Most of my electrical work is centered around the elevator industry. I recently had an inspector question the isolation transformers used on an elevator install. Typical elevator install requires a 3 phase step up isolation transformer. The higher voltage is fed into a 12 pulse SCR drive which converts ac to a controlled DC voltage which is then fed to a DC elevator motor. According to article 250.30 there needs to be a grounded conductor(Neutral) in the seperatly derived system in order for the requirements of grounding to be met.
Seperatly derived systems require grounding conductors to building steel structures or water mains. The problem I have is the elevator installation is in a concrete building with no structural steel. I cannot run grounding wire to building steel, so I have to run wire 65 floors to water main. I've never had this questioned before and think that this is an error on inspectors part. My transformers is not grounded a neutral conductor, therefore I believe that this seperatly derived system does not apply to me. Does anyone have any insight.
Seperatly derived systems require grounding conductors to building steel structures or water mains. The problem I have is the elevator installation is in a concrete building with no structural steel. I cannot run grounding wire to building steel, so I have to run wire 65 floors to water main. I've never had this questioned before and think that this is an error on inspectors part. My transformers is not grounded a neutral conductor, therefore I believe that this seperatly derived system does not apply to me. Does anyone have any insight.
