Cable Size!!!

[Eduardo Maun]

I find sometimes that they used different cable size but the breaker rating is just the same, One factor I think because of the load connected to it.


Ex. 100A they used 4 core x 50 mm square; 100A they used 4 core x 35 mm square, Is temperature a factor?Is there any other factor that affects the cable size?

Or both cable size can handle a 100A? Is it for safety reason why they used 50 mm sq.?

Thank you!!!

 

[haskindm]

I am not familiar with the conductor sizes that you are quoting. The NEC uses AWG and Circular Mils to size conductors. There are many reasons to use different conductor sizes than the breaker would indicate. One is a motor load where the breaker is sized at a minimum of 250% of the FLC of the motor. Another would be increased conductor size to compensate for voltage drop. Conductor size may also be increased to compensate for high ambient temperature or for a large number of conductors being installed in a raceway. Spend some time studying article 300 of the NEC, there is a great deal more to sizing conductors than the amperage of the circuit breaker.

 

[kc8dxx]

Looking for my copy of the Euro standard ...

 

[kc8dxx]

EN60204-1:1997 paragraph 13 and appendix C describe wire ampacity ratings and overcurrent protective device sizing. I am assuming that by 4 core you mean 3 conductors plus ground. 50mm wire has an unadjusted ampacity of 123A, 35mm wire has an unadjusted ampacity of 104 to 114A, depending on the installation method. My guess is that the reason you see different wires installed for the same breaker is that an installer choose to derate one setup, and another installer choose not to derate the other setup.