![]() ![]() There is another old construction industry axiom: Even if there are substantial cost savings, the contractor will get most of it if you have to execute a change order.Īlso, I agree with Mark that use of EPR would be much preferred over standard XLPE in this short run of cable. If you have already bid this project, then the contractor's agenda is not the same as yours. This is a good compromise and is an engineered product. If you don't want to use rigid bus, consider use of cable bus such as manufactured by Calvert. Also, for an underground installation, the ampacity of each conductor must be de-rated to account for the mutual heating in the duct bank. You don' mention the voltage, but assuming it is 15 kv class, there will be MANY conductors per phase in a cable installation. Bus Duct RajT (Electrical) 7 Jan 03 08:35ĭoes this have to be underground? I would think an above-ground installation, perhaps using cable tray would be preferable, everything else being equal. Since when in this business can we predict something better that within 5%? Not that often. The cable ampacity calculations have enough slop in them the way it is. 5 conduits run in parallel for 100' will make the cable within 5% of each other or less. EPR can handle higher temperatures which is what usually drives the current handling limitations in a duct bank.ĭon't worry about getting the cables "exactly the same length" in a duct bank. ![]() Moisture is bad news for it, even if you "keep it dry". XLPE cable by itself is generally not a long-lived cable in medium voltage applications. Repeated bus failures drove us to doing that. ![]() We had several throat-connected 22 MVA transformers that we had to convert over to air-insulated bus, not a pretty project. Generally in an outdoor application bus duct doesn't like getting dirty, but you can't get it out of service to clean it. I've had very poor experience with 15 kV class bus duct. Bus Duct cuky2000 (Electrical) 6 Jan 03 13:27 Lastly, I am a professional engineer who work for many contractors in the past (40 years in electrical designe, construction and maintenance) and I would suspect the cable substitution is most likey driven by economics.įamous last words in the construction business "you get what you inspect not what you expect" RE: XLPE Cable vs. This will enable you to install a replacement cable in the event of a cable or termination failure. I would recomend that if you go with the conduit/wire have the contractor install at least two full size spare conduits with a pull rope. One issue with cables is maintainig conductor lengths. Using cables (underground encased in concrete) to connect the two units would eliminate the entry problem. If it is outdoors then the bus connection require special attention (avoid entering the top due to water sealing problems, there will be problems in time). This is usually done on units that are close to each other. Not knowing more about the specifics (size, distances, voltages, etc.) I would prefer the bus connection. ![]()
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