# Undersizing OCPD for Motor



## Br4nd0n (Jul 10, 2012)

When sizing the OCPD for a compressor I'm installing, I get 70A @ 250% FLA. How likely will I experience problems, like nuisance tripping, if it's installed on a 60A breaker instead?


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## JRaef (Mar 23, 2009)

Br4nd0n said:


> When sizing the OCPD for a compressor I'm installing, I get 70A @ 250% FLA. How likely will I experience problems, like nuisance tripping, if it's installed on a 60A breaker instead?


You don't say what the motor FLC is.


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## Br4nd0n (Jul 10, 2012)

10 HP / 240V-3P / 24A . Table shows 28A x 250% = 70A. I am having trouble Tracking down 70s, but have 60s available.


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## nolabama (Oct 3, 2007)

http://m.lowes.com/mt/www.lowes.com/pd_67567-296-QO270CP_0__?productId=3129225

You can find seventies. To OP What is FLC?


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## Br4nd0n (Jul 10, 2012)

Yes, the supply houses can order one out, but I need it running today. I've tried several places. 28A is the FLC.


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## JRaef (Mar 23, 2009)

It's going to depend on the breaker. If the mag trip setting is non-adjustable and fixed at 4x the rating, as some are, you might be in trouble. 24A FLC on a newer Energy Efficient motor might have an instantaneous inrush of up to 17x FLC, so that's 408A, / 60A CB rating = 6.8x FLC. But if the mag trips are set at 10x FLC or adjustable to be as high as 408A, should be fine.


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## nolabama (Oct 3, 2007)

Put the sixty in run it and see what happens. If it holds till you get the seventy great if not they will have to wait.


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## Br4nd0n (Jul 10, 2012)

I appreciate the responses guys.

JRaef - the breaker type is BA (Cutler-Hammer). I looked up the technical data sheet, but could the only info I got was that the "mag will only trip under sustained overload".


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## JRaef (Mar 23, 2009)

Looking at a general trip curve for non-interchangeable trip CH breakers, the low side pick up point for their instantaneous trips appears to be around 7x the rating, so you should be fine.


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## nolabama (Oct 3, 2007)

JRaef said:


> Looking at a general trip curve for non-interchangeable trip CH breakers, the low side pick up point for their instantaneous trips appears to be around 7x the rating, so you should be fine.


Where does one find this sorta thing ?


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## JRaef (Mar 23, 2009)

nolabama said:


> Where does one find this sorta thing ?


http://www.circuitocinco.com/files/Breakers_CH.pdf

Most of the major mfrs provide what they call a "Consultant's Technical File" (or something similarly named) site where they provide the kind of information that consulting engineers usually look for. We use a lot of C-H breakers, so I have this one bookmarked, given to me by someone else.


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## Br4nd0n (Jul 10, 2012)

I appreciate all the information! I've got the 60A breakers in, but the customer's compressor guy never came - maybe today. Hope they hold!


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## John Valdes (May 17, 2007)

Br4nd0n said:


> I appreciate all the information! I've got the 60A breakers in, but the customer's compressor guy never came - maybe today. Hope they hold!


And the correct breaker has been ordered and could be there BEFORE the compressor guy comes in?


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## Br4nd0n (Jul 10, 2012)

I did go ahead and order the 70A breakers, but they won't be in until Monday at the earliest. It was confirmed to me that the compressor guy is scheduled for today.


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