#### letthesmokeout

Joined May 26, 2006
2
I am setting up a test here at work and need to know if the AC service I have will handle the load if I wire my power source as 3 phase delta. I have 16 DC power supplies that pull 20A AC each @ 208VAC. Is there a relatively simple formula a mechanical tech guy can use for this?

#### Erin G.

Joined Mar 3, 2005
167
Originally posted by letthesmokeout@May 26 2006, 03:36 PM
I am setting up a test here at work and need to know if the AC service I have will handle the load if I wire my power source as 3 phase delta. I have 16 DC power supplies that pull 20A AC each @ 208VAC. Is there a relatively simple formula a mechanical tech guy can use for this?
[post=17343]Quoted post[/post]​
Transformers are rated in KVA, or Kilo-VoltAmps. The formula is:

KVA = (E X I X 1.73) / 1000

Where E is Voltage, I is current, and 1.73 is a constant used for 3-phase calculations.

20Amps X 16 power supplies = 320 Amps. That's a heck of a lot of load! So:

KVA = (208 X 320 X 1.73) / 1000

KVA = 115,148.8 / 1000

KVA = 115.14

Two common 3-phase, 208VAC transformers are 100KVA (277.6 Amps) and 150KVA (416.4 Amps). Obviously, you'd have to go with the larger of the two. And you have to know that this is a pretty big transformer.

What kind of test are you running that requires 320 Amps?!

#### letthesmokeout

Joined May 26, 2006
2
Much grass! That looks like just what I need to know. We build telecomm power (AC/DC & DC/DC converters). I'm testing a battery plant that is going to be rated at 2400 amps DC, 24 &/or 48V. I am a mechanical tech and thermal testing for certification organizations (UL, VDE, etc.) fall into my realm which necessitates "dabbleling" in the eletrical world. I am very comfortable with DC & 1ph AC, but 3ph AC mathematics are somthing I'm not well schooled as yet.

#### Erin G.

Joined Mar 3, 2005
167
Originally posted by letthesmokeout@May 29 2006, 01:23 PM
Much grass! That looks like just what I need to know. We build telecomm power (AC/DC & DC/DC converters). I'm testing a battery plant that is going to be rated at 2400 amps DC, 24 &/or 48V. I am a mechanical tech and thermal testing for certification organizations (UL, VDE, etc.) fall into my realm which necessitates "dabbleling" in the eletrical world. I am very comfortable with DC & 1ph AC, but 3ph AC mathematics are somthing I'm not well schooled as yet.
[post=17400]Quoted post[/post]​

Go to Barnes & Noble, and in the science or tech sections, pick up a current copy of "Ugly's Electrical Referencs". It's a pocket-sized, spiral bound book with a yellow cover and red letters: Hard to miss. It will have all of the quick references you could ever need about most anything electrical, including laymen's terms explanations of it's contents.