Emery08
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- Powder Springs, Georgia, USA
What size feed do i need to feed a 480v to 230v 25kva single phase transformer
Transformer feed
- Thread starter Emery08
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It's going to depend on how you choose to protect the transformer and the OCPD rating on the primary. Rated primary current is 25,000VA ÷ 480V = 52A. See Table 450.3(B). 125% is 65A. The protection schema available to choose from are Primary Only, and Primary And Secondary. Quite often inadvertent secondary protection presents itself in the form of load-side panel protection... but this does not mean you have to use the P&S schema.
Julius Right
Senior Member
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- Electrical Engineer Power Station Physical Design Retired
According to NEC Table 450.3(B), Art.215.2.1(a) and 240.4,
in my opinion, 125% of rated current will be 65 A primary and 136 A secondary. A 70 A breaker for primary and 150 A for secondary and as per Table 310.15(B)(16) 4awg primary and 1/0 secondary as a minimum cross section area for copper conductor 75oC insulation.
You have to check the voltage drop-no more than 5% total [3% per feeder.] Art.215.2.1(b)
Informational Note No. 2.
in my opinion, 125% of rated current will be 65 A primary and 136 A secondary. A 70 A breaker for primary and 150 A for secondary and as per Table 310.15(B)(16) 4awg primary and 1/0 secondary as a minimum cross section area for copper conductor 75oC insulation.
You have to check the voltage drop-no more than 5% total [3% per feeder.] Art.215.2.1(b)
Informational Note No. 2.
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