Transformer sizing

iprogram · Dec 5, 2019

Been a long time since i have done any actual electrical design and want to make sure i am doing this correctly.

I have 480VAC 3 phase available and i need a transformer that can supply me with 120VAC single phase(one line with neutral) at 20 amps on the 120VAC side. So my old school math says a 3KVA transformer will be good like this one:
acme Item Number CE3000F007

Does this sound correct? I would wire the primary side with L1 and L2 to H1 and H4 (leaving L3 out) from the available 480vac. then on the secondary side i would use X1 and X2 for my output.

TheGreatAttractor · Dec 5, 2019

That is correct.

I would wire it like image 7 on the wiring diagrams found at https://www.galco.com/buy/Acme-Electric/CE3000F007 and the data sheet which you described.

Do not forget breakers or fuses on Primary and Secondary.

jraef · Dec 5, 2019

iprogram said:
Been a long time since i have done any actual electrical design and want to make sure i am doing this correctly.

I have 480VAC 3 phase available and i need a transformer that can supply me with 120VAC single phase(one line with neutral) at 20 amps on the 120VAC side. So my old school math says a 3KVA transformer will be good like this one:
acme Item Number CE3000F007

Does this sound correct? I would wire the primary side with L1 and L2 to H1 and H4 (leaving L3 out) from the available 480vac. then on the secondary side i would use X1 and X2 for my output.

20A x 120V = 2400VA, CPTs come in 2000VA or 3000VA, so yes, you picked the right one. Ground the X2 side of the secondary.

GaryS · Dec 5, 2019

What !
On the high connection for 480v is L1 to H1, L2 to H4 and H2 to H3
there is 2 windings on the primary side
H1 and H2 are one coil 240V H3 and H4 are the other coil 240V
if you don't connect H2 to H3 the circuit will be open and no current will flow - not output
X1 and X2 for the output coil 120V if its a singe voltage output
X2 should be connected to the panel ground (Bonding) Require by UL to keep from getting a floating high voltage in the 120V line

Transformer sizing

iprogram

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