Cable sizing of a power feeder
Cable sizing of a power feeder
(OP)
Incase of a cable feeding power from one switch-gear to another one, I understand that the cable better shall be sized as per the least of outgoing breaker of later and incoming breaker of the second one. But sizing as per the connected load on the downstream swgr is not a good practice as we are trying to size on some thing which can change.
Now, Can any one suggest if any standard (IEC / ANSI) requires to be done this way or is it just a good practice followed?
Thanks in advance
Now, Can any one suggest if any standard (IEC / ANSI) requires to be done this way or is it just a good practice followed?
Thanks in advance






RE: Cable sizing of a power feeder
RE: Cable sizing of a power feeder
RE: Cable sizing of a power feeder
RE: Cable sizing of a power feeder
NEC [NFPA 70] art. 240.4 Protection of Conductors (B) up to 800 A and (C) for above states:
(B) “The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used”[ if the next higher is less than 800 A.]
(C) “Where the overcurrent device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device”
RE: Cable sizing of a power feeder
Now you have a good operating load and you can select a suitable breaker AF/AT rating both in the source and destination Switchgear. Based on the upstream breaker trip setting, the cable needs to be selected. If the Switchgears are far apart, a voltage drop calculation is required, usually limiting the drop to 3%. A check should be done to see that the selected cable can be terminated on the breakers / terminating points.