motors in other than dwelling units

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tryin

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I am trying to remember this exact question, I maybe off a little and will require some guidance if at all possible. The question was for a 120/480 20 hp motor, it had a service factor of 1.15, it was a four wire wye. The question was how many amp feeder.

I have seen several of these and I do get them confused when It comes to re asking about them for help. They have even thrown in a code letter of "F" in some of them.

I need help and I'm not even smart enough to recall the exact question. This last time I used the 20 amps, went to the motor HP chart and chose the factor for the 20 hp motor and forgot about the other facors in the question. That factor was one of the answers.

There are four motor questions on this test that deal with motors other dwelling units, and I can't get any of them right. Can some body simplify the formulas for me?
 
If you just fax us the tests we will take them for you. :wink:

You gotta try and put forth some effort on your part here.
 
Bob

Bob

I don't want the answers, I want to know what to use to get them. The plan review test I am taking does not have any plans to review. every motor example I have ever seen dealt with voltage drop, of which is not a factor for these questions. I have no examples, no formulas nothing useful. It's not a secret decoding process, I just want to know what to do to get feeder ampacities for 4 wire wye connected 3 phase motors. I have been watching this site for years, I know you guys don't take tests for people, Thats not what I want. I have passed all my commercial and res exams the first shot, I can't do this one. I'm frustrated.
 
I am not exactly sure what you are looking for. Table 430.250 will give you the amp. of a motor that is 20 hp at 460 volts. The power factor is mentioned at the end of the table with an asterik
 
Does one ever connect the system neutral to a 3-ph motor? :-?

I'm thinking of the never-connect-the-neutral-to-a-primary rule.
 
Thanks, Dennis. What I am looking for is formulas to obtain the proper ampacities for motor questions. All I need is to be shown HOW to get KVA'S when parts of your equation is missing or how to get VA or Watts or KW when parts of your equation is missing, or is 1.732 a "constant" factor when calculating 3 phase motors. While this is basic and mundane to those of you who do this every single day, It' like Japanese arithmatic to those of us who do not. I have read steel diagrams to box culverts that were easier decipher than this stuff.
 
You proof for a given equation, because other factors might or might not be involved (or presented) with the aspect of a sudo complex motor, does it or doesn't it matter to your appliable point of service ?
Trick question, yes, no... Service factor and power factor are to different things, an understanding of all of a motor(s) potentional aspects need to be well understood to understand what your reaching for!

Motors are just a different! Address accordingly!
 
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120/480 motor

120/480 motor

120/480 never heard of a 120/480 motor.
 
Correct me if I am wrong, your looking the the Ip (Phase ampere's) of the motor?

There are a quite a few formula's that you can use.

Eg. VA= P/PF, VA= E*I, Ip= El/1.723 , In a Wye Connection, The phase current and the line current are the same.

Convert the Hp to Watts, then use ohms law to figure Z, I, VA , PF etc.

1.732 is a constant when using 3 phase, this enable you to compute each phase depending on the question at hand.

As stated above not sure what your looking for, be more convient if you can find a suitable question asking for specific info.

--------------------------------------------------------------------------domnic

120/480 never heard of a 120/480 motor.

I do believe that was the motor that was used to test the Warp drive on the 1st Enterprise




cadpoint said:
Trick question, yes, no... Service factor and power factor are to different things,
Click to expand...

Service factor is the percentage of how often you have to have the unit put in a shop, and Power Factor is the HOW MUCH it going to cost :roll:



~FYE~
 
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Strictly speaking you do not really size a motor feeder from the info on the nameplate.

As Dennis mentioned you need to get that info from the tables in Article 430.
 
LarryFine said:
Does one ever connect the system neutral to a 3-ph motor? :-?

I'm thinking of the never-connect-the-neutral-to-a-primary rule.
Click to expand...
Larry,
I have seen a couple of larger (300 hp+) motors that had a T0 connection point, but we did not use it. I have no idea as to its purpose.
 
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