Lucent Technologies Lineage
®
2000 ECS Battery Plant J85500D-3
Issue 5 January 1999 Engineering, Planning and Ordering 3 - 13
determining factors in sizing conductors. In systems, such as ac
distribution, with relatively high voltage and low current,
ampacity usually determines minimum conductor size. All
conductors, however, must be large enough to safely carry the
intended current.
Allowable ampacity is provided in Article 310 of the NEC
(National Electrical Code), and it is a function of the following:
• wire size,
• ambient temperature,
• type of insulation, and
• proximity to other conductors.
The ampacity tables are given in the National Electrical Code
(NEC), starting with Table 310-16. These tables, together with
the appropriate notes, determine the current that will result in the
maximum allowable operating temperature for each wiring
method For instance, for the maximum temperature for Type
RHW wire is 75°C (167°F). The current that will result in that
temperature (i.e. the ampacity) is less when the ambient air
temperature is higher and also when conductors are bundled or
side-by-side.
Overcurrent
protection
The rating of an overcurrent protection device (fuse or circuit
breaker) should not exceed the ampacity of the conductor it is
intended to protect. The absolute maximum rating permitted by
the NEC for an overcurrent protector is the next larger standard
rating above the ampacity.
Overcurrent protectors may be sized smaller than this maximum
rating. In general, however, protectors should be rated as high as
allowable to avoid nuisance tripping due to high load conditions
or inrush during start-up.
General
guidelines:
The peak current drain (List 2) is used to size the circuit
protection for each individual load. The fuse or circuit breaker
must also protect the wire connecting to it in accordance with
NEC and local code regulations.
Fuses: Load fuses are not provided with the fuse panels that are
supplied with the ECS power plant. The individual fuse size
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