eager2learn
Senior Member
- Location
- Mennifee,Ca
what size conductors do i need for a 225kva three phase transformer on the primary side = 480 @ 270 amps - secondary = 208y/120 @ 625 amps - i feel like im doing something wrong
the owner wants to run 200 amps to all three phases on the line side using existing conductors which are 3/0 - on the secondary side he wants to run 2 panels that are rated at 225 amps each. i am aware that on both the primary and secondary side i will also have to add 125% to the ocpd - i guess the real question that i have is, can i run the 200 amps on the 3/0 conductors or do i have to bump them up to 4/0 - as far as the secondary side the owner wants us to run parallels to each panel individually - i hope that makes sense - he also has existing conductors which are 1/0 - i have to total the load but i am more less concerned with how well the transformer will be effeciecnt.
what size conductors do i need for a 225kva three phase transformer on the primary side = 480 @ 270 amps - secondary = 208y/120 @ 625 amps - i feel like im doing something wrong
I have 3/0 feeding the disconnect on the line side of the cartridge fuses which will be rated @ 175 amps - on the secondary side of the fuses feeding the primary side of the x-frmr i have 1/0 - i then have 1/0 also feeding the two seperate panels on the load side of the secondary - the total load between each panel as of right now is expected to be approximately 40 amps - the panels will be utilized for lighting and a few general circuits. the owner just bought this factory and is trying to utilize all materials with in at no additional expense.
Sounds like to me your conductors are all undersized to begin with. Why don't you size the conductors according to the rated current and set your OCPD according to NEC table 450.3(B).
so if have a 3 - 200 amp fuses at the switchgear which feeds the primary disconnect with the 3/0 conductors which are rated at 225 amps, can these conductors feed the disconnect which will have another set of 3 - 200 amp fuses installed with 3/0 conductors feeding the primary side of the transformer be suitable.
in addition, the two panels located on the secondary side of the transformer are within 7 feet of the transformer, so there is no need for a secondary disconnect. the 1/0 is rated at 170 amps at the total load for both panels is approximately 80 amps, can these conductors be utilized or do i have to also provide 3/0 to both panels.
the panels are load centers with no main breaker just branch breakers. it all seems pretty tacky to me, i'm just trying to help out the owner with what he has. im getting ready for the install in two days and dont want to waste too much time on the job trying to figure this out. i know a lot of this may be redundant, but all the information given would be greatly appreciated. i have taken a look at the codes you have all mentioned earlier and im having a hard time. thanks
so that would mean that i would have to install 300 kcmil on the primary side according to the 75 degree column for the 270 amp current rating
can i take these conductors to the panels on the secondary side and i would also have to install ocpd on the secondary side before the panels. there within 7 feet of the transformer and the ampacity of the conductors are not less than the primary ocpd.