Table 1 NEC 2014

[Rob_Ram77]

Hi everyone, on table 1 on the NEC, if I use 2 conductors I can only use 31% of cross section of the conduit, buy if I use over 2 conductors that percentage jumps to 40%, why is that?

 

[Carultch]

Hi everyone, on table 1 on the NEC, if I use 2 conductors I can only use 31% of cross section of the conduit, buy if I use over 2 conductors that percentage jumps to 40%, why is that?

In general, the conduit fills are set up so that it represents between 70% to 80% of the conduit diameter.

A round wire in a round raceway at 53%. sqrt(0.53) = 73%

If you pack two circles together, they will take up an extra long oval shape. If you pack the conductors wall-to-wall so that the entire diameter is filled, the most you can fill the conduit is 50% by area. 31% is the reduced fill percentage, which will fill it at about 78% of the conduit diameter.

But if you pack more than two circles together, the more you pack, the more circular that overall shape becomes. Initially triangular for three wires, then square, then pentagonal, and hexagonal. Your packing becomes more efficient by area than it is for two circles in a circle.

 

[GoldDigger]

Another factor is looking at what happens when you pull through a bend. Two wires which come close to spanning the entire diameter will jam (wedge) very hard in that situation and be unpullable.

Sent from my XT1585 using Tapatalk

 

[iwire]

Hi everyone, on table 1 on the NEC, if I use 2 conductors I can only use 31% of cross section of the conduit, buy if I use over 2 conductors that percentage jumps to 40%, why is that?

Two conductors in a raceway tends to jam in the corners more than 3 or more conductors do.