I have three (3) Phase 15 HP 208 Volt motors for the dryer fans in a car wash. I went by the name plate rating to size the feeder to the MCC Panel. Evidently by not using the table in 430.150 I sized the feeder too small. These fans come on when the car wash is done and the car exits to blow dry the car. Wouldnt these motors be considered intermittent duty or short time duty? If this is the case then I can size the feeders off table 430.22E. Write me back please. Thanks, Leamon
Motors
- Thread starter lrollo
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Re: Motors
Roger, am I not interpreting the code right in 430.24 when it tells me to use 430.6A which tells me to use the tables in 430.150 to rate my motor. This is a three Phase table. The exception in 430.24 tells me I still have to use 430.150 for the rating but if intermittent duty I can use the multiplier in table 430.22(e). Am I wrong in this?
Roger, am I not interpreting the code right in 430.24 when it tells me to use 430.6A which tells me to use the tables in 430.150 to rate my motor. This is a three Phase table. The exception in 430.24 tells me I still have to use 430.150 for the rating but if intermittent duty I can use the multiplier in table 430.22(e). Am I wrong in this?
Re: Motors
Irollo: I agree with your last statement. 430.24 Exception (1) says you can use 430.22(E) for more than one motor. I also think your application fits the footnote to table 430.22(E): "Any motor application shall be considered as continuous duty unless the nature ........"
Also, see the definition of "duty" in article 100.
I really don't understand table 430.22(E). It seems like for other than continuous duty, all the numbers in the table should be less than the 125% that 430.24 requires. But the table lists numbers like 140% or 150%.
Steve
Irollo: I agree with your last statement. 430.24 Exception (1) says you can use 430.22(E) for more than one motor. I also think your application fits the footnote to table 430.22(E): "Any motor application shall be considered as continuous duty unless the nature ........"
Also, see the definition of "duty" in article 100.
I really don't understand table 430.22(E). It seems like for other than continuous duty, all the numbers in the table should be less than the 125% that 430.24 requires. But the table lists numbers like 140% or 150%.
Steve
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Re: Motors
I think the code section 430.22(E) headings IE:5 minute,15minute,etc, refer to a motor that is NAMEPLATED with an intermittent duty cycle. The safe bet would be to use 125% + the sume of the other motors to determine current. under section 430.24 exception 3 the code allows for the scenario you describe if motors are interlocked to not be running at the same time. Then you could size the conductor for only for that load which runs simultaneously.That said then you would have only one runninig at once. In that case each individual motor would then have a conductor size of 125% of its nameplate rating but the feeder could be sized to 125% of the largest in the wash.
I think the code section 430.22(E) headings IE:5 minute,15minute,etc, refer to a motor that is NAMEPLATED with an intermittent duty cycle. The safe bet would be to use 125% + the sume of the other motors to determine current. under section 430.24 exception 3 the code allows for the scenario you describe if motors are interlocked to not be running at the same time. Then you could size the conductor for only for that load which runs simultaneously.That said then you would have only one runninig at once. In that case each individual motor would then have a conductor size of 125% of its nameplate rating but the feeder could be sized to 125% of the largest in the wash.
Re: Motors
Well, I presented my case to the inspector and he agreed with my findings. If he had disagreed, I would have asked him to look at 430.26 and make a decision based on jurisdictional authority and the fact that When an amp meter is put on the line side of the motor breaker it only pulls 75 amps. Also, the motors will never have any more load on them than they already hav e, and they only run 50 seconds every 5 minutes at the busiest time of the carwash, and it is a private carwash for the dealership only and the general public never gets to use it. I do thank all of you for your input. As much as I know about the code, I would never assume to know it all. Its nice to get the opinions of other knowledgable electricians.
Well, I presented my case to the inspector and he agreed with my findings. If he had disagreed, I would have asked him to look at 430.26 and make a decision based on jurisdictional authority and the fact that When an amp meter is put on the line side of the motor breaker it only pulls 75 amps. Also, the motors will never have any more load on them than they already hav e, and they only run 50 seconds every 5 minutes at the busiest time of the carwash, and it is a private carwash for the dealership only and the general public never gets to use it. I do thank all of you for your input. As much as I know about the code, I would never assume to know it all. Its nice to get the opinions of other knowledgable electricians.
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