Non-Standard HP Motor FLA

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CompositionB

Member
Location
Tucson, AZ
I am working on a project in a city that still uses the 1996 NEC.

Article 430-6(a) requires the full load current listed in the tables to be used instead of the full load current shown on a motor's nameplate. One of the motors on this project is rated 35 HP, 42 FLA, 480V, 3?.

Since 35 HP is not listed in the table I cannot comply with 430-6(a). What should be done in this case?

Thanks in advance,

Kris
 

John Valdes

Senior Member
Location
SC.
Occupation
Retired Electrician
I just read the article and see your question loud and clear. I don't know the answer. But this brings up another situation regarding metric motors. When you convert kw to hp you never get a standard hp rating, close but not exact. So I further ask, how can anyone comply with 430-6(a) if they are dealing with metric motors or special built motors.

Note: I just looked at the conversion from kw to Hp in a motor catalog. They are rounding up or down to the nearest hp value. How are you guys addressing this inconsistency?

I would use nameplate as I have always done. Am I doing this wrong?
 
I just read the article and see your question loud and clear. I don't know the answer. But this brings up another situation regarding metric motors. When you convert kw to hp you never get a standard hp rating, close but not exact. So I further ask, how can anyone comply with 430-6(a) if they are dealing with metric motors or special built motors.

Note: I just looked at the conversion from kw to Hp in a motor catalog. They are rounding up or down to the nearest hp value. How are you guys addressing this inconsistency?

I would use nameplate as I have always done. Am I doing this wrong?

430.6 Ampacity and Motor Rating Determination.
(A)(1) ........Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary.

Having said that, does the motor have a NRTL listing? The AHJ may have a problem with it if it is a non-recognizable electrical equipment.

IMO, just pick the next highest horsepower or amperes.
 

CompositionB

Member
Location
Tucson, AZ
The client just informed me that there will be a second 35 HP motor. The ratings on that motor's nameplate are 35.4 HP, 43.1 A, so this same issue applies to that motor as well.

I'm not sure what 430.6(A)(1) has to do with NRTL listing of the equipment or how listing is relevant. Is there a code section that prohibits connecting power to a non-listed piece of utilization equipment?

I am going to try to get in touch with the local AHJ regarding non-standard HP motors. I'll post what I find out from them FYI.

Kris
 

John Valdes

Senior Member
Location
SC.
Occupation
Retired Electrician
In this case I would look at the motor as 40 hp and use the current values listed for 40 hp. Thats what I would do.
 

CompositionB

Member
Location
Tucson, AZ
In this case I would look at the motor as 40 hp and use the current values listed for 40 hp. Thats what I would do.

That was what I initially considered doing but then I realized that in the case of short circuit protection sizing the most conservative assumption is to round the motor down to a 30 HP.

But, for the purposes of conductor sizing and load calculations the 40 HP current would be most conservative. So, should I use the 30 HP current for SCPD sizing and the 40 HP current for everything else?

I'm still waiting for the AHJ to respond to my email.

Kris
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
Motors do not carry a thrid party lable as the same motor could be used in many applications such as in an A/C or as a pool motor or what not. At least that's the story I got from UL.

As for sizing I would go with the FLA and leave it at that.
 
Motors do not carry a thrid party lable as the same motor could be used in many applications such as in an A/C or as a pool motor or what not. At least that's the story I got from UL.

As for sizing I would go with the FLA and leave it at that.

In our industrial applications motors do have CSA labels as well as the UL mark shows up often. These are not labeled for Art. 500 locations, whhich always have the specific UL approval for that purpose. On the other hand we do buy IEEE-841 motors in most cases.

So my question would be, what governs the manufacturing of the motors besides NEMA 1 and what assurances the buyer/user have that the motors is manufactured to that Standard and more importantly that it is safe to operate?
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
In our industrial applications motors do have CSA labels as well as the UL mark shows up often. These are not labeled for Art. 500 locations, whhich always have the specific UL approval for that purpose. On the other hand we do buy IEEE-841 motors in most cases.

So my question would be, what governs the manufacturing of the motors besides NEMA 1 and what assurances the buyer/user have that the motors is manufactured to that Standard and more importantly that it is safe to operate?

