By Bert Markgraf
Updated Mar 24, 2022

Many commercial and residential installations use a low‑voltage three‑phase system that delivers 120 V phase‑to‑ground and 208 V phase‑to‑phase. Household appliances and many industrial devices, however, require a 230 V supply. Running them on 208 V can cause reduced performance, overheating, or complete failure. A simple buck‑boost transformer can raise the voltage safely and efficiently.

Step 1 – Verify Transformer Ratings and Cable Size

Read the transformer’s nameplate to confirm the rated primary and secondary currents. Ensure the power cable is sized for that current and the distance to the load. Typical cable selections:

• AWG #14 for up to 15 A and runs up to 50 ft
• AWG #12 for up to 15 A on longer runs
• AWG #10 for up to 30 A
• AWG #8 for up to 40 A
• AWG #6 for up to 55 A

Match the breaker and disconnect switch ratings to the cable’s current capacity. Verify the transformer’s power rating can handle the load you plan to connect.

Step 2 – Mount the Transformer

Place the transformer close to the load to minimize cable length. For units above 3 kVA, stand them on the floor near a wall. Smaller transformers can be wall‑mounted using the screw slots in the feet. If the transformer isn’t pre‑wired in a 208/230 V configuration, follow the wiring diagram supplied by the manufacturer. Cut a length of power cable, strip the insulation, and prepare the conductors for connection. Install the disconnect switch on the wall about 4 ft above the floor, adjacent to the transformer’s 230‑V side.

Step 3 – Connect the Wiring

Use a multimeter to confirm the 208‑V two‑pole breaker supplies the correct voltage. Switch off the power before working. Run one cable from the breaker to the transformer’s 208‑V terminals. Use a second cable from the transformer’s 230‑V terminals to the disconnect switch. A third cable should run from the disconnect switch to the load.

Step 4 – Test the System

Open the disconnect switch, then restore power. Measure the voltage at the switch’s output; it should read 230 V. Close the switch and power the load to verify proper operation. If the load functions normally, the conversion is successful.

What You’ll Need

• 230‑V buck‑boost transformer
• 240‑V power cable (appropriate gauge)
• Two‑pole breaker
• Disconnect switch
• Multimeter

**Safety Note:** Always consult local electrical codes and, if necessary, hire a licensed electrician to perform the installation. Improper wiring can pose serious fire or shock hazards.