| Sizing Power Cable for Ampacity |
 = Equals Power Souce's Breaker/Fuse Name Plate Rating that will feed the load. |
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F) PROTECTOR SIZING: 1) Fuses: 1.1 Maximum Demand Current (List II Drain) x 150% = Fuse size 2) Breaker: 2.1 Maximum Demand Current (List II Drain) x 125% = Breaker Size 3) Non-KS Type Circuit
Breaker: 3.1 Maximum Demand Current (List II Drain) x 150% = Circuit Breaker Size G) DC
POWER CABLES: 1) Engineering Fundamentals: 1.1 Primary Power Cables are the cables that run from the Power Plant to the BDCBBs. 1.2 Secondary Power Cables are the cables that run from the BDCBBs to the Equipment. 1.3 Battery Power Cables are the cables, which run from the power plant to the batteries. 1.4 Vertical runs of power cable, which extend more than 3 floors, shall be provided with twenty feet of horizontal cable run out every third floor to alleviate weight buildup. 1.5 MCM = Thousand Circular Mills; KCM = Thousand Circular Mills (also); AWG = American Wire Gauge. 1.6 General Rule: Bending radius = 10 x
(Diameter of cable) 2) Sizing
Power Cables:
2.1 Max Load Current = Amperage (Ampacity):
o
First Determine if the
cable will be able to carry the amperage necessary.
o
If the current through the
cable exceeds the cable’s amperage, the cable will become the fuse.
o
Determining Ampacity:
§
Ampacity of cable must be greater than 1.25 x (Max
Draw)
§
Example:
·
If the BDCBB is breakered out at 600 Amps, but
its max draw is 480A (only 80% of 600A is to be used), The cable must be sized
at 600Amps to avoid the cable becoming the fuse if more than 480A is drawn.
§
BUT, some customers make the Max Load equal to the breaker size knowing
the equipment will never pull that much. The cable should still be sized at
1.25 x Max Draw
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| It must be understood that a current carrying conductor is sized to the amp rating of the circuit breaker/fuse to which it is fed. The breaker is there primarily to protect the current carrying conductor from seeing more current than it is sized to. Next, when sizing conductors you take the full rating of the circuit breaker/fuse. Finally, when sizing current carrying conductors, the code requires section 110.14(1)(a)(b) before selecting any ampacity table temperature column in NEC2011 Table 310.15(B)(16). Please refer to NEC2011 110.14(1)(a)(b) for determining the proper temperature rating column: Any circuits <= 100Amps or #14 Awg <= circuits <= #1 Awg shall use only the conductor 60˚C Table. Any circuits > 100Amps or Circuits > #1Awg shall use only the conductor 75˚C table. |
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| For assistance, please call (610)952-6067 or email mike@mooreu.com |