single conductor/three conductor cable?

[FuzzyQ]

I'm looking at sizing of conductors/cables. My questions are: when you choose single conductor cable and when you are supposed to use three conductor cables? From CEC code Table 1 which is the allowable ampacities for single copper condctors and Table 2: the allowable ampacities for not more than 3 copper coductors I can see that the same size of cable flows diffenrent allowable current.

For Ex.If I have a transformer of 150kVA and the secondary is of 208V 3ph, which means the secondary FLA is about 416A, then by code I should use 1.25x416A=520 to size the conductor. I will end up with 3x1c350kcmil for single conductor cable, and 2x3c250 for three conductor cable.

Plus, how should I pick the proper size of grounding wire coming along with the single conductor cable? Do three copper conductor cables always have grounding wire inside the insulation level or I have to specifically pick the 3+1 type?

Thanks very much for your help.

 

[advidana]

What is the CEC code?

 

[waross]

Table 1 is for single conductors in free air. It is used for wires on poles, spaced single conductor cable in cable trays and other spaced configurations. Note that table 1 is for installations in free air where there is a movement of air to remove the heat generated in the cables.
Table 2 is for three conductors in a conduit, wireway or cable.
It is based on more restricted air flow than table 1. When considering the three conductors, the ground is not counted as a current carrying conductor. The neutral is only counted as a current carrying conductor in a two wire single phase circuit, and three wire circuits derived from two phases and a neutral from a three phase system.
respectfully

 

[waross]

advidana;
Canadian Electric Code up north. It is very similar to the NEC, but there are some significant differences.
respectfully

 

[FuzzyQ]

Thank you waross!

 

[advidana]

thank waross for the info