Transformer OCPD - Pri. & Sec. Protection, Table 450.3(B)

Рет қаралды 34,677

3 жыл бұрын

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.]

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@Peace88Hi Жыл бұрын

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 !!!

@stepanvinnikov6024 Жыл бұрын

Had him as teacher now watching the video installing a step down transformer

@michaelhinchey Жыл бұрын

THANKS for the refresher. You are a very good instructor.

@bigjesskennelz 3 жыл бұрын

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.

@davegordon6819 3 жыл бұрын

Thanks. I'm glad it has helped you.

@mehardeepsingh5190 3 жыл бұрын

@@davegordon6819 May I please have your email? Got a stupid question 😅

@tonymag28 Жыл бұрын

Thank you so much for this EXTREMELY useful information. You are a savior

@luismota9846 3 ай бұрын

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)

@koryabel6319 2 жыл бұрын

Helped me navigate the tricky task of sizing transformer equipment

@koryabel6319 Жыл бұрын

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.

@jameslake1931 2 жыл бұрын

Love your videos for refreshing! 👍👍

@andrewvallejo2320 2 жыл бұрын

Your bad ass bro like how you break stuff down nice and simple make it easy for us to understand thanks for the video 👍

@josephcarlson7276 3 жыл бұрын

Great video! Thanks

@fernandovelasco4904 Жыл бұрын

Perfectly Explained.

@user-pk4pr6rs7g 4 ай бұрын

Why can't you go over the primary Max. OCPD, but you can go to the next size up on the secondary Max. OCPD?

@VuLe-zn1sm 2 жыл бұрын

thank you for your video

@comboangelgrace8467 Жыл бұрын

Very informative !

@EonTide1111 4 ай бұрын

I guess my other question would be why is the primary ocpd 250% not 125 % . Your videos are so thorough and helps a lot

@rachelcarantes5658 2 ай бұрын

THANKS

@altuber99_athlete Жыл бұрын

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?

@clifftonclaycromberg8733 Жыл бұрын

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

@m1r3nd3 2 жыл бұрын

very helpful!

@matthewrwalker 2 жыл бұрын

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.

@user-ei9bi6ep5b 10 ай бұрын

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.

@normanvictor2561 8 ай бұрын

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?

@jonmonte9977 Жыл бұрын

Now, do you have to size the conductors for 250% or based on the FLA?

@jolyonwelsh9834 Ай бұрын

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.

@wwatkin21 2 ай бұрын

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

@carloscifuentes1124 11 ай бұрын

i understand the Max OCPD is 250%. Is it incorrect if I use 125% for both Primary and Secdary side of the transformer?

@EonTide1111 4 ай бұрын

So the maximum ocpd is 250%. the minimum is 125% or 25% over of the fla ?

@edwrd1990 2 жыл бұрын

I’m confused. Aren’t you suppose to use 240V for the secondary?

@michaelhinchey Жыл бұрын

Its a y configuration.

@michaelhinchey Жыл бұрын

You can have a 416v y / 240v transformer.

@homeworkfive5040 10 ай бұрын

@@michaelhincheya 240V transformer is like a 208Y/120v circuit where the 240V is taken using the center tap?

@LS-fc7nx Ай бұрын

Proper voltage nomination would be 208

@michaelwas8549 3 жыл бұрын

do I need secondary OCPD on a buck boost single phase 208 to 230 transformer?

@RB-xv4si 3 жыл бұрын

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.