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 !!!
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.
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.
See Table 450.3(B) Note 1. Where 125 percent of this current does not correspond to a standard rating of a fuse or nonadjustable circuit breaker, a higher rating that does not exceed the next higher standard rating shall be permitted.
In a furnace you have a 24 volt transformer usually rated at 40 va. A volt amp is almost the same thing as a watt. So 2 amps would be 48 volt amps (or close to it). Why do they use 3 amp (or sometimes 5 amp) fuses?
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
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.
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?
note three, in table 450.3B allows where 125% does not correspond to a standard rating fuse or nonadjustable CB, a higher rating that does not exceed the next higher standard rating shall be permitted... however 240.21C Transformer Secondary Conductors does not permit 240.4B (round up rule)… so which one is correct? when can I and cant I round up for secondary side conductors? any feedback is much appreciated.
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?
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
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.
after watching this exact video, it says on 450.3 (b) since it needs primary and secondary protection and its 9+ amps you use 250% on the primary side only
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.
Omg thanks man i am halfway through my apprenticeship and was struggling to grasp the concept, this really helped thanks.
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 !!!
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 😅
Thank you so much for this EXTREMELY useful information. You are a savior
Had him as teacher now watching the video installing a step down transformer
THANKS for the refresher. You are a very good instructor.
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 👍
I guess my other question would be why is the primary ocpd 250% not 125 % . Your videos are so thorough and helps a lot
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.
Why can't you go over the primary Max. OCPD, but you can go to the next size up on the secondary Max. OCPD?
See Table 450.3(B)
Note 1. Where 125 percent of this current does not correspond to a standard rating of a fuse or nonadjustable circuit breaker, a higher rating that does
not exceed the next higher standard rating shall be permitted.
In a furnace you have a 24 volt transformer usually rated at 40 va. A volt amp is almost the same thing as a watt. So 2 amps would be 48 volt amps (or close to it). Why do they use 3 amp (or sometimes 5 amp) fuses?
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
Love your videos for refreshing! 👍👍
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.
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?
Great video! Thanks
Perfectly Explained.
note three, in table 450.3B allows where 125% does not correspond to a standard rating fuse or nonadjustable CB, a higher rating that does not exceed the next higher standard rating shall be permitted... however 240.21C Transformer Secondary Conductors does not permit 240.4B (round up rule)… so which one is correct? when can I and cant I round up for secondary side conductors? any feedback is much appreciated.
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?
i understand the Max OCPD is 250%. Is it incorrect if I use 125% for both Primary and Secdary side of the transformer?
Thank you very very very much.
In the denominator of both those formulas u need to multiply by 1.73
So the maximum ocpd is 250%. the minimum is 125% or 25% over of the fla ?
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
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.
Now, do you have to size the conductors for 250% or based on the FLA?
why 2.5 time for primary current??? Not understood
after watching this exact video, it says on 450.3 (b) since it needs primary and secondary protection and its 9+ amps you use 250% on the primary side only
Very informative !
Why wouldn't the secondary be 240?
ITS A Y configuration in the secondary.
@@michaelhinchey On the single phase configuration of the first transformer.
thank you for your video
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.
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
Why didn’t you use the square root of 3.
THANKS
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.
very helpful!
A 12 kV 120/240 volt transformer has 120 kVA on the primary side. What is th3e kVA on the secondary side?
Visually, you look wound tighter than the transformers. Do not forget to relax.