Hi all,
We have a piece of industrial equipment that is being supplied 200A, 480V 3φ + Ground through a 4-pole power bus (similar to Vahle or Conductix). However, while digging through the drawings, I realized that the machine has some line-to-neutral loads (lighting, cooling fans, power supplies, contactors, etc.). Their neutral bus in the cabinet is being bonded to the ground bus, which is where our supply is connecting. That means that the grounding conductor is carrying current on a regular basis.
The machine is from a European company, and I believe that the codes over there (IEC60204?) permit a combined neutral and ground (PEN or PE-N) in a TN-C type grounding system. However, everything that I'm finding in the NEC and NFPA 79 leads me to believe that is not permitted here in the USA. I'm told that a few years ago someone at our company did an evaluation and said this was ok, but no-one remembers what the justification was.
Do any of you know of any exceptions / sections in the NEC that would permit this? For future machines, we're going to change it to be 3φ + N + Gnd. However, I am concerned about the existing machinery and if we need to do a retrofit with the correct supply.
We have a piece of industrial equipment that is being supplied 200A, 480V 3φ + Ground through a 4-pole power bus (similar to Vahle or Conductix). However, while digging through the drawings, I realized that the machine has some line-to-neutral loads (lighting, cooling fans, power supplies, contactors, etc.). Their neutral bus in the cabinet is being bonded to the ground bus, which is where our supply is connecting. That means that the grounding conductor is carrying current on a regular basis.
The machine is from a European company, and I believe that the codes over there (IEC60204?) permit a combined neutral and ground (PEN or PE-N) in a TN-C type grounding system. However, everything that I'm finding in the NEC and NFPA 79 leads me to believe that is not permitted here in the USA. I'm told that a few years ago someone at our company did an evaluation and said this was ok, but no-one remembers what the justification was.
Do any of you know of any exceptions / sections in the NEC that would permit this? For future machines, we're going to change it to be 3φ + N + Gnd. However, I am concerned about the existing machinery and if we need to do a retrofit with the correct supply.