[Service Call]

Ive got a 480 feed to a 480/208-120 transformer. It's fed off a 200 amp existing 480 brkr. Out of the transformer I'm feeding a 120/208 panel with a 400 amp main breaker. The 480 breaker is located about 225 ft away from the transformer but yet within sight of. It's a warehouse. My question is do I need to put in a 300 amp over current protection on the secondary side of the transformer? We are on the '08 code if that makes a difference.

 

[micromind]

What is the KVA rating of the transformer? And is it 1 or 3ø?

 

[Service Call]

What is the KVA rating of the transformer? And is it 1 or 3ø?

112.5 Kva 3ph. Thought I had put that in the original post, but didn't.

 

[360max]

Ive got a 480 feed to a 480/208-120 transformer. It's fed off a 200 amp existing 480 brkr. Out of the transformer I'm feeding a 120/208 panel with a 400 amp main breaker. The 480 breaker is located about 225 ft away from the transformer but yet within sight of. It's a warehouse. My question is do I need to put in a 300 amp over current protection on the secondary side of the transformer? We are on the '08 code if that makes a difference.

so your 400A panel is now a 300A panel. Within site, as defined by the NEC means no more than 50 feet away and within site (see section 100- Definitions; 'In Site From')

 

[ponyboy]

Your disconnect for the transformer primary is allowed to be in a remote location as long as it can be locked open. If this was my install and I had to be cost conscious I'd set it up just with what you got. Not sure where 300 amp anything came into your equation though. If your secondary has a 400 amp main and your transformer is 112 kva then you're all set

 

[Service Call]

Your disconnect for the transformer primary is allowed to be in a remote location as long as it can be locked open. If this was my install and I had to be cost conscious I'd set it up just with what you got. Not sure where 300 amp anything came into your equation though. If your secondary has a 400 amp main and your transformer is 112 kva then you're all set

Maybe my math was wrong. I thought 112.5 Kva at 208 was only good for something like 290 amps. If I'm wrong then that's ok by me.

 

[Chrisibew440]

You get 200 amp out of a 75 kva.

 

[360max]

Maybe my math was wrong. I thought 112.5 Kva at 208 was only good for something like 290 amps. If I'm wrong then that's ok by me.

secondary amps is actually 312A

112.5kva/ (208x1.73)= 312A

 

[360max]

You get 200 amp out of a 75 kva.

huh???????????///

 

[micromind]

huh???????????///

75KVA at 120/208 3ø is 208 amps.

 

[Chrisibew440]

huh???????????///

Huh???????????? What were you missing?

 

[ponyboy]

Maybe my math was wrong. I thought 112.5 Kva at 208 was only good for something like 290 amps. If I'm wrong then that's ok by me.

You are correct. I was thinking of a 150. I can't remember the last 112.5 I did, they are useless to me.

That being said I'd look into refitting your secondary panel to a MLO maybe

 

[360max]

What is the KVA rating of the transformer? And is it 1 or 3ø?

]112.5 Kva 3ph. Thought I had put that in the original post, but didn't.

[/B]

Huh???????????? What were you missing?

112.5kva
:whistling2::whistling2::whistling2::whistling2:

 

[Chrisibew440]

[/B]


112.5kva
:whistling2::whistling2::whistling2::whistling2:

It was just to show that you can get 200 amps out of a 75. In another words 75 x 2= 150 and so fourth. He came up with 290 at 112.5 kva.



Is that ok with you?

I'm an idiot. I meant 2, 75 kvas would be 400 amps.

 

[micromind]

112.5KVA at 120/208 is 312 amps. A 400 amp breaker is compliant.

150 is 416. A 600 is ok.

 

[don_resqcapt19]

While the 400 amp OCPD in the panel is compliant for the protection of the transformer secondary, the secondary conductors must have an ampacity of at least 400 amps. You are not permitted to use 240.4(B) for this application. In other words, you need to install 600kcmil copper, not 500kcmil for the secondary conductors.

 

[mwbc4ever]

While the 400 amp OCPD in the panel is compliant for the protection of the transformer secondary, the secondary conductors must have an ampacity of at least 400 amps. You are not permitted to use 240.4(B) for this application. In other words, you need to install 600kcmil copper, not 500kcmil for the secondary conductors.

The secondary conductors also must be protected within 25' unless this meets the "supervised installation" requirements.