Exam Prep, check my Calculations Please.

[Windclaw]

Someone out there in "forum-Land" please check these answers.

Calculations for a 3 phase motor.

3phase
10 hp
230 v

In the beginning this is all the information I had!
So I calculated the following...
FLC: 28A
EFF 1.495
PF= .668
VA= 11.154kVA
FLA=225A
SF=115

CONDUCTOR SIZE #10
CONDUIT SIZE 3/4'
BRANCH CIRCUIT PROTECTION 70A (INVERSE TIME BREAKER)
FEEDER CONDUCTOR SIZE #10

FEEDER PROTECTION BREAKER 70a
OVERLOAD FUSES 30a

Someone outthere check these calculations (they are from an old training manual I have).

Thank you,
Bob

 

[Dennis Alwon]

Bob I am not much good at this but art. 430.250 states FLC is 28 amps for a 3 phase 10 hp 230 volt motor so that is correct.

Now I believe you have to run a circuit that is based on 125% of the FLC which is 35 amps. That would mean a #8 wire unless we use 240.4(G) then a #10 would be adequate.

Hopefully someone who knows what they are talking about can help. At least this will get bumped.

 

[Windclaw]

Thank you Dennis, Just trying to increase my calculation skills, but it is sometimes difficult with nobody to bounce things off of. Again thank you.... Bob

 

[chris kennedy]

Now I believe you have to run a circuit that is based on 125% of the FLC which is 35 amps.

Nice bump. Bob never stated continuous duty.

 

[Windclaw]

Sorry I never stated continious duty, however the orginial question did not state that either, I assumed it when doing calculations, (because it also did not state imtermitent duty either). Also the only given data in the orginal question was ..3 phase 230v and 10hp. I was hoping I had done everything right to finally get all the answers ask for. Since I have NO answer key for the ancient text, I was getting help to check my skills at motor calculations.

Thank you again...Bob

 

[raider1]

Lets assume continious duty motor.

So the tabulated ampacity of a 10 HP 230 volt 3 phase motor is 28 amps.

We apply 125% for continious duty and have an ampacity of 35 amps.

We find a conductor with an ampacity of 35 amps, a #10 copper conductor has an ampacity of 35 amps at 75 degrees C.

The motor branch circuit short circuit and ground fault protection can be sized at 250% of the tablated motor full load current (Inverse time circuit breaker, Table 430.52). This would be 70 amps.

The motor overload protection would be sized at 115% of the nameplate full load current. Since the question did not have a nameplate value I am using the tabulated value of 28 amps. This would be 32.2, but 30 amps would work.

Chris

 

[westernexplorer]

Raider,
Nice lay-out.....looks good to me.

Windclaw, you have to watch every word in the question.....They use plausable nonsense to trip you up.....

 

[Windclaw]

:grin: I know, Many of the questions I faced where like that, just like the diagram used for asking about seal offs for conduit passing under a class 1 div1 location. the attempt to confuse by having two of the conduit pass completely through so if all you do is count the ones at the point where they exit the building you will have too many.

Bob