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Illustrated Changes to the NEC, 2002 Edition - Part 1

Article 310

Conductors for General Wiring

310.15 Ampacities for Conductors

A new exception was added and it reads:

(B) Table 310.16 Ampacity
(2) Adjustment Factors.
(a) More than Three Current-Carrying Conductors in a Raceway or Cable.
Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 24 in. without maintaining spacing, the allowable ampacity of each conductor must be reduced as shown in Table 310.15(B)(2)(a).

Exception No. 5A: The ampacity adjustment factors of Table 310.15(B)(2)(a) do not apply to AC or MC cable without an overall outer jacket under the following conditions:
(a) Each cable has not more than three current-carrying conductors
(b) The conductors are 12 AWG copper
(c) No more than 20 current-carrying conductors are bundled or stacked

Exception No. 5B: When more than 20 current-carrying conductors are bundled or stacked for more than 24 in., an ampacity adjustment factor of 60 percent must be applied.
Intent: The new exception is actually two exceptions, depending on the condition and applies only to 12 AWG AC or MC cable without an outer cover. The first part of the exception allows up to 20 current-carrying conductors (for example ten 2-wire cables or six 3-wire cables) to be bundled without any ampacity adjustment. The second part of the exception permits an ampacity factor of only 60 percent if more than 20 current-carrying conductors (eleven 2-wire or seven 3-wire cables for example) are bundled together longer than 24 in. Figure 310–2

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