On a Tesys T, if the application service factor is greater than 1.15, is there an approved method of allowing the extra current?


30 September 2021

Service factor greater then 1.15. Any approved methods of programming for this additional FLA   

Product Line:
LTMR solid state overloads

There is not a setting in the TeSys T to set a specific service factor.

Our advice is to set FLC1 to the nameplate FLA of the motor, some motors also list the service factor FLA.

The FLC1 setting should not be set above nameplate FLA. Motors are not intended to be run continuously at the service factor, it is a temporary state to allow the motor to work thru a brief overload condition.

Here is a quote from http://electrical-engineering-portal.com/motor-service-factor-sf-defined-by-nema

"For example, the standard SF for open drip-proof (ODP) motors is 1.15. This means that a 10-hp motor with a 1.15 SF could provide 11.5 hp when required for short-term use. Some fractional horsepower motors have higher service factors, such as 1.25, 1.35, and even 1.50.

NEMA defines service factor as a multiplier, when applied to the rated horsepower, indicates a permissible horsepower loading, which may be carried under the conditions specified for the service factor at rated voltage and frequency.
This service factor can be used for the following:

To accommodate inaccuracy in predicting intermittent system horsepower needs.
To lengthen insulation life by lowering the winding temperature at rated load.
To handle intermittent or occasional overloads.
To allow occasionally for ambient above 40°C.
To compensate for low or unbalanced supply voltages.

NEMA does add some cautions, however, when discussing the service factor:

Operation at service factor load for extended periods will usually reduce the motor speed, life and efficiency.
Motors may not provide adequate starting and pull-out torques, and incorrect starter/overload sizing is possible. This in turn affects the overall life span of the motor.
Do not rely on the service factor capability to carry the load on a continuous basis.
The service factor was established for operation at rated voltage, frequency, ambient and sea level conditions."

The Tesys T trip point is already at 112% of FLC1 thus allowing some momentary overload. If the customer wishes to increase the setting for FLC1, they do so at their own peril.