This one bothers me. Technicians think the compressor RLA is the maximum current it will draw.
To see how that isn't true, first we need to found out what the RLA is. RLA is short for Rated Load Amperes, and it is a calculated value based off of the MCC. What's that? MCC stands for Maximum Continuous Current, and that is the amount of current needed to trip the compressor overload. So already, based on this, we can determine that the RLA is not a good measurement of how much current the compressor should be drawing.
To complicate matters, there are two ways of calculating the RLA from the MCC. Some manufacturers, like Danfoss, divide the MCC by 1.4 to determine the RLA. The NEC standard is MCC/1.56. Copeland, along with Carlyle, use MCC/1.4 for contactor selection and MCC/1.56 for wire and overcurrent protection sizing. Bitzer publishes both ratings, and they don't specify which one to use.
A much better way of determining maximum compressor current is by using the compressor's MOC (Maximum Operating Current) rating. As the name suggests, it is the maximum (or very close to the maximum) current the compressor will consume under normal operating conditions.
To find out how much current the compressor should be drawing, manufacturer's data is your best friend. Selection software, such as Danfoss Coolselector 2, or mobile apps, like Copeland Mobile, are your best friends, not just for figuring out how much current the compressor should use, but also for tons of other useful information about compressors.
I know I've been ranting, but I wanted to get this off my chest. Thank you for reading.
To see how that isn't true, first we need to found out what the RLA is. RLA is short for Rated Load Amperes, and it is a calculated value based off of the MCC. What's that? MCC stands for Maximum Continuous Current, and that is the amount of current needed to trip the compressor overload. So already, based on this, we can determine that the RLA is not a good measurement of how much current the compressor should be drawing.
To complicate matters, there are two ways of calculating the RLA from the MCC. Some manufacturers, like Danfoss, divide the MCC by 1.4 to determine the RLA. The NEC standard is MCC/1.56. Copeland, along with Carlyle, use MCC/1.4 for contactor selection and MCC/1.56 for wire and overcurrent protection sizing. Bitzer publishes both ratings, and they don't specify which one to use.
A much better way of determining maximum compressor current is by using the compressor's MOC (Maximum Operating Current) rating. As the name suggests, it is the maximum (or very close to the maximum) current the compressor will consume under normal operating conditions.
To find out how much current the compressor should be drawing, manufacturer's data is your best friend. Selection software, such as Danfoss Coolselector 2, or mobile apps, like Copeland Mobile, are your best friends, not just for figuring out how much current the compressor should use, but also for tons of other useful information about compressors.
I know I've been ranting, but I wanted to get this off my chest. Thank you for reading.
