ces
Member
- Location
- Northern California, USA
We have an existing 800A feeder (2) 4"C EMT 3 500kCM & 1#6G all CU paralleled 2 per phase and ground on the secondary of a 225kVA transformer 480-120/208Y. There is 400A CB on the primary and an 800A CB downstream, but obviously the issue is an undersized ground wire. My firm is responsible for recommending a solution to this.
My initial response was that the ground wire needed to be at least 1/0 per 110.122, to pull out the #6 and install the 1/O. Someone else on my team suggested that the ground was not required as the metallic conduit could act as a ground. We agreed this was true per code provided the conduit was installed with appropriate grounding bushings and jumpers. I added that this was not a good idea as this was a large datacenter where as far as we knew every other conduit had a ground wire providing the ground path - my thinking was that someone working on the system would not expect the conduit to be the ground path, especially when there was a green insulated wire present, which I argued would be misleading and therefore unsafe. And I added that if the conduit were to be the path the #6 wire should be removed or at least be disconnected and taped off, for example with black tape.
And that was the formal recommendation we made, with some disagreement in-house remaining as to whether the #6 ground could remain. My question is is there anything in code that allows the #6 green insulated wire to remain when the ground path is (verified to be) the metallic conduit?
All comments appreciated ... on this particular (and all) matters I would like to be right about my point of view! I relate to it like in a fire alarm system where you cannot have a device like a smoke or a pull station or any other device that does not work as it is supposed to.
My initial response was that the ground wire needed to be at least 1/0 per 110.122, to pull out the #6 and install the 1/O. Someone else on my team suggested that the ground was not required as the metallic conduit could act as a ground. We agreed this was true per code provided the conduit was installed with appropriate grounding bushings and jumpers. I added that this was not a good idea as this was a large datacenter where as far as we knew every other conduit had a ground wire providing the ground path - my thinking was that someone working on the system would not expect the conduit to be the ground path, especially when there was a green insulated wire present, which I argued would be misleading and therefore unsafe. And I added that if the conduit were to be the path the #6 wire should be removed or at least be disconnected and taped off, for example with black tape.
And that was the formal recommendation we made, with some disagreement in-house remaining as to whether the #6 ground could remain. My question is is there anything in code that allows the #6 green insulated wire to remain when the ground path is (verified to be) the metallic conduit?
All comments appreciated ... on this particular (and all) matters I would like to be right about my point of view! I relate to it like in a fire alarm system where you cannot have a device like a smoke or a pull station or any other device that does not work as it is supposed to.