Transformer and panel on secondary

[dm9289]

Could you have a 15kv transformer fed by 2 legs of a 480v wye to a 120/240 single phase secondaryoutput with no secondary protection (200 amp main in panel).
Oh sorry primary would have 40amp fusing.

I believe from 450 chart for transformer you can do primary only protection.

I also believe the main for that panel fed from secondary is necessary and about 85 amp breaker.
Is that breaker required in the panel and if so I assume a 200 amp would not be code compliant. I could not find the rule

 

[augie47]

Three rules apply:
450.3 stipulated transformer protection.
408.36 requires the panel have a main breaker (integral or ahead o it)
240.21(C) requires secondary protection on an single phase transformer with 3 wire output.

If the transformer primary protection meets the 125% rule then the secondary protection only needs to meet the 408.36 rules and can be sized based on the panel rating and the conductors.
Obviously there would be no need but you could use a 200 amp M/B panel with 3/0 conductors.

 

[dm9289]

Three rules apply:
450.3 stipulated transformer protection.
408.36 requires the panel have a main breaker (integral or ahead o it)
240.21(C) requires secondary protection on an single phase transformer with 3 wire output.

If the transformer primary protection meets the 125% rule then the secondary protection only needs to meet the 408.36 rules and can be sized based on the panel rating and the conductors.
Obviously there would be no need but you could use a 200 amp M/B panel with 3/0 conductors.

Ok thank you, I thought the panel main would have to be based on secondary capabilities. I guess you could use a large breaker say a 200 just for ability to disconnect.

 

[Elect117]

Ok thank you, I thought the panel main would have to be based on secondary capabilities. I guess you could use a large breaker say a 200 just for ability to disconnect.

The NEC handles transformer protection, conductor protection and panelboard protection separately. So as long as they are all protected respective to their section requirements as Augie mentioned above you are okay. At least from a NEC perspective.

 

[dm9289]

The NEC handles transformer protection, conductor protection and panelboard protection separately. So as long as they are all protected respective to their section requirements as Augie mentioned above you are okay. At least from a NEC perspective.

Yeah just seems counterintuitive to me. But I guess that’s just me