Transformer tap

[jim dungar]

What is the purpose of primary breaker? In theory would not the primary breaker if sized 125% protect the transformer from overloads?

Yes, that would be the case.

But remember if a transformer was intended to be overloaded, the primary side breaker would be sized based on the larger primary current.

According to Hammond Power Solutions, https://www.hammondpowersolutions.com/faq/can-i-increase-the-kva-rating-of-an-existing-transformer/
"[FONT=&quot]The most common way to increase the available kVA rating of an existing transformer is to add additional fan cooling."[/FONT]

 

[Muneepit]

Transformer Tap

Transformer Tap

I know this is an old thread, but, forgive my ignorance on this matter.

2017 NEC - Doesn't 240.3 (F) specifically say that the secondary conductors of a delta-wye transformer is not allowed to be protected by the primary side over current device or am I just reading that wrong?

You would then go by the tap rules?

 

[topgone]

I know this is an old thread, but, forgive my ignorance on this matter.

2017 NEC - Doesn't 240.3 (F) specifically say that the secondary conductors of a delta-wye transformer is not allowed to be protected by the primary side over current device or am I just reading that wrong?

You would then go by the tap rules?

Suggest you go to Table 450.3(A) for better understanding of transformer protection.

 

[kwired]

I know this is an old thread, but, forgive my ignorance on this matter.

2017 NEC - Doesn't 240.3 (F) specifically say that the secondary conductors of a delta-wye transformer is not allowed to be protected by the primary side over current device or am I just reading that wrong?

You would then go by the tap rules?

Assume you meant 240.4(F)? 240.3 has no sub parts, and yes the way I read it delta-wye secondary conductors is not considered protected by the primary overcurrent protection, there are unbalance conditions where you can overload a portion of the secondary yet not see overcurrent on primary conductors.

 

[GoldDigger]

Assume you meant 240.4(F)? 240.3 has no sub parts, and yes the way I read it delta-wye secondary conductors is not considered protected by the primary overcurrent protection, there are unbalance conditions where you can overload a portion of the secondary yet not see overcurrent on primary conductors.

Yes, that.
Just as you can overload a single phase transformer secondary without overloading the primary if the secondary has a center tap and the load is imbalanced.

 

[Wire-Smith]

Deleted