Secondary feeder Sizing conductor from transformer

[Jpflex]

Business want me to upsize to a 500 KVA delta delta 4800 volt primary to 480 volt secondary

This secondary supply Feeder size was calculated at 505.35 amperes based on 1.25% of largest FLA motor plus 100% of FLA if remaining motors

Boss wants to use 4/0 conductor thinking he can split 500 amperes between legs of transformer each around 250 amperes (not paralleling) to motor loads

Doesn’t legs on delta need to be rated for 500 amperes each? Since same current is total on both legs push and pull per phase?

Thanks

 

[Jpflex]

Also I calculated feeder OCPD at 700 amperes based on

The largest OCPD ampacity plus the sum of the remaining FLC amperes of the remaining motors then multiplying figure at 300% for non time delay fuse at 700 amperes next lower standard size fuse for feeders from initial 722.35 ampere total load

 

[augie47]

Difficult to confirm without details but if you have a 3 phase load of 500 amps that would require conductors rated at 500 amps on each phase.

 

[Jpflex]

Difficult to confirm without details but if you have a 3 phase load of 500 amps that would require conductors rated at 500 amps on each phase.

In other words line 1 would need to be rated for 500 amperes and line 2 at 500 amperes as well as 500 amperes so 4/0 conductor won’t suffice?

 

[jim dungar]

Also I calculated feeder OCPD at 700 amperes based on

The largest OCPD ampacity plus the sum of the remaining FLC amperes of the remaining motors then multiplying figure at 300% for non time delay fuse at 700 amperes next lower standard size fuse for feeders from initial 722.35 ampere total load

Conductors are typically sized based on their loading. OCPD are chosen based on selected conductors.

Why are you using non time delay fuses?

 

[Jpflex]

Conductors are typically sized based on their loading. OCPD are chosen based on selected conductors.

Why are you using non time delay fuses?

No pres fete next just option in nec

 

[Jpflex]

Here’s pic of what I propose

 

[jim dungar]

No pres fete next just option in nec

For the most part, commonly available fuses will be time-delay.

 

[Jpflex]

For the most part, commonly available fuses will be time-delay.

Not sure how many seconds of delay is standard needed

 

[jim dungar]

Not sure how many seconds of delay is standard needed

Needed for what?

My basic rule of thumb has been.
just past 6x FLA for 20sec (allows for motor inrush)
12x FLC for 1sec (common for transformer primaries)