Rotary Phase Converters Breaker Size

Phase Converter Checklist

Get the right phase converter.

Checklist

What breaker size do I need?

If your 3 phase machine says it needs 100A, then it actually needs 173A of single phase power. Crazy, eh?

When doing phase conversion, you are creating a third electrical phase and the power to create that third phase needs to come from somewhere. Whatever your machine says it needs in 3 phase amps, multiply that by 1.73 to determine what it needs in single phase amps.

Breakers can only be loaded up to 80% of their rated capacity. So a 100A breaker can only support a sustained load of 80A. 

Example:
  100 Amps in 3 Phase = 173 Amps in Single Phase
  173 Amps / 80% Breaker Max Load = 216 Amp Min Single Phase Breaker

Breakers come in discrete steps. You will need to select the breaker size just larger than the minimum amperage required. If a breaker is too small, then it will needlessly trip. If a breaker is too large, then your machine will not be protected.

Do I really need a breaker that big?!?!

Probably not. Each converter has a recommended breaker size but this assumes the phase converter is running at maximum output. You need a breaker big enough to support whatever machines you will be running. If the phase converter is rated to draw 200A, it doesn’t mean that it WILL draw 200A. It will only draw what it needs to operate. If your machine is less than 200A in 3 phase, then you don't need a breaker for the full 346A.

Breaker Size Calculator

This tool will allow you calculate the breaker size that you need. The "3 Phase Output" is what your machine needs to run. The "Single Phase Input" is the power source you have, or need to have, available.

Single Phase Input
Your power source
Voltage:
Amps:
*Breaker:
3 Phase Output
Your machine's requirements
Voltage:
Amps:

*Breaker - This is the minimum sized breaker needed to run just your machine. It does not include the power required to run the phase converter.
A Digital Phase Converter requires almost no extra power but a Rotary Phase Converter needs to spin a generator and that does require some additional power.

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