Principal Engineer at AES specializing in medium voltage Distribution overhead and underground
There are some common things that aren’t considered by those outside of the Underground Electric Utility profession when it comes to manhole and duct systems for Distribution. This is especially true if the infrastructure is in a congested urban environment. This could be professionals in other industries, Town/City officials and even sometimes employees in the industry who are only exposed to Overhead infrastructure. This is just a few: “You can lay the duct bank right on top of the _______” On top of the 60-year-old water main? On top of the Natural gas line? There are accepted clearances between infrastructure. Clearances are maintained for many reasons. Some of which include avoiding damage to the other party’s infrastructure, access for maintenance/upgrades, future expansion, demarcation between facilities and of course safety. There are exceptions but the decision to reduce clearances need to be carefully weighed and all parties involved need to agree. “If the manhole and duct system fits in the selected path then all is good.” We can't just pick an available path down "Main Street" with no regard to distance and bending radii from point A to point B and call it good. We are not transporting a fluid like water or natural gas (at least on purpose…). Conduit in the electric system provides the path for the electric cable to be pulled through. The path will affect pulling forces and sidewall pressures exerted on the cable during the cable pulling process. If these forces aren't kept below certain thresholds, then the cable can be damaged enough to reduce its life or in extreme circumstances get stuck in the conduit (not emerge from the other end) or break completely. “If the pulling crew can get the cable pulled through the conduit, then the cable will work.” This is related to the always problematic, "I can get it through the pipe" statement from the cable pulling crew. Forcing the cable can cause damage. If it doesn’t get stuck or break, there can still be damage that will probably show up when tested or energized. If it isn’t immediately obvious because the breakers fail to close permanently then the damage may reduce the life of the cable. It may not fail tomorrow or next week, but it will fail prematurely. Do you have any????
