FloydF
New User
- Location
- Jacksonville FL
- Occupation
- Engineer
I have searched the forum, but have not found a similar question. We have a concrete cable stay bridge that is having the electrical system replaced. Going out to each bridge pier, there are 240/480 volt single phase circuits from a utility service. At each pier, there is a transformer mounted outside on a wall (accessed by standing on a metal platform over the water) that will step the voltage down to 120/240V and serve some of the loads. The location is several hundred feet above water at the roadway level, and a half mile from the service entrance. At the top of each pier (several hundred feet above) are two stainless steel bars that were connected to the bridge steel (so the steel is "exposed") when the bridge was built. However, we have air terminals protecting the tower and they are connected to ONE of the steel bars. For the transformer, I think that we need the separately derived system to have a grounding electrode and I planned to connect to the other steel bar (which is admittedly close to the bar being used for the air terminals ground) and use the bridge steel. BUT, that does create the concern of a lightning strike also putting a surge on the transformer and damaging equipment. The Contractor feels that the NEC states that the grounding should be done "at the main grounding connection and not at a subpanel or transformer". He thinks that it might create a parallel ground path and increase the chance of damage to the equipment. In a similar situation on a different bridge, they have transformers that they connected to the same ground as the air terminals but they also connected to the ground conductor going back to land. I believe that might be a code violation. And, I do not see the value of installing a ground conductor several hundred feet into the water and the rod being mounted to the side of the same bridge pier, versus using the steel of the pier going into the water. Any thoughts?
