malachi constant
Senior Member
- Location
- Minneapolis
Two questions, somewhat related:
1. When performing an arc flash study you often have pieces of equipment that get calculated at multiple points on the equipment (for example a transformer at both primary & secondary, ATS at em/normal/load). Often the different points yield different PPE categories. I assume it is best practices to put one single label on the equipment that reflects the worst case scenario. Thoughts?
2A. The way we typically model our switchboards in SKM is: incoming feeder -> main CB -> direct to switchboard bus. This yields a calculation at the switchboard bus (on the load side of the main CB) but not on the line side of the main CB. I have tried adding in a bus in between the incoming feeder and main CB, but the program won't let you - I believe because it requires a wire be added somewhere in between the buses. In real life wouldn't opening up the first of the switchboard expose you to a potentially worse arc flash on the line side of the main? Shouldn't it be critical to get a calculation at that point? What should I do - add a one-foot section of bus or something?
2B. We typically treat our switchboards in SKM as one point. Should we be taking into account the length of the bus, and treat it as a cable busway instead of a single point? I am not aware of anyone doing this as a standard practice for arc flash calculations, but curious as to the community's thoughts.
Thanks!
1. When performing an arc flash study you often have pieces of equipment that get calculated at multiple points on the equipment (for example a transformer at both primary & secondary, ATS at em/normal/load). Often the different points yield different PPE categories. I assume it is best practices to put one single label on the equipment that reflects the worst case scenario. Thoughts?
2A. The way we typically model our switchboards in SKM is: incoming feeder -> main CB -> direct to switchboard bus. This yields a calculation at the switchboard bus (on the load side of the main CB) but not on the line side of the main CB. I have tried adding in a bus in between the incoming feeder and main CB, but the program won't let you - I believe because it requires a wire be added somewhere in between the buses. In real life wouldn't opening up the first of the switchboard expose you to a potentially worse arc flash on the line side of the main? Shouldn't it be critical to get a calculation at that point? What should I do - add a one-foot section of bus or something?
2B. We typically treat our switchboards in SKM as one point. Should we be taking into account the length of the bus, and treat it as a cable busway instead of a single point? I am not aware of anyone doing this as a standard practice for arc flash calculations, but curious as to the community's thoughts.
Thanks!