Downsizing an Engineered panel

[Dennis Alwon]

58410 / (208/(sqr(3)) = 486
right answer

OR

58410/120 = 486

Much less complicated

 

[kingpb]

I will provide a good thing to learn; there is a difference between 120/208V and 208Y/120V.

120/208 is a single phase 3W system derived from a 208Y/120V system, and
208Y/120V is a 3ph, 4W system.

 

[Dennis Alwon]

I will provide a good thing to learn; there is a difference between 120/208V and 208Y/120V.

120/208 is a single phase 3W system derived from a 208Y/120V system, and
208Y/120V is a 3ph, 4W system.

I never heard of that as those numbers, in reality are often used either way. I do remember someone saying something similar to this...

 

[kingpb]

Beatings will continue until morale improves.

 

[kingpb]

I never heard of that as those numbers, in reality are often used either way. I do remember someone saying something similar to this...

That is true they are very often mistakenly used either way. There are a lot of engineers that use it incorrectly. I will say, prior to being an engineer, I was an electrician doing industrial work, and we made a lot of money on change orders every time they would put 120/208V on the drawings and we new they needed 208Y/120V.

 

[petersonra]

I never heard of that as those numbers, in reality are often used either way. I do remember someone saying something similar to this...

I have heard that differentiation before but I don't know if it's anything official.

 

[Mustang125]

I will provide a good thing to learn; there is a difference between 120/208V and 208Y/120V.

120/208 is a single phase 3W system derived from a 208Y/120V system, and
208Y/120V is a 3ph, 4W system.

haha now you have me really confused. do you have a couple diagrams?

 

[kingpb]

I have heard that differentiation before but I don't know if it's anything official.

I'm glad you asked.
Check ANSI C84.1, Table 3-1, note d., also found in IEEE Std 141.

 

[kingpb]

OR

58410/120 = 486

Much less complicated

Yes, indeed; but food for thought. Wouldn't this require a panel rated 800A; unless you can find a 600A, 100% rated breaker.
486 x 1.25 = 608A.

 

[david luchini]

Yes, indeed; but food for thought. Wouldn't this require a panel rated 800A; unless you can find a 600A, 100% rated breaker.
486 x 1.25 = 608A.

Why multiply the 486 by 1.25?

 

[Mustang125]

I'm glad you asked.
Check ANSI C84.1, Table 3-1, note d., also found in IEEE Std 141.

interesting, i have to admit. this stuff is now way over my head. haha

 

[jim dungar]

I'm glad you asked.
Check ANSI C84.1, Table 3-1, note d., also found in IEEE Std 141.

I find POCOs to be some of the worst offenders when it to using ANSI standard naming conventions.

 

[Dennis Alwon]

interesting, i have to admit. this stuff is now way over my head. haha

You are not alone, believe me. There are many who don't understand this stuff. Doing residential work it wasn't much of an issue. Life was simple for us dense individuals... haha

 

[Tulsa Electrician]

See if this helps.

3 phase panel calculations Help needed

So to try to simplfy this When I have (3) loads at (30amp 3phase 208v) I would calculate the panel as such: (30a x 208v X 1.37 / 3 ) or do I enter the total VA to each phase 10,807.68va? A phase B phase C Phase 3607 3607va 3607va...

forums.mikeholt.com

For a 120/208 three phase wye
Line kva / 120 for each line (A,B,C)
Total connected kva /208/1.732
It's important to understand that with single phase line to line loads you can over load one or two of the lines even if your total kva is under the panle ampacity rating.
An extreme example would be using you numbers. For the 600 amp panle. I moved single phase B-C load to A-B. Removing load from C placing it on A. B would remain unchanged.
A=78.41 KVA ( kva/120)
653.43 amps ( over loaded )
B= 54.41KVA. ( kva/120)
453.42 amps (kva/120)
C= 29.03 KVA
241.92 amps

Total 161.85 KVA
(total kva/208/1.733)
429.26 amps

By doing the schedule and balancing the loads the best they can you can use the lowest safest ampacity rating of the panel and feeder.
This will also provide a additional load calc that can be added if common sense is applied and the math is done.
So be careful moving single phase loads around with out doing the calculations for the three phase panle.
The the same can be done for netural loading.
Again be careful changing from a single 600 to any combination to get 600 with out doing the math using a scheldule.
There also may be other reasons the engineer chose what he did beside total connected load.

 

[Strathead]

haha I just don't get why electricians never what to help each other. our trade is so cut throat its sad really...
I understand not wanting to teach non electricians something they shouldn't be doing but not helping your own brothers seems a shame.
Nobody can understand or know perfectly how to do everything, our trade is so broad.

And I am not sure whether they are trying to still be obtuse, or just quick on their answers. Either you or the Engineer calculated the amps incorrectly. Phase A is 58,410/120 or 487 amps. The average amperage per phase is 161,850/208/1.73 that is VA divided by volts divided by the square root of 3.

 

[petersonra]

I'm glad you asked.
Check ANSI C84.1, Table 3-1, note d., also found in IEEE Std 141.

Does the NEC require one follow this particular standard?

 

[don_resqcapt19]

Does the NEC require one follow this particular standard?

No