So Just What Does "Ambient" mean?


Old 11-19-01, 08:57 PM
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Old 11-17-04, 07:23 PM
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So Just What Does "Ambient" mean?

Table 310.16 gives ampacities for conductors relative to an "ambient" temperature of 30C. Article 310.10 talks about ambient temperature but really just discusses common sense things that impact temperature. I have found no real reference to exactly what "ambient"temperature is, where it is measured or how itis measured, especially as it pertains to wires in conduits. Is it just the general temperature of the environment around the conduit? The temperature of the surface to which the conduit is attached? So temperature inside the conduit?

Any references in the spec to which you can point? Anyone have a notion?

Andrew Volk
Old 11-17-04, 07:39 PM
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Ambient to me always means the surrounding environment. For the most part you don't have to be much concerned with it. However, there are applications where one should consider the effects of elevated temperatures. You see wires that are made to run in hot air ducts where the ambient may be well over 100 degrees. A person may run electrical lines in a steam tunnel where it could be constantly exposed to higher temperatures as well. That's why they make wire designed to function at these higher ambient temperatures. There may also be limits to the number of wires permitted in a conduit when that conduit is installed in a higher than normal ambient environment. Just consider what kind of temperature is likely to be "normal" for the installation that you have in mind and consult the design paperwork and codes to see if the materials you have in mind will function in that environment.
Old 11-17-04, 07:40 PM
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Ambient tempature is basically the tempature of the enviroment the wires are in. In an attic, the ambient tempature may be 120 degrees, in a cold storage warehouse, it could be 25 degrees. Table 310.16 is talking about the ambient tempature as in the tempature of the enviroment the wires or conduit, etc are in. You have to start off with the ambient tempature when derating conductors to find their allowable ampacity. Thats why table 310 15 (b)(2)(a), I believe it is goes even further into telling you to derate the ampacities further depending on how many wires are in a conduit, it deals with the tempature of the wires inside the pipe. Wires do generate heat, and that must be taken into effect. The heat they generate and the surrounding enviroments tempature all play a role in deciding how many amps a wire can carry, as does the conductors size. So as an answer to your question, without the drawn out explanation, yes, it is the general temperature of the environment around the conduit.

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