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Introduction to Transformers and the National Electrical Code® in 2017 NEC. This is a multi-part series on understanding transformers and how they related to the National Electrical Code®. This episode builds on Part 1 and explains how to determine primary and secondary overcurrent protection based on section 450.3.
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Thank you so much. Love the videos. Can I still use these videos to studying for the calculations portion of my Texas Masters Exam. Or has there been any changes?
Greetings – Calculations are the same. The only difference is that things have been moved around.
Stephen, Im taking my Texas one as well, the 13th. Hopefully I pass it.
Good Luck!
Paul, Thank you so much for all the information! Ive gotten through many of the videos, what you do matters to a lot of people! Are there any other tips you have for the Texas exam? I missed the last one by 5 points each. :/
Texas Master
Did you Pass?….Is that what you are referring to. I sure hope so.
Shouldn’t the secondary protection be 250A only since 300A will exceed the maximum rating of 125%?
Sorry, you will need to be more specific in your question and example.
Sorry about that. In the example, the secondary feeder OCPD was sized to 300A which is the next higher rating (208A*1.25=260.42A). However, wouldn’t that 300A OCPD exceed the maximum rating or setting allowed on Table 450.3(B) Note #1? That is why I asked if instead of 300A breaker, should it be just at 250A so we do not exceed the 125% maximum rating? Thanks!
Greetings,
Sorry, I dont understand the comment. If the secondary OCPD is 208 Amps x 125% = 260 Amps. Note 1 would permit the OCPD to be increased to the next standard size, which is 300 Amps.
Where the required fuse rating or circuit breaker setting does not correspond to a standard rating or setting, a higher rating or setting that does not exceed the following shall be permitted:
a. The next higher standard rating or setting for fuses and circuit breakers 1000 volts and below, or
b. The next higher commercially available rating or setting for fuses and circuit breakers above 1000 volts.
Thank you for response.
I understand that Note 1 lets us go to the next higher standard rating but my concern was going with 300A OCPD, aren’t exceeding already the required maximum rating/setting of 125% (260A). So, in this example, you’re saying that we can still apply Note 1 even if it will exceed the maximum 125% rating/setting.
I hope it is clear. Thanks again!
What would be the purpose of Note 1 if you were not permitted to round to the next standard size? When it says 125% and you apply 125%, if a breaker doesn’t correspond then you are permitted by the note to go to the next size. This is similar to what is done in 240.4(B) as well.
This transformer series is great! Passed my WV Master exam a little while back and am taking a PA exam at the end of the month. Started listening to your podcast, then your youtube videos, then enrolled in Fast Trax Plus. This is a game changer for my family and I. I really appreciate what you’re doing for the trade!
Greetings Fella – Sorry for the late response. I am praying that it all turned out well for you and you nailed that exam in PA. I am so happy that our course is working well for you and that it also means future prosperity for your family. Remember, we are always here to help and the new Fast Trax Interact feature that is embedded in all the 2020 and 2023 courses will make it easy to post and get questions answered. Also Happy New Year to you and your family and make 2025 the Best Year Ever!
With an over 1000 volt transformer is the primary only chart only apply in delta delta or single voltage secondary the same as the under 1000 voltage chart. Can I have primary only protection scheme with a 12470v to 480v /277 v transformer?
Dan – I am not sure I follow you. If the transformer is over 1000V then you would follow the table 450.3(A) rather than 450.3(B). If the transformer is rated Over 1000V then you would use Table 450.3(A) and all applicable rules.