how to determine correct 2 pole breaker size in amps (3rd and final pic)


I need to install a breaker for my model HD-3 arco roto-phase rotary phase converter. it's basically rated "max single motor 3 hp, max total motors running at any one time 12 hp."
it'll be a 2 pole breaker, but what amps should I use? this image shows a nice closeup of the device nomenclature plate...
http://www.image-upload.net/files/5385/arco_tags.jpg
thanks for info guys :-)
toolie 'an electrically dumb guy'
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dave wrote:

Will depend on the rating of the motor you're running.
Go: http://www.arco-electric.com/ApplicationGuide.cfm Check out all the sections on the left pane.
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On Sat, 27 Sep 2008 19:58:32 -0400, Speedy Jim

Or......start with 20 and work your way up. :)
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wrote:

Short answer 8ga copper wire 50a breaker
455.6 and 455.7 say 125% of FLA of the total motor load. 12HP works out to around 38a but it is not specifically listed on 430.150 but 50a should cover it.
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According to the chart #10 wire and a 20 amp breaker is required. http://www.arco-electric.com/InstallationGuide.cfm
You did not mention what you plan to use the phase converter for, but make sure that you size it very carefully for the equipment that you want to connect to it. I've had a few customers over the years get these things and had them sized by the factory and in most cases they needed to be upsized. It not just the motor HP, but also the way the motors are used that affects the performance. Start-up current is one of the biggest problems.
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dave wrote:

The plate says no load amps are 8. So you could double or triple that. If you think it will take 16 amps at full load use a 20 if you think it will take 24 amps at full load use a 30 amp breaker.
--
Blattus Slafaly ? 3 :) 7/8

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