Anyone care to help confirm my thinki...

Anyone care to help confirm my thinking on the 3PH to Single Phase??? Please!

DownTownFool

Houston, TX

#1 Dec 7, 2012
Ok, here are the facts:

I have 3PH 480 coming in from the power company (kVA is irrelevant at this point).

I want to install the following:

Three (3) single phase 480 to 240/120 25kVA transformers
One (1) single phase 480 to 240/120 10kVA transformer
One (1) 15HP 480V 3PH motor

According to Ugly's Book which references NEC, a single phase 25kVA has a FLA of 52.1, a single phase 10kVA transformer has a FLA of 20.8, and a 3PH 15HP motor has an FLA of 24.15 (FLA's obtained from Ugly's Book).

They will be wired as follows:

1phase 1phase 1phase 1phase 3phase
25kVA 25kVA 10kVA 25kVA 15HP
Phase - A X X X X

Phase - B X X X

Phase - C X X X X

Does this mean EACH phase will see the following amperage?

Phase - A - 52.1 + 20.8 + 52.1 + 24.15 = 149.15A

Phase - B - 52.1 + 52.1 + 24.15 = 149.15A = 128.35A

Phase - C - 52.1 + 52.1 + 20.8 +24.15 = 149.15A

For a given 480V to 240/120 single phase transformer...will BOTH primary 480V legs ( say A and B for the first 25kVA listed above) see the same current (52.1 amps assuming the transformer is 100% loaded)?

OR

will BOTH primary 480V legs see 26.05A (half of the 52.1 amps assuming the transformer is 100% loaded)?

Tell me when this thread is updated:

Subscribe Now Add to my Tracker

Add your comments below

Characters left: 4000

Please note by submitting this form you acknowledge that you have read the Terms of Service and the comment you are posting is in compliance with such terms. Be polite. Inappropriate posts may be removed by the moderator. Send us your feedback.

Electrical Engineering Discussions

Title Updated Last By Comments
Will a 150amp GE bolt on breaker fit into a GE ... Mar '18 Donald 1
News Falkirk student gains A 10k boost for space age... Feb '18 Walter glen stock... 2
Load Calculation for Office Blg. (Apr '17) Dec '17 jsykes 2
certification / re-certification (Jan '17) Dec '17 jsykes 3
John (Nov '17) Dec '17 jsykes 2
Electrical Load Calculations Dec '17 jsykes 1
Complete Noob Question (Apr '17) Apr '17 Enargins 1