Small Transformer Secondary Conductor Sizing

[bozo]

5KVA 480-120/240V single phase transformer feeding a panel with 40A main within 10 ft. of transformer. Does 240.4(D) still apply in this situation, which, assuming the use of 90 deg wire would require #8 AWG instead of #10 AWG? Appreciate any help.

 

[Volta]

5KVA 480-120/240V single phase transformer feeding a panel with 40A main within 10 ft. of transformer. Does 240.4(D) still apply in this situation, which, assuming the use of 90 deg wire would require #8 AWG instead of #10 AWG? Appreciate any help.

Yes, I would think so, # 8 minimum.

 

[Dennis Alwon]

You would not be allowed to use any size conductor at the 90C rating except for derating. So, yes #8 wire would be required for 40 amps.

 

[bozo]

You would not be allowed to use any size conductor at the 90C rating except for derating. So, yes #8 wire would be required for 40 amps.

I forgot about the termination temp requirement. Thanks to all for your help.

 

[cpal]

what is your pri ocp set at?

the 10' within is not an issue if the secondary conductors are installed per 240.21(C) it would need to be total lenght of the seconday conductors.


look at 240.4 (F) see if it fits. Is it a two wire secondary???

 

[Volta]

You would not be allowed to use any size conductor at the 90C rating except for derating. So, yes #8 wire would be required for 40 amps.

Why not? Some terminations are rated for 90 deg C.

 

[Dennis Alwon]

Why not? Some terminations are rated for 90 deg C.

Okay Volta-- You are correct but how many have you seen where both ends are 90c. In fact how many with one end. You know where I am coming from. It is a rare situation where one can use a 90C termination.

 

[bozo]

what is your pri ocp set at?

the 10' within is not an issue if the secondary conductors are installed per 240.21(C) it would need to be total lenght of the seconday conductors.


look at 240.4 (F) see if it fits. Is it a two wire secondary???

It's 3-wire single phase secondary so doesn't fit 240.4 (F)