Three phase to single phase

[Jpflex]

I was just wandering how others would do this?

Company has a 4800 volt primary to 480 volt secondary pad mounted delta 3 phase transformer, I think at 50 KV? (boss selected 3/0 supply underground pvc) to (boss selected 200 ampere) 3 phase panel to power 3 phase motors

However coworker wanted to feed primary of 480 to 240 volt transformer from breakers on phase A and B of 3 phase transformer (instead of A and C for delta)


Also he could not fit the 3/0 wire (boss selected) primary wires into breakers in the 3 phase panel because breaker terminations are too small for large cables,

So would you use a Polaris tap go to 3 phase panel and splice to feed a smaller snap switch with fuse and terminating connectors large enough for primary cables?

 

[petersonra]

Your question is a little confusing. Maybe you could provide a sketch.

It does not matter which of the two three-phase lines you come off of to feed the single phase transformer. It can be any of the two.

It seems to me a 200 amp panel board ought to be able to handle 3/0 conductors. If not you'll have to adapt somehow but the best bet is just to get the right terminals that can handle the conductors.

Other than the mismatch between the terminal size and the conductor size I don't see anything wrong with what your boss selected.

 

[Jpflex]

Your question is a little confusing. Maybe you could provide a sketch.

It does not matter which of the two three-phase lines you come off of to feed the single phase transformer. It can be any of the two.

It seems to me a 200 amp panel board ought to be able to handle 3/0 conductors. If not you'll have to adapt somehow but the best bet is just to get the right terminals that can handle the conductors.

Other than the mismatch between the terminal size and the conductor size I don't see anything wrong with what your boss selected.

Three phase panel breakers do not have large enough terminals to feed primary of step down transformer. The transformer secondary will feed single phase panel

 

[petersonra]

Where is the 3/0 wire at? What is the rating of the cb that feeds the primary of the single phase xfmr?

 

[electrofelon]

And what size is the single phase transformer?

Edit: okay I see the single phase transformer in the attachment, 50 KVA. I think your biggest concern is how to feed the single phase transformer with a large enough ocpd so that it does not trip on startup. This three phase panel it is being fed from, what is it exactly? The largest two pole common breaker you can get is 125 which probably will work okay. It might not hold sometimes on startup but IMO that doesn't really matter if this is a plant type of setting where people know what's going on and it's not turned on and off frequently. If it doesn't take, just hit it again and it will probably hold. It might trip when the power comes on after a power outage, keep that in mind. You can typically get a larger than 125 two pole breaker but it will take up four spaces. For the 125 breaker, yes typically those terminals will go up to 2/0. They will take a 3/0 compact, but you probably have copper. Like you say, just use some splicers to reduce that down a bit.

Other options is if this is a panel board, maybe look into some feed through lugs or sub feed lugs and use the tap rules.

 

[Jpflex]

Where is the 3/0 wire at? What is the rating of the cb that feeds the primary of the single phase xfmr?

They decided 3/0 to primary and secondary wire feeding single phase panel.

200 ampere main breaker at single phase panel on load side of 3/0 secondary feeding it

 

[augie47]

If I understand, you have a 3/0 feeding your 50kva transformer so the conductor is too big for the breaker. IF that is correct, there would be no problem using a pigtail sized for the breaker ampacity and connect the pigtail to your 3/0 in the panel (via Polaris, etc)

A common practice when conductors are oversized for voltage drop.

 

[LarryFine]

Don't they make terminal pins that accept a conductor larger than the pin?

 

[electrofelon]

Don't they make terminal pins that accept a conductor larger than the pin?

Yeah, but I think you can only go like one size down if I remember correctly, but that might get him there..