Question from Derek <omitted>: I see that your 30A strips have three output branches, but your 60A strips have six branches. Why?
Engineer Reply: The branch circuit protection, as required by the NEC, limits the output branch draw to 20A. If you have only three branches on a North American 208/120V three-phase circuit, you are then limited to roughly 35A maximum on the input lines (20A x 1.732 = 34.64A). So, in order to keep from limiting your 60A circuit to 35A, the optimal thing to do is split those output branches in two. With six branches each protected by 20A fuses or circuit breakers, the entire 60A circuit capacity can be utilized.
It is confusing as it seems that the rated input power does not match the power delivered by some PDU's. Do some manufacturers produce products with branch circuits that do not allow the full power input to be distributed by the PDU?
Posted by: Jospeh Jones | August 11, 2009 at 11:29 AM
Yes, you will find products on the market that utilize 50A connectors but then state that the limit of usage is 35A. This is due to having only three branch circuits protected at 20A each. Since it is required by NEC to protect the branch to 20A, the only way to get to 50A or 60A is to have six branch circuits like Server Technology CDU's.
Posted by: Robert | August 12, 2009 at 06:44 AM