RACA Journal April 2023 | Page 47

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S3 :

Runs for 2.5 minutes and then must cool down for 7.5 minutes

3 Ph 50 Hz : Motor operating with a 3-phase supply at 50 Hertz

Ins : E 80

This indicates the insulation materials running and maximum operating temperatures . A : 105 º C E : = 120 º C B : 130 º C H : = 180 º C F : 155 ° C

Therefore E 80 indicates a motor normally running at 80 ° C with a maximum operating temperature of 120˚C .

This information is important in motor section and application . Looking at your issue with circuit breakers , we need to understand that whilst all circuit breakers will trip when the load exceeds their rated amps some will trip instantly while others have a delay . There are different classes of circuit breaker referring in this instance to the curve ratings . Certain circuit breakers will allow excess current for a limited specified time to cater for higher amperage drawn – for example during motor start-up .

On the other hand , when a circuit breaker is used in conjunction with electronic circuitry a rapid or instantaneous response is required . Different suppliers use different symbols , numbers or letters when designating various curve ratings . A general example is as follows :

1

2

Curve 1 or 10 AC high in rush ( motor start ) Curve 2 Medium response ( mixed loads ) Curve 3 Short delay ( lights etc ) Curve 0 or P Instant response ( electronics )

When connecting a system to a Curve 0 or Curve P you may experience tripping , as when the motors start up their starting inrush current is high . When selecting a circuit breaker , attention should be given as to which curve rating would best suit your application . On the front of the circuit breaker you may find 20A - C2 , the C2 indicating a curve 2 circuit breaker . Check the breakers ’ manufacturer ' s specifications to determine the circuit breakers ’ suitability for your application .

1 and 2 : Example comparative curves .

Thank you , Riaan . I hope you will experience success with your compressor connections and circuit breaker issues .

Thank you for all for your interesting questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures . RACA