Size MOP for a sngle motor

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peterphamee said:
In a single 3ph motor connection, can I size the MOP by FLA X 2.25 ? It's understood MCA = FLA X 1.25
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If you are saying motor over load protection, that is sized 125% of FLA motor nameplate. Unless there are some exception that allows greater than that and I’m not aware of.
 
There are a lot of variables: Size motor, type motor, service factors,etc.
For overload devices see 430.32, for ground-fault-short circuit see 430.52
 
peterphamee said:
In a single 3ph motor connection, can I size the MOP by FLA X 2.25 ? It's understood MCA = FLA X 1.25
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MOP? I know I'm the silly Brit here but I don't recognise that term. But I'm sure it isn't what we called a Motorised Potentiometer,.........
 
On the Motor nameplate indicated 3p, 480V, 60Hz, 150A branch circuit breaker. Is this 150A branch circuit breaker is included 125% of FLA? an Electrical Engineer advise me to X 125% of 150A branch circuit breaker to size CB on the panel. Is he correct?
Besoeker3 said:
MOP? I know I'm the silly Brit here but I don't recognise that term. But I'm sure it isn't what we called a Motorised Potentiometer,.........
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Maximum overcurrent protection that uses in US
 
petersonra said:
Where did the 2.25 number come from?
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Copy from factory table of MCA and MOP

Table 1 – Traditional air conditioner Load Rating MCA Correction Factor MCA Rating MOP Correction Factor MOP Rating Compressor 1 34.3 125% 42.9 225% 77.2 Compressor 2 34.3 100% 34.3 100% 45.7 Fan Motor 1 13.4 100% 13.4 100% 13.4 Fan Motor 2 10.0 100% 10.0 100% 13.4 Fan Motor 3 10.0 100% 10.0 100% 13.4 Heater 1 25.0 125% 31.2 100% 34.2 Heater 2 12.5 100% 12.5 100% 17.1 Humidifier 12.0 0% 0 0% 0 Total - - 154.3 - 182.4 (175)
 
Dsg319 said:
If you are saying motor over load protection, that is sized 125% of FLA motor nameplate. Unless there are some exception that allows greater than that and I’m not aware of.
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How do you size MCA and MOP to multi motors. Let me do this if it is correct?
MCA= 1.25 (M1 FLA+M2 FLA+M3FLA)
MOP+ (2.25XM1 FLA (Largest) ) + M2 FLA +M3 FLA
Please check it out and let me know
 
peterphamee said:
Copy from factory table of MCA and MOP

Table 1 – Traditional air conditioner Load Rating MCA Correction Factor MCA Rating MOP Correction Factor MOP Rating
Compressor 1 34.3 125% 42.9 225% 77.2
Compressor 2 34.3 100% 34.3 100% 45.7
Fan Motor 1 13.4 100% 13.4 100% 13.4
Fan Motor 2 10.0 100% 10.0 100% 13.4
Fan Motor 3 10.0 100% 10.0 100% 13.4
Heater 1 25.0 125% 31.2 100% 34.2
Heater 2 12.5 100% 12.5 100% 17.1
Humidifier 12.0 0% 0 0% 0
Total - - 154.3 - 182.4 (175)
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This doesn't look like a single motor. It's difficult to follow but seems to suggest that you need a conductor with an ampacity of not less than 154.3, and a circuit breaker not greater than 175A.
 
Are you selecting for a single unit that has all these loads within? If so it should have a nameplate with MCA and MOP for the unit.

If you have a feeder supplying multiple individual loads, between art 430 and 440 there would be a method to calculate the minimum feeder ampacity needed and is provisions for potentially having higher than usual maximum overcurrent protection on said feeder in some cases, mostly to allow for starting the motor(s) and not to allow higher than needed ampacity ability.
 
kwired said:
Are you selecting for a single unit that has all these loads within? If so it should have a nameplate with MCA and MOP for the unit. ...
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That’s right. MOP is not something you would calculate in the field, MOP is a value calculated by the equipment mfr and put on the equipment nameplate so that you don’t have to do the more complex method kwired described.
 
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