Transformer sizing

[welectrical]

If I have a 750kVA transformer 13.8:208Y/120V, the secondary OCP would be 3000A.

750/0.36*1.25 = 2600 -> next size up = 3000A.

However, if I don't need the full 750kVA could I downsize the OCP?
3000A is the maximum OCP, but theoretically could I put a secondary OCP of 2500A or even 2000A - knowing 2000A is more than I need?

Reason: the transformer is a spare transformer that the owner has on site, they want to use it for a temporary application to feed temporary distribution equipment, they would be renting the secondary OCP, and my thought is that 3000A frame is significantly more rare than a 2000A frame, so renting a 2000A frame would be both more cost effective and will have shorter lead times.

Thoughts?

 

[augie47]

You can install any size secondary you wish as long as the transformer & conductors are protected

 

[LarryFine]

However, if I don't need the full 750kVA could I downsize the OCP?
3000A is the maximum OCP, but theoretically could I put a secondary OCP of 2500A or even 2000A - knowing 2000A is more than I need?

Absolutely.

By the way, next-size-up allowance stops at 800a.

 

[infinity]

By the way, next-size-up allowance stops at 800a.

According to what Augie posted couldn't he still go up to the 3000 amp OCPD on the secondary? It doesn't sound like he was talking about the conductor size just the OCPD size.

 

[don_resqcapt19]

According to what Augie posted couldn't he still go up to the 3000 amp OCPD on the secondary? It doesn't sound like he was talking about the conductor size just the OCPD size.

Yes as Table 450.3(A) permits the next standard size for the 125% secondary protection. However, then he needs to use 3000 amps of conductor too.
I would be looking at the secondary OCPD and conductors sized only large enough to support the connected load.

 

[kwired]

According to what Augie posted couldn't he still go up to the 3000 amp OCPD on the secondary? It doesn't sound like he was talking about the conductor size just the OCPD size.

Yes as Table 450.3(A) permits the next standard size for the 125% secondary protection. However, then he needs to use 3000 amps of conductor too.
I would be looking at the secondary OCPD and conductors sized only large enough to support the connected load.

I agree that you need no less than 3000 amps of conductor if you have 3000 amps of overcurrent protection.

Actual rated current of this transformer is 2082 amps. I think one should at least do some careful studying of whether or not it can handle 2600 to 3000 amps and for how long at very least or if it can be uprated with additional cooling methods or such if you intend to have that much actual load connected to it.