the traffic signal installations have their own separate services (usually 120V or 240V), but the luminaires that are mounted to the combination mast arms are connected to the city's lighting system which is fed from a separate 277V service(s). The mast arm poles are already bonded to the 277V lighting system. Would it be acceptable to ground the traffic signal handholes and remaining signal posts using the ground wire from the 277V lighting system or should we install a separate ground wire from our service disconnect or controller cabinet power panel to ensure a low-impedance ground-fault current path? If the lighting ground conductor is coupled to the traffic signal ground conductor, then I would think that this would suffice to provide a low-impedance ground path.
I have asked several of our electrical contractors, and the answers vary, so I would appreciate any information that can be provided on this.
