I have a system that is running on 208 VAC. I plan to use a 10 kVA buck boost transformer to power two electrodes. The transformer has input connections for 120 & 240 V, & output connections for 16 & 32 V. The desired design is to feed the 240 V input connection with 208 V to get 27.73 V on the 32 V output connection.

One of my main concerns is that the wires coming out of the transformer 32 V output connection are only 4 AWG wires, but we intend to pretty much run the transformer at its full load current. From the transformer manufacturer's datasheet, it lists that the full load current for the 32 V output connection to be 312 A.

I guess my confusion is that even if the transformer was being fed 240 V instead of 208 V, how would size 4 AWG wires be able to handle 312 A?

Transformer Datasheet Link: [1]: https://hubbellcdn.com/installationmanuals/A-22497-K.pdf

Using a "T-2-13079" transformer on page 3.

I'm an inexperienced engineer and don't have another engineer to ask about this.

  • \$\begingroup\$ What's a buck boost transformer? \$\endgroup\$
    – Andy aka
    Aug 2 at 14:02
  • \$\begingroup\$ (ACME seems to have had an idea what a buck boost transformer is - way back when (autotransformer with input&output voltage close to each other? Isolation transformer misused as an autotransformer?!).) (I put differences in conductor cross sections between installation and machines down to different allowable temperature rise.) \$\endgroup\$
    – greybeard
    Aug 2 at 14:24

2 Answers 2


The following chart shows the 'nameplate' and 'application' ratings of the transformer.

Losses are ignored as transformer efficiency could be as high as 99.7 %

enter image description here

You are mistaken. The secondary cable size would be 0000(4/0) AWG not 4 AWG.

  • \$\begingroup\$ This is what the inside of the Transformer looks like. imgur.com/a/ZC3I7fa The wires coming out of it are 4 AWG. My understanding is that 4 AWG Wires can only handle 85Amps so im not sure how the MFG rated the FLA as 312Amps. Does the resin looking material affect how much current the wires can handle? \$\endgroup\$ Aug 3 at 13:42
  • \$\begingroup\$ Hi Jack, Perhaps a number of 4 AWG cables have been connected in parallel. \$\endgroup\$
    – vu2nan
    Aug 5 at 8:40

"I guess my confusion is that even if the transformer was being fed 240 V instead of 208 V, how would size 4 AWG wires be able to handle 312 A?"

They don't care. They will be just as hot at 312 A at 27.73 V as they would have at 312 A at 32 V.

Decreasing the input voltage won't have any adverse effects other than lower output voltage and therefor lower total VA rating. Core losses will be slightly lower to due less excitation.

  • \$\begingroup\$ my concern is that 4 AWG cant handle 312Amps \$\endgroup\$ Aug 2 at 17:39
  • \$\begingroup\$ See @vu2nan’s answer above. Still, does not change my answer regarding voltage change. \$\endgroup\$
    – winny
    Aug 2 at 18:02

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