I wish to power a remote (150ft away from dry-xfmr location) breaker panel with 120/240V 3W single phase. The breaker panel will have a main breaker.
I have 480V single phase on a 15amp breaker (smallest size) available to power a dry-transformer. The planned transformer(to supply the 120/240) is within 20 ft of the 480V breaker, to be fed with #10 wire. This is a separately derived system.
If I use a 3KVA transformer (6.3A FL@480V primary, 12.5A FL@240V secondary), do I need separate primary protection at the transformer, and/or any secondary protection?
If I use a 5KVA transformer (10.8A FL@480V primary, 20.8A FL@240V secondary), same question, or are the requirements a little different?
I am a bit confused with the NEC Table 450.3(B). For example if I use the 5KVA, the current exceeds 9amps(10.8A primary). However, the next(first) available breaker is 15amp for the primary protection. But 10.8/15 = 138%, greater than the 125% referenced. But the Note 1 seems to say this is still OK because the 15amp is the 'next' available breaker above the requirement. Or does this push the requirement into the second row of the table, 250% and both primary and secondary protection required? Am I saved anything if I use the 3KVA xfmr instead with primary current below the 9 amp threshold?
Any help here is appreciated.:-?
I have 480V single phase on a 15amp breaker (smallest size) available to power a dry-transformer. The planned transformer(to supply the 120/240) is within 20 ft of the 480V breaker, to be fed with #10 wire. This is a separately derived system.
If I use a 3KVA transformer (6.3A FL@480V primary, 12.5A FL@240V secondary), do I need separate primary protection at the transformer, and/or any secondary protection?
If I use a 5KVA transformer (10.8A FL@480V primary, 20.8A FL@240V secondary), same question, or are the requirements a little different?
I am a bit confused with the NEC Table 450.3(B). For example if I use the 5KVA, the current exceeds 9amps(10.8A primary). However, the next(first) available breaker is 15amp for the primary protection. But 10.8/15 = 138%, greater than the 125% referenced. But the Note 1 seems to say this is still OK because the 15amp is the 'next' available breaker above the requirement. Or does this push the requirement into the second row of the table, 250% and both primary and secondary protection required? Am I saved anything if I use the 3KVA xfmr instead with primary current below the 9 amp threshold?
Any help here is appreciated.:-?