running two 5 HP motors on the same circuit

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Old 11-14-19, 07:56 AM
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Question running two 5 HP motors on the same circuit

I have 2 single phase 220v machines that draw 25 amps each (5HP motors). I would like to run both machines at the same time. I wondering if going with twin 30 amp breakers with 10 gauge wire would be enough for this or do I need to think about a different set-up?
 
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Old 11-14-19, 08:15 AM
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Welcome to the forums.

Usually motors of that size are protected by starters and are on two circuits.
Two 25A motors would require at a minimum a 2P50 breaker which would not take into account any additional starting load. You would need at least #8 wiring and more likely #6.
 

Last edited by PJmax; 11-14-19 at 08:36 AM.
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Old 11-14-19, 08:29 AM
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@PJmax thanks for the information and thanks for the warm welcome. Are you saying the a 2P50 breaker with #6 wire would be sufficient to run both motors at the same time on the same circuit? Or should I consider separating this out into 2 separate circuits each with 2P30 breaker and #10 wire?
 
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Old 11-14-19, 08:39 AM
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Devices like motors usually have a maximum fusible circuit rating. When you put two motors on the same circuit you need to double the circuit size. That means either motor would not be protected properly from a direct short.

The other problem with two motors on the same circuit is the start up load. If they are both starting at the same time the circuit will need to be larger yet.

I would recommend the motors be on different circuits. If you need them both to turn on at the same time then you will need a contactor or two.
 
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Old 11-14-19, 09:13 AM
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@PJmax thanks again. When you say contactor or two, what do you mean by that?
 
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Old 11-14-19, 09:34 AM
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Twin breakers are not normally 240 volts. Usually both breakers are on the same leg of the service. Make sure you have the correct breakers for 240 volts.
 
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Old 11-14-19, 10:13 AM
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PJmax

.. That means either motor would not be protected properly from a direct short.
Well... this is not actually correct about the short protection. The motors can be on one circuit if hardwired and as long as the two motors have their own overload protection. The breaker only serves as short circuit protection and the short protection is not relative to the breaker amp size. Shorts are infinite amp draw and the short trip is the same if the breaker is a 30A or a 50A. The circuit needs to be sized to the total HP load of 10HP which is 50A X 125% = 62.5A. This will require #6Cu THHN in pipe or #4Cu NM-b. The breaker can be upsized up to account for startup loads. See NEC table 430.52 .
 
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Old 11-14-19, 05:23 PM
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The tool may not be on (be connected to) a branch circuit breakered at a greater amperes rating than the tool is spec'ed out for. Install a subpanel with separate breakers for each tool or run separate branch circuits for the two tools.

The maximum amperes rating may or may not be printed on the tool's nameplate. You could also go by the instruction manual or installation manual. It is rare that the maximum amperes rating for a tool will be great enough for two tools drawing comparable running amps to be on the same branch circuit.
 
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