Typically, the industry (combine cycle power plants) I am in utilize Cablebus for connections between the secondary side of large MV and LV transformers and MV and LV switchgear (up to 4000A). NEC 370.4(B) permits the sizing of Cablebus cables based on the free air rating of single conductor cables (Table 310.17,19,69,70). However, once you are land the cables in the switchgear you are limited to 110.14 (C)(1) and the cables are restricted by Table 310.16 (2008) as least on the LV cables (MV cables are not really affected as indicated in 110.40). There are no such temperature limitations at the transformer as these terminations can handle the transformer hi-spot winding temperatures well past the cable insulation rating (120C or higher).
The LV switchgear manufacturers all state their equipment is rated at 75C based on Table 310.16, therefore the use of Cablebus is of no benefit as you can not make use of the free air cable ampacity rating. Of course, the Cablebus manufacturers ensure me there are no issues at the equipment terminations as they have been supplying these designs for years. What gives..who is right?
The LV switchgear manufacturers all state their equipment is rated at 75C based on Table 310.16, therefore the use of Cablebus is of no benefit as you can not make use of the free air cable ampacity rating. Of course, the Cablebus manufacturers ensure me there are no issues at the equipment terminations as they have been supplying these designs for years. What gives..who is right?
