KP2
Senior Member
- Location
- New Milford, CT
In the Handbook Ex.240.9 Shows the Secondary to primary Ratio of 208/480 = .433. In 240.21(B)(3)(2) it says to use the Primary to secondary ratio. the way we see it the calculation schould go like this; 480/208=2.308. 2.308*36.667 = 84.627 amps. The 36.667 is one third of the OCPD of the primary.
In conclusion the secondary Tap conductor shall not be smaller than 84.627 amps. which would be a # 3 out of the 60 deg C column. If we use the .433 it tells us the smallest wire is 15.877 amps rated.
In conclusion the secondary Tap conductor shall not be smaller than 84.627 amps. which would be a # 3 out of the 60 deg C column. If we use the .433 it tells us the smallest wire is 15.877 amps rated.