Another pond pump question

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Old 10-13-16, 07:06 PM
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Another pond pump question

Purchased Goulds GT 15 Irri-Gator pump for irrigation project.

Motor label states 16.8 amps for 115 volt. To me, this would be a 20 amp breaker. However, the instruction manual shows a much larger breaker being needed.


Would be significantly cheaper to use a regular single pole 20 amp breaker with GFCI outlet before the underground feeder to the pump for the 120v vs the 20 amp double pole GFCI breaker for the 240v.

Thoughts and assistance greatly appreciated.
 
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Old 10-14-16, 05:14 AM
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Electric motors draw much more current when starting. Your motor may draw 16 amps at full load when running but could draw double+ that when starting. That is why larger wiring and higher capacity circuit breakers are needed. Lower rated delay acting circuit can be used because they are designed not to trip when hit with the sudden inrush of current when something like a motor starts. Standard breakers trip almost instantly and must be sized to handle that initial surge of current.
 
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Old 10-14-16, 01:29 PM
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The manufacturer's table for overcurrent protection is a little excessive based on what the code allows for breaker sizing on motors, which routinely is up to 2x the FLA. A maximum multiplier of 2.5x of the FLA is the largest size permitted by code, and the mfr is recommending over 3x in some cases. However code does say to use the smallest breaker that will still allow the motor to start reliably, and only increase the breaker size if the breaker trips when the motor starts.

You should be looking at the Circuit Breaker / Delay column for modern breakers with an HACR rating which would be a 35A single pole or 20A double-pole breaker depending on the motor voltage.

I would wire this for 230V operation with a double pole 20A GFCI breaker using #12 copper wire if less than 100' If more than 100', increase to #10 copper wire.
 
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Old 10-14-16, 06:49 PM
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Thanks for the replies, your assistance is appreciated.

I will be wiring it for 230v. I already have the 20A double pole GFCI breaker and #12 underground feeder cable (run is 70').

I just saw the 16.8 amps on the motor plate and got excited about saving about $100 with a cheaper breaker and using a GFCI outlet by possible running it 120v.
 
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