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Welsh Andile
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Join Date: Apr 2011
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Overload Setting

04/27/2011 3:48 PM

what is the appropriate current setting of an overload protector as a percentage of F.L.C
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North of 60
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#1

Re: Overload Setting

04/27/2011 4:12 PM

As stated many times in this forum... such things depend upon the codes in your jurisdiction.

In Canada... the following applies.

CEC rule 28-306 states...

125% for a motor with a service factor of 1.15 or greater

115% for a motor not marked as to service factor or with a service factor less then 1.15

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JRaef
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#2

Re: Overload Setting

04/27/2011 5:26 PM

Most overload relays on the market have the pick-up points already faqctored into their design. You set them for the motor nameplate FLC, nothing else. In the case of NEMA style OL relays with replaceable thermal elements, if you have a motor with a 1.0SF (or unmarked where you must assume as much) then you can select the next size LOWER heater element. That's because with the prevalence of motors having 1.15SF, the 125% is what is built-in to the relay design.

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msamad
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#3

Re: Overload Setting

04/27/2011 10:26 PM

These threads also help:

http://cr4.globalspec.com/thread/57643/3-Phase-Overload-Setting

http://cr4.globalspec.com/thread/60385/Over-Load-and-Over-Current

- MS

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hien.nguyenquoc
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#4
In reply to #3

Re: Overload Setting

04/28/2011 1:22 AM

Most of answers are correct. But it also depends on the application. Some have to set the OL current to 175%.

I have read one manual which I found it was a good guidance especially for small motor application. You set the current at 125% then start up the motor, reduce the setting and restart the motor until it is tripped. Then, try to set it one level higher at the trip point.

By doing this, it will give us a higher safety margin for the motor against OL protection.

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TonyS
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#5
In reply to #4

Re: Overload Setting

04/28/2011 3:56 AM

OK if you can load the motor 100% for your trials. Not really a practical solution.

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brich
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#6

Re: Overload Setting

04/28/2011 8:20 AM

it really depends.... with the motors I use, I wait until the RC (running current) is settled then set the O/L to 115% of RC. However if your motor is 100% loaded you can either set it to 115% or 120% of the NPA (name plate amps).. again educated decision.

Remember the overload is there to protect the motor and equipment.. be careful when making these decisions.

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