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area vs I

area vs I

area vs I

(OP)

Suppose a wire is carrying 3 phase ac current, as you increase the current, by what magnitude must the cross sectional area increase by?

Is this a linear relationship?


Thanks.

RE: area vs I

It depends. If you want to maintain a constant voltage drop, it's a linear relationship as the resistance is inversely proportional to the cross-sectional area. If you want to comply with NEC ampacity (NFPA 70), it's not linear since the integrity of the insulation has to be taken into account as well.

Glenn

RE: area vs I

A wire won't be carrying 3 phase ac current.  It might be carrying ac current, but not 3 phase current; 3 phase in a single conductor is called a bolted fault.

RE: area vs I

If what do you meant is the maximum admissible for one conductor steady state [balanced] current  of three phased cable [maximum admissible or "rated" is the current- in steady state- which will heat the conductor up to maximum admissible insulation temperature-90 oC for XLPE for instance].
This value depends upon many factors as ambient temperature, ambient material -exposed to free air or concealed in conduits, buried in a certain depth in a certain ground and so on.
If two cables are in the same conditions- for small cross section of conductors- the required cross section will grow[lesser a bit] with the square of current ratio.
For instance, if for 1.5 sqr.mm permissible may be 24 A for 2.5 sqr.mm will be only 32A (32/24)^2*1.5= 2.67 sqr.mm
For instance, if for 2.5 sqr.mm permissible may be 32 A for 4 sqr.mm will be only 42A (42/32)^2*2.5= 4.3 sqr.mm
 

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