NEC: NFPA 70 Standard


NEC: NFPA 70 Standard

The National Electrical Code (NEC) standard uses the NFPA 70 method and applies to above ground cables.

Tray Configuration Options

This method does not consider fill conditions exceeding the nominal depths of a maximum fill condition.

  • Top Covered tray
  • Cables kept with Maintained Spacing

Cable Raceway Installations

  • A/G Conduit
  • A/G Trays
  • Air Drop
NEC NFPA70 Cable Raceway Installation Types

Alert for Allowable Ampacity

ETAP provides alerts to the user when a critical situation occurs. A critical situation may deteriorate

the cable and tremendously reduce its lifetime. The alerts tool of the cable ampacity study software is based on the options listed below.

  • Based on the calculated Derated Ampacity
  • User-Defined value
  • Based on thermal analysis results of underground raceway systems module

Temperature Correction

Calculate the derated ampacity based on the ambient and conductor temperatures. In addition, the user can either select the base temperature provided by the manufacturer or the operating temperature of the cable.

Cable Fire Protection

Select from fire protection layers available in the ETAP Library:

  • Cable Thermal Insulation
  • Cable Insulation Length of able thermal insulation

This cable ampacity analysis program calculates derating factors for cable trays according to NEC. The cable ampacity analysis software applies to cables in above ground trays, conduits, and air drop.

The NEC Standard does not provide cable ampacity derating due to bottom cover or correction of the cable ampacity multiplying factors due to the cumulative effects of combinations of tray covers and fireproofing. In general, cable sizes of 2/0 AWG and smaller are installed in cable trays in a randomly filled manner, with a maximum of two cables high.

Base cable ampacity of randomly filled trays are based on installations at a uniform depth up to the maximum of 30% fill for 3 or 4-inch tray depths. The cable ampacity assessment tool applied here corresponds to a maximum fill condition and does not consider fill conditions exceeding the nominal depths.

For NEC standard, the selected cable Base ampacity must be in accordance with the cable ampacities listed in the tables from NEC Article 310.



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