Calc Help

[mstrlucky74]

have job were all they give is the motor symbol on the E drawing with the horeepower within the symbol. some of the motors show on the panel schedule. some questions. need guidance on sizing. FYI this is only budgetary for us.

1. for the motors that show on panel schedule they only show the breaker size and the kw[or maybe kva..cant remember] for the motors. so in this instance if i wanted to size the wire would i go off the motor hp,breaker size or kw/kva?

2. so i guess i need to know the answer to #1 for this question. when sizing a motor based on HP i believe i need to use the FLA based on NEC??

3. what is the NEC rule for when a disconnect/OCPD is needed next to the motor?

thanks a lot for the help on this.

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[Ingenieur]

1 would use the kva

2 use nec fla for sizing
use nameplate for setting ol's

3 doesn't have to be next to it (there are some exceptions like elevators)
can be remote but must be lockable
alot of times a design/cost decision

eg if a long walk from the cb or mcc local may be better
if close to the mcc, tha mcc cb may be better
there may be osha considerations depending on equipment

 

[mstrlucky74]

1 would use the kva

2 use nec fla for sizing
use nameplate for setting ol's

3 doesn't have to be next to it (there are some exceptions like elevators)
can be remote but must be lockable
alot of times a design/cost decision

eg if a long walk from the cb or mcc local may be better
if close to the mcc, tha mcc cb may be better
there may be osha considerations depending on equipment

thanks ..so when i have all 3[brkr size,kva and hp] what should i use to size the wire?

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[Ingenieur]

thanks ..so when i have all 3[brkr size,kva and hp] what should i use to size the wire?

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assuming all are for a motor load
hp (but compare it to calculated kva for a sanity check)
since estimating if a big difference use the larger
or rfi

 

[mstrlucky74]

so whats the code req. for the overcurrent device next to motor. thanks

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[kingpb]

motors are given in Hp (NEMA), or KW (IEC).

You need to use the NEC for amps

 

[drktmplr12]

so whats the code req. for the overcurrent device next to motor. thanks

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there is no code requirement for overcurrent device to be 'next to' the motor. the code requires that the over current device provide short circuit and thermal overload protection of the motor and conductors between the motor and the controller. with motors, this is often done with a motor circuit protector (circuit breaker with only an adjustable magnetic trip) and overloads (on the starter).

a disconnect is only required where the motor circuit protector is not lockable. it is designer/owner preference to place a disconnect next to the motor.

the conductors must be sized according to part II of article 430. Start with 430.21 (2011 NEC)

 

[Dale001289]

have job were all they give is the motor symbol on the E drawing with the horeepower within the symbol. some of the motors show on the panel schedule. some questions. need guidance on sizing. FYI this is only budgetary for us.

1. for the motors that show on panel schedule they only show the breaker size and the kw[or maybe kva..cant remember] for the motors. so in this instance if i wanted to size the wire would i go off the motor hp,breaker size or kw/kva?

2. so i guess i need to know the answer to #1 for this question. when sizing a motor based on HP i believe i need to use the FLA based on NEC??

3. what is the NEC rule for when a disconnect/OCPD is needed next to the motor?

thanks a lot for the help on this.

Sent from my SM-G955U using Tapatalk

The Disconnect/OCPD doesn't necessarily need to be next to the motor...however the Disconnect should be within sight of the controller (starter), see 430.102 for exceptions etc.
Full Load Current (FLC) shown in NEC tables is not the same as Full Load Amps (FLA) at the motor nameplate but can be used for sizing purposes (i.e. overloads 430.32) when motor FLA is not known.