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If the accepted fill rating is exceeded, then all the cables in the conduit are derated, lowering their acceptable maximum ambient operating temperature. Derating is necessary because multiple conductors carrying full-load power generate heat that may exceed the normal insulation temperature rating. (NEC 310.16)
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This is similar to the preceding, but rated for dry or wet environments and conductor temperatures up to 75 °C (167 °F), [18] and is commonly used in subsurface conduits which may fill with water. A great deal of THWN wire is actually dual-rated, and meets THHN the specification as well, so may be used in wet environments up to 75°C or dry ...
Fill capacity is provided for furniture systems. Fill capacity is provided for perimeter raceways. Design requirements for poke-thru fittings. Access floor heights are adjusted. In-floor systems include underfloor duct and cellular raceways. Pathway fill is provided for cable tray. A discussion of telecommunications diversity has been added.
Power semiconductor devices have a maximum power dissipation rating usually quoted at a case temperature of 25 °C (77 °F). The datasheet for the device also includes a derating curve which indicates how much a device will dissipate without getting damaged at any given case temperature, and this must be taken into account while designing a system.
A conduit system can be made waterproof or submersible. Metal conduit can be used to shield sensitive circuits from electromagnetic interference, and also can prevent emission of such interference from enclosed power cables. Non-metallic conduits resist corrosion and are light-weight, reducing installation labor cost.
Although only 61% of the conductivity of copper by cross-sectional area, its lower density makes it twice as conductive by mass. As aluminum is roughly one-third the cost of copper by weight, the economic advantages are considerable when large conductors are required. The disadvantages of aluminum wiring lie in its mechanical and chemical ...
[1] [2] The other type of flow within a conduit is pipe flow. These two types of flow are similar in many ways but differ in one important respect: open-channel flow has a free surface, whereas pipe flow does not, resulting in flow dominated by gravity but not hydraulic pressure .