GaryS
Member
To address the Over Load setting issue.
Lets not confuse the Motor Overload with Short Circuit protection both are important and must be evaluated separately, each has there own function.
6 A OL on 4 A motor is high. Let’s look at the NEC code I think we can all agree that is the governing body on this.
Sizing for overload is important to avoid serious damage for electrical application such as motor starter, machinery or others electrical equipment.
According to NEC, The general requirement for overload sizing be set around 115% or 125% from full load ampere. We should setting the overload relay within this parameter to avoid electric motor from serious damage.
For calculation of overload sizing, It depend on the motor full load ampere current rating, The service factor and temperature for motor.
For motors rated 40EC with a Service Factor of 1.15 or greater, 125% of the motors FLA is used to calculate the maximum size device for overload protection.
For motors rated greater than 40 EC or unmarked, 115% of the motors FLA is used to calculate the maximum size device regardless of the motor’s Service Factor.
If use of the previous size rules results in the motor tripping off line during starting, the device can be increased to a maximum of 140% of the motors FLA. (This rule would apply to across the line starters only)
For short circuit protection on a VFD I always refer to the manual and use their recommendations.
I think we can agree that 6 amps is 150% of 4 amps so in all cases 6 amps would be too high.
With the new motor the service factor is 1.0 unless otherwise shown
4 X 1.15 = 4.6 so the correct settings that motor should be 4.6 amps
I have run into this many times people keep moving the OL and sometimes the Branch circuit protection up because they keep tripping and shutting off the motor. But without correcting the original load problem all you will do let the smoke out of the motor and have a very lengthy down time.
I could write pages on this I have had so many calls on motor problems just because somebody set the overload to high.
As I have said earlier I use the 75% load rule. It’s just my standard it works for me and has never let me down. I have equipment still in service for over 35 years. Everybody has their own opinion. The normal average load should never exceed 75% of the device ratings.
I come up with that many years ago when I first started in industry. The engineers in my local power company informed me that is their standard. The 75% applies to all components transformers, wiring, motor starters, power supplies and yes motors as well.
Mike if you are of a mind PM me we can get into more details about the problem.
Lets not confuse the Motor Overload with Short Circuit protection both are important and must be evaluated separately, each has there own function.
6 A OL on 4 A motor is high. Let’s look at the NEC code I think we can all agree that is the governing body on this.
Sizing for overload is important to avoid serious damage for electrical application such as motor starter, machinery or others electrical equipment.
According to NEC, The general requirement for overload sizing be set around 115% or 125% from full load ampere. We should setting the overload relay within this parameter to avoid electric motor from serious damage.
For calculation of overload sizing, It depend on the motor full load ampere current rating, The service factor and temperature for motor.
For motors rated 40EC with a Service Factor of 1.15 or greater, 125% of the motors FLA is used to calculate the maximum size device for overload protection.
For motors rated greater than 40 EC or unmarked, 115% of the motors FLA is used to calculate the maximum size device regardless of the motor’s Service Factor.
If use of the previous size rules results in the motor tripping off line during starting, the device can be increased to a maximum of 140% of the motors FLA. (This rule would apply to across the line starters only)
For short circuit protection on a VFD I always refer to the manual and use their recommendations.
I think we can agree that 6 amps is 150% of 4 amps so in all cases 6 amps would be too high.
With the new motor the service factor is 1.0 unless otherwise shown
4 X 1.15 = 4.6 so the correct settings that motor should be 4.6 amps
I have run into this many times people keep moving the OL and sometimes the Branch circuit protection up because they keep tripping and shutting off the motor. But without correcting the original load problem all you will do let the smoke out of the motor and have a very lengthy down time.
I could write pages on this I have had so many calls on motor problems just because somebody set the overload to high.
As I have said earlier I use the 75% load rule. It’s just my standard it works for me and has never let me down. I have equipment still in service for over 35 years. Everybody has their own opinion. The normal average load should never exceed 75% of the device ratings.
I come up with that many years ago when I first started in industry. The engineers in my local power company informed me that is their standard. The 75% applies to all components transformers, wiring, motor starters, power supplies and yes motors as well.
Mike if you are of a mind PM me we can get into more details about the problem.
