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Old 12-04-2014, 09:13 PM   #1
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Default rule 28-200

can someone explain when you use rule 28-200 (d) (iii) of the 2012 CEC. 400% and 300%
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Old 12-04-2014, 09:35 PM   #2
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Default rule 28-200

Use those rules when you use a breaker with inverse time characteristics

"Thermal magnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions. The thermal portion of the circuit breaker provides an "inverse time" response feature, which trips the circuit breaker sooner for larger overcurrents but allows smaller overloads to persist for a longer time. On very large over-currents during a short-circuit, the magnetic element trips the circuit breaker with no intentional additional delay.[6]"
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Old 12-04-2014, 09:50 PM   #3
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thanks. I am looking at question and I cannot figure it out. "a motor generator arc welder is to be connected to a shop distribution panel feeder using R90 copper conductor. Primary current rating 60A duty cycle one hour. What is the max rating of circuit breaker required to protect the welder supply conductors.
The answer is 150 A but how do you get that answer??
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Old 12-05-2014, 09:28 AM   #4
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Rule #28-200 sends you to Table 29, which gives you 250% of FLA.

60x250%=150A

Rule #28-200(d) only applies if the motor won't start. Does the question stipulate that the motor won't start?
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