Transformer OCPD - Pri. & Sec. Protection, Table 450.3(B)
HTML-код
- Опубликовано: 20 ноя 2020
- Sizing Transformer OCPDs on both Primary and Secondary sides using the Primary and Secondary Protection method. I reference NEC sub-sections 450.3(B), 240.6(A), and their tables. [Code references are from the 2020 NEC, but most will correspond with prior editions.]
Thank you so much. I am learning a lot from you. I have an Electrical Engineering degree, but never been lucky to get a good professor like the way you explained in your videos. Thank you again !!! You are the best !!!
THANKS for the refresher. You are a very good instructor.
Thank you so much for this EXTREMELY useful information. You are a savior
Just came across your channel and right away I subscribe. Love your videos. I'm currently going through this in class but you definitely explain it better. Keep them videos coming!! Thanx for you help.
Thanks. I'm glad it has helped you.
@@davegordon6819 May I please have your email?
Got a stupid question 😅
Had him as teacher now watching the video installing a step down transformer
Thank you Dave your explanation very clear. I didn’t understand why we have two time the standard 15 amps in table 240.6(A)
Your bad ass bro like how you break stuff down nice and simple make it easy for us to understand thanks for the video 👍
Helped me navigate the tricky task of sizing transformer equipment
1 year later I needed a refresher and helped me yet again. A wise old man told me use it or lose it and I lost it, but I got it back now. Thank you sir for the great video.
Love your videos for refreshing! 👍👍
Perfectly Explained.
Great video! Thanks
thank you for your video
Very informative !
Thanks, excellent video. How would the primary and secondary conductors be sized in this case (primary and secondary protection)? I suppose we’d use the max OCDP (60 A for the primary and 125 A for the secondary), not the FLA (25 A for the primary and 100 A for the secondary), right?
What if I use a secondary OCPD of 100 A (the same as the secondary FLA), would I still be required to size the secondary conductors to 125 A, or can I now size them to 100 A?
providing overvoltage protection at the high side of our 1500 kVA transformer to trip off the generation. We’re thinking of adding PTs and a relay to the delta side of our transformer and shunt tripping the LV breakers in our panelboards.
From a constructability perspective, my only concern is how the PTs will be installed on the high side of the transformer
very helpful!
THANKS
Can you add sizing of the conductors based on primary only calc and when calculating pri & secfor both single phase and 3- phase. Also, speak on the nuance of sizing based on ocpd vs downsizing the conductor using 240.4B in reverse.
I guess my other question would be why is the primary ocpd 250% not 125 % . Your videos are so thorough and helps a lot
Why can't you go over the primary Max. OCPD, but you can go to the next size up on the secondary Max. OCPD?
Trying to understand why we calculate the Max OPCD. Am I correct in my following assumptions? Cost wise you would want to select the OCPD as close to the FLA as possible . However, in some applications intermittent overcurrent can cause a headache with too much tripping of the breaker so some applications would want to go as high as possible which is what the Max OPCD provides the answer to.
If I have a 150kVA 208y/120 three phase transformer. 150,000/(208x1.732)=416.4 and since I’m not required to do 125% of the transformer current then I can size the breaker at 400A, but in that case wouldn’t it cause nuisance tripping since the transformer current is at just above 400A
What about working in a building that only has 208Y/120 and you are back feeding the transformer to create 480 volt for a piece of equipment.
The 208 volt input will have a bit of inrush current that would nuisance trip the breaker when turning on. Example 75 kva transformer, what breaker size and what formula to determine allowable ocpd?
25KVA is not a standard size for a 3 phase transformer. For a single phase yes. I would go with a 30KVA which is next closest example.
Now, do you have to size the conductors for 250% or based on the FLA?
i understand the Max OCPD is 250%. Is it incorrect if I use 125% for both Primary and Secdary side of the transformer?
I’m confused. Aren’t you suppose to use 240V for the secondary?
Its a y configuration.
You can have a 416v y / 240v transformer.
@@michaelhincheya 240V transformer is like a 208Y/120v circuit where the 240V is taken using the center tap?
Proper voltage nomination would be 208
do I need secondary OCPD on a buck boost single phase 208 to 230 transformer?
No, you don’t. You are allowed to use protection only on the primary side, but if you go this route, the ocpd may not be sized any more than 125% of the primary amp rating.
So the maximum ocpd is 250%. the minimum is 125% or 25% over of the fla ?
why 2.5 time for primary current??? Not understood
Why didn’t you use the square root of 3.
Why wouldn't the secondary be 240?
ITS A Y configuration in the secondary.
@@michaelhinchey On the single phase configuration of the first transformer.
Visually, you look wound tighter than the transformers. Do not forget to relax.
A 12 kV 120/240 volt transformer has 120 kVA on the primary side. What is th3e kVA on the secondary side?