Do I have an oversized Main Breaker?

[Snowjob]

I have a 225 KVA transformer 12470/208 Wye Wye feeding my facility.
The transformer has 12470 VAC Cooper RTE Bay O Net fuses, #09, on its primary.

1. The Main Disconnect Device is a Square D Micrologic MX 36800 Breaker with a 800A sensor unit. An abandoned fused disconnect switch is adjacent to it.
   
2. Underneath it are two LX36600 breakers, both at 600A, One feeds the Critical panel and the other feeds the Essential panel.
   
3. The full load current on a 225 KVA transformer at 208 V is 625 A.
   
4. The 800A Main Disconnect Breaker is wreaking havoc on my Coordination and Arcflash calculations. Luckily the Transfomer fuses are there.
   
5. One minor thing. The 225 KVA Transformer is fed from a pole 2 miles away on a remote mountain thats often snowed in. If the transformer primaries blow, it might take up to 2 days for someone to climb the pole and restore service.

What are the implications of this 800 A Main Breaker?
( Should I ask them to hook up the bypassed fused disconnect switch?)

 

[don_resqcapt19]

Assuming that the secondary conductors have an ampacity of 800 amps or more, I don't see a code issue. 125% of 625 is 781 and Note 1 to Table 450.3(B) permits you to round up to the next standard OCPD size for the transformer secondary protection. The coordination and arc flash issues are design issues and not code issues.

 

[Smart $]

Regarding item #3, how did you establish this value?

 

[Mayimbe]

Regarding item #3, how did you establish this value?

I=225kVA/[sqrt(3)*208V]

 

[Snowjob]

Thanks

Thanks

Assuming that the secondary conductors have an ampacity of 800 amps or more, I don't see a code issue. 125% of 625 is 781 and Note 1 to Table 450.3(B) permits you to round up to the next standard OCPD size for the transformer secondary protection. The coordination and arc flash issues are design issues and not code issues.

Thank you very much, that was the exact answer I was searching for

 

[Smart $]

I=225kVA/[sqrt(3)*208V]

I knew that... but for some reason I was thinking load current rather than rated output current.

 

[Mayimbe]

I knew that... but for some reason I was thinking load current rather than rated output current.

I knew you knew that, but for some reason I thought you were thinking about load current instead of outpout current.

 

[Smart $]

I knew you knew that, but for some reason I thought you were thinking about load current instead of outpout current.

lol ...