Transformer secondary protection

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Wirenut21880

Member
Location
Yakima, Washington
Occupation
Electrician
I have a 2p50a breaker in a 480V panelboard feeding a single phase 25kva transformer with 120/240V secondary. The secondary is feeding a 125A rated 24 space panel 5' away. Do I need a main breaker in this panel, or am I exempt via 240.21(C)(2)?
 
Wirenut21880 said:
I have a 2p50a breaker in a 480V panelboard feeding a single phase 25kva transformer with 120/240V secondary. The secondary is feeding a 125A rated 24 space panel 5' away. Do I need a main breaker in this panel, or am I exempt via 240.21(C)(2)?
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You need a secondary side main breaker somewhere based on 408.36.
 
Since the primary protection exceeds 125% of the primary full load, the transformer itself needs a secondary OCPD. The panel OCPD that Jim mentioned in the previous post will protect both the panel and the transformer secondary.
 
don_resqcapt19 said:
Since the primary protection exceeds 125% of the primary full load, the transformer itself needs a secondary OCPD. The panel OCPD that Jim mentioned in the previous post will protect both the panel and the transformer secondary.
Click to expand...
Single phase transformer. The primary protection is less than 100% of the primary rated current.
 
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