![]() ![]() At 13.8kV on the X side of the GSU's, that's 1,673.5 amperes/phase full load capability. The new installation I've gotten involved with in the field has two (2) smaller GSU xfmrs with an ONAF rating of 40 MVA each. Honestly, my question was from the perspective of someone else who I'm likely going to be having a disagreement with. Thanks for any help and guidance on this. In this case, would the ampacity for these cables now be taken from the “Three Circuits” section of Table 310.60(C)(77) or does the Code still consider this a “Six Circuit” installation? How does this get evaluated with regard to Table 310.60(C)(77)? It’s understood the ductbank is still six (6) electrical ducts in a 2Hx3W arrangement but now only one set of cables in three (3) of the ducts is flowing current and giving off heat. In this scenario and with the configuration of the plant, the remaining xfmr will carry the full load and the other xfmr primary side circuit/cabling will be de-energized and not seeing any current flow. My question is related to the scenario when only one of the xfmrs is energized and loaded with the other one out of service. The “Six Circuits” section shows a lower ampacity than the “Three Circuits” section which make sense because there’s a further derating required because of the impact of the extra heat from the cables in the added ducts. When both xfmrs are energized and loaded, it's clear to me that NEC Table 310.60(C)(77) “Six Circuits” section is applicable for determining the ampacity of all the installed cables. One additional important not is that proper spacing of the ducts was not adhered to during the installation. This UG ductbank for both xfmrs for the majority of the run is arranged in a configuration “similar” to detail 3 of NEC Figure 310.60(C)(3) – six (6) electrical ducts in a 2Hx3W arrangement. ![]() Each xfmrs primary side cabling is installed in underground (UG) ductbank and consists of three (3) 15kV, MV-90 rated cables per phase (gauge unimportant for this question). I’m involved with a project that has two (2) large 3 phase xfmrs installed. I have a question related to NEC Table 310.60(C)(77) “Ampacities of Three Single-Insulated Copper Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct) Based on Ambient Earth Temperature of 20☌ (68☏), Electrical Duct Arrangement in Accordance with Figure 310.60(C)(3)." ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |