Small wire derating
- Thread starter 194142
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peter d
Senior Member
- Location
- New England
Re: Small wire derating
Derating factors are located in 310.15(B)(2). (2002)
Derating factors are located in 310.15(B)(2). (2002)
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: Small wire derating
To derate conductors, start with Table 310.16, and based on the type of insulation use the ampacity in that column. Requirements for derating are in various locations besides Table 310.16 which covers temperature variations. 310.15 is more specific.
Secondly the permissible ampacity is not just the derated amount, it is the lesser, in your case, of the derated amount or 240.4(D)
Does that help?
Jim T
To derate conductors, start with Table 310.16, and based on the type of insulation use the ampacity in that column. Requirements for derating are in various locations besides Table 310.16 which covers temperature variations. 310.15 is more specific.
Secondly the permissible ampacity is not just the derated amount, it is the lesser, in your case, of the derated amount or 240.4(D)
Does that help?
Jim T
charlie
Senior Member
- Location
- Indianapolis
Re: Small wire derating
Midget, the ampacity tables are to be reduced by the ambient temperature and where multiple current carrying conductors are bundled together in a raceway or in groups of cables. There are rules for that in 310.15 and at the bottom of the tables. These rules modify the amperes shown in the tables.
Midget, the ampacity tables are to be reduced by the ambient temperature and where multiple current carrying conductors are bundled together in a raceway or in groups of cables. There are rules for that in 310.15 and at the bottom of the tables. These rules modify the amperes shown in the tables.
bphgravity
Senior Member
- Location
- Florida
Re: Small wire derating
Derating is a process of reducing the ampacity of a conductor due to various conditions of the installation. In order to understand how much current an insulated conductor can carrying, one must know several apsects of the installation. Table 310.16 is sortof a staging platform to work from. Read the title of the table. If any of these conditions are different, such as higher temperatures, more current-carrying conductors in a raceway, and other issues such as voltage drop and specific load conditions such as harmonics or continuous loading, it will reduce that amount of current that conductor can carrying without exceeding its insulation temperature rating.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Small wire derating
The mission is to protect the conductor?s insulation system. Too much current, and it will be damaged. Damage could lead to a short circuit, or to a fire. It all comes down to the temperature that is seen by the insulation. Factors that can increase that temperature include the current going through the wire, the ambient temperature (i.e., surrounding the wire), and the presence of other wires nearby (i.e., contributing their heat to the party).
The mission is to protect the conductor?s insulation system. Too much current, and it will be damaged. Damage could lead to a short circuit, or to a fire. It all comes down to the temperature that is seen by the insulation. Factors that can increase that temperature include the current going through the wire, the ambient temperature (i.e., surrounding the wire), and the presence of other wires nearby (i.e., contributing their heat to the party).
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