What is the relevancy between the actual full load current value (test result) and the supposedly corresponding values from industry standards?

Question

I work on evaluating a motor problem. If I am given an actual current at 100% full load, how does an industry standard value become relevant?

I have an example to illustrate the point I am trying to make:

If I will buy a motor, one needs to evaluate two groups of things:

1) The motors ratings and whether or not they fit my need. 2) If the already existing system are or are not compatible in all aspects.

For the first group, let us just say that I tested the motor. It is perfect. It outputs the required torque.

For the second group, let us say that i had to make sure that my cables and protection devices are capable of handling the worst case circumstances.

Now, while I will have an advantage of using current values from industry standards in order to make sure that my second group evaluations are perfect, I do not see any relevancy between the actual current from the full load test and the theoretical full load current from the industry standards?

So, my questions:

1- What is the relevancy between the actual full load current (test result) and supposedly corresponding values from industry standards?

2- What is the advantage of this relevancy?

Answer 1

let us say that i had to make sure that my cables and protection devices are capable of handling the worst case circumstances

Cables and protection devices should be selected so that the original motor can be replaced by a motor that has the same power and speed rating as the original. In North America and, I believe, in much of the rest of the world, there are electrical codes that provide tables that specify currents to be used for cable selection for a range of voltage ratings and motor power ratings. Those tables have been developed based on industry standards. The tables are generally adequate for motors of the most common types and speeds. I believe they cover nominal speeds from 1000 to 3600 RPM and "normal" speed vs. torque characteristics. Lower speed motors and high slip motors may require larger cable.

In selecting a motor, it should not be necessary to be too concerned about actual full-load current or industry standards unless the motor has unusual performance requirements. You should be aware of the currents used by electrical codes to specify cable sizing. If a motor that is under consideration for purchase has full-load current exceeding that value, you should look more closely at the requirements. Determine if there is something about the performance requirements that causes the current to be higher than expected.