I apologize for the amount of questions here recently however I cant help but to learn from the experts here on this forumn. :grin:
This question deals with the different class overloads in a conventional starter. I know the standard for most bi-metal overloads for most applications is a class 20 overload, although others are avaliable upon request.
I am now working with the AB E3+ solid stage relay, and there are several different overload classes avaliable for this relay with just the click of a mouse. So I wanted to get a better understanding of where the different classes were applicable and what effect they have on the protection of the motor.
I understand that a class 20 overload relay is the most common class setting, and that by definition the relay will allow 6x the relay full load setting for 20 seconds. For each of the other classes wheather it be 10, 30, etc... this same 6x current value will be allowed to persist for a time indicated by the class of the relay. I also notice that with this E3 relay, the class setting will also determine how quickly the thermal model of the relay will decay after the motor is running or has been stopped. I believe the higher the class setting, the quicker the thermal model will decay, unless I have it backwards?
So with all that being said, I was wondering where it would be applicable to bump a standard class 20 overload to a class 30. On application I was aware of were for loads that were hard to start such as fans which took a while to get up to speed. There may be others, but the general rule of thumb seems to be for these motors that take long to get up to speed. By implementing a higher class however, are we risking damage to the motor by allowing higher currents to operate for a longer time during steady state condition when the motor is running?
On a somewhat seperate note, I notice that NEC allows overloads to be rated at 125% of FLA for motors that have a 1.15 service factor. It is my understanding that the bi-metal overloads from manufacturers charts already have this 125% built in so when selecting you should select the range that is applicable for the motor full load without any adjustment to the numbers. What about setting these solid state overload relays? If the motor has a 1.15 S.F. should you enter just the FLA assuming the relay accounts for this factor or do you need to adjust this current setting for the S.F.?
This question deals with the different class overloads in a conventional starter. I know the standard for most bi-metal overloads for most applications is a class 20 overload, although others are avaliable upon request.
I am now working with the AB E3+ solid stage relay, and there are several different overload classes avaliable for this relay with just the click of a mouse. So I wanted to get a better understanding of where the different classes were applicable and what effect they have on the protection of the motor.
I understand that a class 20 overload relay is the most common class setting, and that by definition the relay will allow 6x the relay full load setting for 20 seconds. For each of the other classes wheather it be 10, 30, etc... this same 6x current value will be allowed to persist for a time indicated by the class of the relay. I also notice that with this E3 relay, the class setting will also determine how quickly the thermal model of the relay will decay after the motor is running or has been stopped. I believe the higher the class setting, the quicker the thermal model will decay, unless I have it backwards?
So with all that being said, I was wondering where it would be applicable to bump a standard class 20 overload to a class 30. On application I was aware of were for loads that were hard to start such as fans which took a while to get up to speed. There may be others, but the general rule of thumb seems to be for these motors that take long to get up to speed. By implementing a higher class however, are we risking damage to the motor by allowing higher currents to operate for a longer time during steady state condition when the motor is running?
On a somewhat seperate note, I notice that NEC allows overloads to be rated at 125% of FLA for motors that have a 1.15 service factor. It is my understanding that the bi-metal overloads from manufacturers charts already have this 125% built in so when selecting you should select the range that is applicable for the motor full load without any adjustment to the numbers. What about setting these solid state overload relays? If the motor has a 1.15 S.F. should you enter just the FLA assuming the relay accounts for this factor or do you need to adjust this current setting for the S.F.?