# NEMA 2 starter sizing



## frenchelectrican (Mar 15, 2007)

460 Delta said:


> At what point or time did manufacturers derate size 2’s to 10hp on a 200 volt system? I’ve some Citations that are 15hp and maybe newer ones that derate them to 10hp, it’s something that I’ve noticed in the last few years and I’m wondering why and when.


If I remember correct it was on the borderline on limit rating on contractors and it been that way for last 15 years or so 

If ran on 230 volts then 15 Hp will work just fine on size 2 starter without much issue. 

with air compressor 15 HP at 200 volt system could take size two starter but right on the limit of rating so typically I go with size 3 or 2 1/2 if I can find it. 

Just dont mention IEC stuff that is worst than NEMA verison is.


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## micromind (Aug 11, 2007)

I don't know when they changed the ratings but I do know this.....the HP ratings of NEMA starters make no sense at all to me.


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## bill39 (Sep 4, 2009)

micromind said:


> I don't know when they changed the ratings but I do know this.....the HP ratings of NEMA starters make no sense at all to me.


Just curious: do you think NEMA ratings are too conservative?

It’s not something I ever put much thought into. Kinda like fighting city hall, you can’t win.


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## 460 Delta (May 9, 2018)

micromind said:


> I don't know when they changed the ratings but I do know this.....the HP ratings of NEMA starters make no sense at all to me.


What part makes no sense? I always thought it was a simple intuitive system made for us front line electricians. 
I suppose my question was when and why did they get more conservative on their ratings? 
I understand that 200 volt motors pull more current, but I didn’t think it would make a derate necessary.


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## micromind (Aug 11, 2007)

It's the HP ratings vs. the max current ratings. 

For example, a size 4 is good for 50HP @230 volts, 100 HP @ 460 volts and 135 amps. This makes sense

A size 1 however is good for 7 1/2 HP @ 230 but only 10 HP @ 460. It can handle 27 amps. Why not 15 HP @ 460. This doesn't make any sense at all. A 15 HP motor on 460 volts draws a lot less that 27 amps. It's even good for 7 1/2 HP @ 200 volts. Why only 10 HP @ 460?


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## 460 Delta (May 9, 2018)

micromind said:


> It's the HP ratings vs. the max current ratings.
> 
> For example, a size 4 is good for 50HP @230 volts, 100 HP @ 460 volts and 135 amps. This makes sense
> 
> A size 1 however is good for 7 1/2 HP @ 230 but only 10 HP @ 460. It can handle 27 amps. Why not 15 HP @ 460. This doesn't make any sense at all. A 15 HP motor on 460 volts draws a lot less that 27 amps. It's even good for 7 1/2 HP @ 200 volts. Why only 10 HP @ 460?


I was always told [true or not] it was because the arc is harder to interrupt at higher voltages and the lower current [lower hp] was necessary to make it possible.
I always had the same thoughts as a younger man, but the explanation made sense in that opening the contacts on a fully loaded 15hp motor on a 460 volt system would tax the abilities of a size 1 to quench the arc.
With the larger sizes, I suppose the arc quench is there because at that size people aren't after compactness, or weight reduction, just function.


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## frenchelectrican (Mar 15, 2007)

460 Delta said:


> I was always told [true or not] it was because the arc is harder to interrupt at higher voltages and the lower current [lower hp] was necessary to make it possible.
> I always had the same thoughts as a younger man, but the explanation made sense in that opening the contacts on a fully loaded 15hp motor on a 460 volt system would tax the abilities of a size 1 to quench the arc.
> With the larger sizes, I suppose the arc quench is there because at that size people aren't after compactness, or weight reduction, just function.


That what I heard and confirm that part espceally with smaller units the issue is arc surpession that is the key issue but being on 200 volts that kinda puzzle me a little.


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