Measuring Three-Phase 480-Volt Shop Voltage
From the original questioner:
Thanks. You are right. I did measure across one leg to ground.
From contributor L:
I'm not positive about this, but you should find 120 VAC across a hot and a neutral.
From contributor T:
The 480 VAC will be 277 from each hot leg to neutral. In three phase applications, the 480 typically is stepped down to 208 VAC. Then, each hot leg off the step down transformer will be 120 VAC hot to neutral.
From contributor J:
You have what is called a 480Y service coming into your building. It is a 3ph 4 wire service. You have 3 hots, a neutral, and a ground wire. The voltage between any one leg and ground will be 277 volts, and between any 2 hot wires will be 480 volts.
3 phase machinery runs off Delta voltage, which means you only run 3 hot wires and no neutral wire. If you mistakenly wire a 230 volt machine at 480, it will not run faster. It will most likely burn the motor up. Voltage does not affect the RPM of a motor, but the frequency of the voltage does.
You will need a transformer for your 120/208 1 and 3 phase loads. You will need a 480Y primary x 208Y secondary transformer.
In my shop, I used another transformer for my 230 volt 3 phase loads. I use a 480D x 240D transformer. All my motors are rated at 230 volts. Your motors will run a little cooler and draw slightly less amperage if you run them at 240 volts as opposed to 208. 208 only really works well with motors that specifically say 208-230 on the nameplate. Generally foreign motors are rated at 220-230 volts.
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