Sizing main OCPD for single phase loads connected to 380

[pablo r. reyes]

Gentlemen,

In a distribution panel with system voltage of 480V-380Y/220V, feeding 3 identical branch circuit loads of 10kVa, distributedly connected to line to ground (220V - Ground). I would like to know, what is the basis for sizing the main OCPD for these loads? Is it 10,000VA/220V = 45.45A? Square root of 3 is not necessary. In my understanding, multiplying factor 1.732 will be used only when the loads are connected to line to line, that is 380V L-L. Here the line current is 1.732 x phase current. But for Line to Ground connection of loads, I think multiplying factor 1.732 is not necessary in order to obtain the line current, because the line current is equal to phase current. Please help me about this.

 

[templdl]

Re: Sizing main OCPD for single phase loads connected to 380

For my perspective is the breaker protecting the loads? Normally you size the cable to serve the loads and then you select a breaker to protect the cable.
Have you sized the cable yet? If a main in a panel, what is the panel ampacity. I assume that if this is a main for a panel that you have sized the panel for the loads to be served.
The I assume that you have selected a transformer of sufficient capacity to serve the loads. You should be looking in the area of 125% of the xfmr FLA. Have you considered reviewing NEC art 450?
Be careful of getting the cart before the horse.

 

[charlie b]

Re: Sizing main OCPD for single phase loads connected to 380

I am closing this thread. It is essentially the same question that is being discussed here.

But I will say that the factor of the square root of three applies to both line-to-line and line-to-neutral configurations.