Sizing Transformer Primary Conductors using rules in NEC 240.4 and T-310.16. [Code references are from the 2020 NEC, but most will correspond with prior editions.]
Hi DG, As usual, awesome session. I got a small doubt...can u please help... I understand that u have considered single phase formula for calculating the Transformer primary current..but aren't we suppose to go for 2 Phase formula since we are using two phase (480V) for the Transformer primary....
You are correct in that a #3 AWG copper conductor rated for 75 degrees C can handle 100A so it can easily carry the Full Load Amperage. The transformer would be adequately protected per T-450.3(B) and the load would be provided for. (If you are maximizing the output of the transformer with a "continuous load", make sure to also consider 210.19, 210.20 for branch circuits, or 215.2 and 215.3 for feeders.) This video focuses on the rules for "protecting the conductors" so if you did choose to use a #3 AWG copper conductor rated for 75 degrees C, the "conductor" would need to be protected by a 100A OCPD, also rated for 75 degrees C. As long as the characteristics of the OCPD allow for the inrush current to avoid nuisance tripping upon startup, a 100A fuse or circuit breaker paired with a #3 wire is a perfectly acceptable option. Thank you for your clarifying question.
Greetings from Mexico, your explanation was insightful
Great explanation. Thanks for making these videos!
Great videos .. keep doing more thanks
This is very helpful. Thank you!
Wow i learn so much from this video Sir,thanks a lot
Under what circumstances would we choose primary-only protection versus primary and secondary protection, or is it simply a matter of preference?
Awesome video, subscribed, my question is how low can go the OCPD ?
Hi DG,
As usual, awesome session.
I got a small doubt...can u please help...
I understand that u have considered single phase formula for calculating the Transformer primary current..but aren't we suppose to go for 2 Phase formula since we are using two phase (480V) for the Transformer primary....
Could you do a video.. how size wire ocdp, overload and wire ... for motors
Is there a code reference on how you came up with the 125amp OCP for 3phase transformer
Great video. Wondering why you are sizing using 75c? Aren't we suppose to use 60c column when the amperage is under 100amps?
I think most of these examples and code questions specify 75 degree column
is there a code reference to downgrade the max OCP?
@ 8:00 why did you not use #3 cable since it can handle 100A which is higher than FLA 90.3A ?
You are correct in that a #3 AWG copper conductor rated for 75 degrees C can handle 100A so it can easily carry the Full Load Amperage. The transformer would be adequately protected per T-450.3(B) and the load would be provided for. (If you are maximizing the output of the transformer with a "continuous load", make sure to also consider 210.19, 210.20 for branch circuits, or 215.2 and 215.3 for feeders.)
This video focuses on the rules for "protecting the conductors" so if you did choose to use a #3 AWG copper conductor rated for 75 degrees C, the "conductor" would need to be protected by a 100A OCPD, also rated for 75 degrees C. As long as the characteristics of the OCPD allow for the inrush current to avoid nuisance tripping upon startup, a 100A fuse or circuit breaker paired with a #3 wire is a perfectly acceptable option.
Thank you for your clarifying question.