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Free Guides To Ampacity Adjustments For Wire and Cable
The Copper Development Association announces two new guides for sizing the wires
and cables inside conduits on rooftops in accordance with the 2008 National Electrical
Code (NEC). Available free from CDA, these two publications make it easy to estimate
temperatures inside electrical conduits at various heights above the rooftop
for hundreds of cities across the US and make the necessary ampacity adjustments
required by the Code.
Conduits on rooftop of commercial buildings can be more than 70 degrees Fahrenheit
hotter than surrounding temperatures. For example, depending on the height
of the conduit above the surface of the roof, when the outdoor temperature
reaches
95ºF, the temperature inside the conduit may exceed 165ºF even with no current
passing through the conductors. The 2008 NEC now recognizes that the air
inside conduits on rooftops can be significantly hotter than the surrounding
air. Ampacity
ratings of various wire sizes and types must be adjusted to account for these
elevated temperatures.
The Copper Development Association (CDA) has created a booklet and a slide
tool to assist inspectors, engineers and contractors in making ampacity
adjustments for wire and cable in rooftop conduits.
Hard copies of the booklet titled Derating: Outdoor Temperatures for Various
U.S. Cities and Temperatures Inside Conduits on Rooftops Exposed to
Direct Sunlight are available free-of-charge upon request from CDA. In addition
PDF versions
of the same booklet can be downloaded from www.copper.org.
The slide tool is titled Rooftop Ampacity Adjustments. Hard copies
of the slide tool are available free of charge upon request from
CDA. There
is
no PDF version
of the slide tool.
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