To be perfectly honest, I don't know. If I remember, I'll ask our UL rep at the next IAEI meeting I attend.
 

cschmid

Senior Member
I am working on a project in a city that still uses the 1996 NEC.

Article 430-6(a) requires the full load current listed in the tables to be used instead of the full load current shown on a motor's nameplate. One of the motors on this project is rated 35 HP, 42 FLA, 480V, 3?.

Since 35 HP is not listed in the table I cannot comply with 430-6(a). What should be done in this case?

Thanks in advance,

Kris


[/QUOTE] Most electrical equipment is rated in volt-amperes (VA) or watt input. Basic to the understanding of Article 430 is the fact that motors traditionally have been rated in horsepower output. Circuits supplying motors are sized according to the input to the motor. The input includes the motor losses and the power factor of the motor. The losses are not the type of information found on the nameplate of a motor. Tables 430.249 and 430.250 contain accurate industrywide input ampere ratings for motors.
However, some motors are available with their output ratings expressed in watts and kilowatts. (One horsepower equals approximately 746 watts.) It is important to understand that circuits that supply motors not rated in horsepower still must be sized according to the input of the motor, rated in amperes. Sizing circuits based solely on kilowatt output results in seriously undersized conductors (because the current requirements of the losses and the power factor are neglected) and the improper application of overcurrent devices. See 430.6 for ampacity and motor rating determination.
[/QUOTE]

this is out of the 2008..
 
Most electrical equipment is rated in volt-amperes (VA) or watt input. Basic to the understanding of Article 430 is the fact that motors traditionally have been rated in horsepower output. Circuits supplying motors are sized according to the input to the motor. The input includes the motor losses and the power factor of the motor. The losses are not the type of information found on the nameplate of a motor. Tables 430.249 and 430.250 contain accurate industrywide input ampere ratings for motors.
However, some motors are available with their output ratings expressed in watts and kilowatts. (One horsepower equals approximately 746 watts.) It is important to understand that circuits that supply motors not rated in horsepower still must be sized according to the input of the motor, rated in amperes. Sizing circuits based solely on kilowatt output results in seriously undersized conductors (because the current requirements of the losses and the power factor are neglected) and the improper application of overcurrent devices. See 430.6 for ampacity and motor rating determination. [/quote]

this is out of the 2008..[/quote]

'Seriously'? A ridiculous unquantified statement. What is 'serious undersizing'? It usually means several times or an order of magnitude and I seriously:D doubt that would occur just because 'ignoring' the power factor and efficieny.
 

cschmid

Senior Member
Most electrical equipment is rated in volt-amperes (VA) or watt input. Basic to the understanding of Article 430 is the fact that motors traditionally have been rated in horsepower output. Circuits supplying motors are sized according to the input to the motor. The input includes the motor losses and the power factor of the motor. The losses are not the type of information found on the nameplate of a motor. Tables 430.249 and 430.250 contain accurate industrywide input ampere ratings for motors.
However, some motors are available with their output ratings expressed in watts and kilowatts. (One horsepower equals approximately 746 watts.) It is important to understand that circuits that supply motors not rated in horsepower still must be sized according to the input of the motor, rated in amperes. Sizing circuits based solely on kilowatt output results in seriously undersized conductors (because the current requirements of the losses and the power factor are neglected) and the improper application of overcurrent devices. See 430.6 for ampacity and motor rating determination.

this is out of the 2008..[/quote]

'Seriously'? A ridiculous unquantified statement. What is 'serious undersizing'? It usually means several times or an order of magnitude and I seriously:D doubt that would occur just because 'ignoring' the power factor and efficieny.[/QUOTE]

hey man just quoting what is in the 2008 I cut and pasted it..I would just use the FLA and rock and roll
 
hey man just quoting what is in the 2008 I cut and pasted it..I would just use the FLA and rock and roll

By no means did I criticise you or what you may have said. I presume that this is in the handbook, not in the actual Code.(I did a serach on the begginning 3 words and no match was found.) In that case the writers of the Handbook would better serve the community if they use technical terms that are quantified, not big, large or 'seriously oversized' but 10%, double or magnitude difference.
 
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