# Cletus Question......NEMA Starters



## micromind (Aug 11, 2007)

First, a bit of background.....long ago, there was a member here who went by 'Cletus'. He would often ask questions, a lot of which were idiotic to the point you'd just shake your head. Occasionally though, he would ask one that actually made you think a bit.

Here's mine......you decide if it's totally dumb or actually worthwhile.....lol.

A size 1 NEMA starter is rated at 7.5 HP @ 230 volts. It is also rated at 10 HP @ 460 volts. Further, it is rated @ 27 amps continuous. I don't know about any others but the Allen Bradley 509 is rated at 288 inrush amps. 

It seems to me that this starter could easily handle a 15 HP motor @ 460 volts. Why is it rated for 10 HP?

I've seen more than a dozen size 1 starters controlling 15 HP motors, most of them have been in service for a long time. I've yet to see a problem of any sort. 

Is NEMA stupid .......or are their ratings politically motivated, even way back then? 

Same thing goes for a size 2. 15 HP @ 230 volts and 25 HP @ 460 volts. Why not 30 HP? 

Even a size 3.....30 and 50 HP. Why not 60?

The 460 volt rating on size 4 and higher is 2X the 230 volt rating. This makes sense, the smaller sizes don't. Further, on the size 4 and higher, the full-load current of the motor is closer to the maximum continuous current of the starter than the smaller sizes, even after bumping it up a notch. 

Other than marking and code [430.83(A)(1)] is there an actual reason for the lower 460 volt HP ratings?


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## drsparky (Nov 13, 2008)

Your correct, it is a Cletus question.


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## Peewee0413 (Oct 18, 2012)

micromind said:


> First, a bit of background.....long ago, there was a member here who went by 'Cletus'. He would often ask questions, a lot of which were idiotic to the point you'd just shake your head. Occasionally though, he would ask one that actually made you think a bit.
> 
> Here's mine......you decide if it's totally dumb or actually worthwhile.....lol.
> 
> ...


Arc Break/Arc Make......?

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## frenchelectrican (Mar 15, 2007)

micromind said:


> First, a bit of background.....long ago, there was a member here who went by 'Cletus'. He would often ask questions, a lot of which were idiotic to the point you'd just shake your head. Occasionally though, he would ask one that actually made you think a bit.
> 
> Here's mine......you decide if it's totally dumb or actually worthwhile.....lol.
> 
> ...



Here is the Cletus Answer .,

anytime you double the voltage the arc on concat gap will increase and can do some more wear and tear.

the other issue is the AIC rating on higher voltage also may play in this too.

that why I am thinking they are converseally rated for 400 volts and up.


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## macmikeman (Jan 23, 2007)

I wonder if you could buy an Ebay while your at EBay?...........


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## Switched (Dec 23, 2012)

You didn't do it right... 

Can I do dis?


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## paulengr (Oct 8, 2017)

The continuous rating is what matters. Don’t forget two things though. First, modern energy efficient motors are a lot lower FLA so you can somewhat push things. That’s why IEC is much better...it considers duty, AIC, X/R and other factors so you “oversize” as needed unlike the NEMA one size fits all approach.

Second difference is some loads have high starting torque like compressors so there it is very common to see “undersized” starters. For instance a.150 HP motor on a 100 HP load. The load is 100 HP and the overload relay is set for that but the fuses/breaker are oversized.


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## tates1882 (Sep 3, 2010)

Old Cletus, a pretty good pot stirrer! Rather lively forum back then. 

My vote is being to withstand closing into a fault at 15, 30, 60 hp and still being able to function. 

Happy New year


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## paulengr (Oct 8, 2017)

Here is right from the horses mouth:

https://www.nema.org/standards/pages/Controllers-Contactors-and-Overload-Relays-Rated-600-V.aspx

NEMA contactors are NOT AIC rated...that’s the job of the fuses/MCP/breaker. They are rated to interrupt overloads, generally up to 10 times FLC but the actual tables are basically stall current which is around 6 times FLC. There is a “setvice limit” current larger than the rated continuous current too and they are tested down to 0.5 PF. So there is some wiggle room here but oversuzing motors has a lot of variables. Since these days most contactors are actually IEC using IEC rating systems would be prudent whether it carries a NEMA rating or not.


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## chicken steve (Mar 22, 2011)

paulengr said:


> Here is right from the horses mouth:
> 
> https://www.nema.org/standards/pages/Controllers-Contactors-and-Overload-Relays-Rated-600-V.aspx
> 
> ...


Good one Paul, but a _lot_ to digest. 

Can this be reduced to the simplicity of _definite_ purpose *VS* _general_ use contactors?

here's a nema bulletin i found, but it's not quite declaring a dif....:001_huh:~CS~


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## HackWork (Oct 2, 2009)

chicken steve said:


> Good one Paul, but a _lot_ to digest.
> 
> Can this be reduced to the simplicity of _definite_ purpose *VS* _general_ use contactors?
> 
> here's a nema bulletin[/ur] i found, but it's not quite declaring a dif....:001_huh:~CS~




Steven, it was already explained to you a few times that definite purpose contactors are only a designation for recognized units that are part of a larger listed assembly. 

That was another issue that you were wrong about, it was clarified for you, you ignored it and refused to recognize it, and then you went on to say the same incorrect thing again. Much like the GEC thing.

I wish you would stop doing this.


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## JRaef (Mar 23, 2009)

The reason for the difference in NEMA Size 1 230V vs 460V ratings is indeed what French said. It's because of the arc on opening the contactor under the worst case scenario; motor fully loaded at Service Factor Amps and .7 power factor. The arc will contain more thermal energy at 480V motor than at 240V with the same amps. NEMA ratings have to account for inching and plugging duty, basically the worst thing you can throw at it under the worst conditions with the worst possible motor connected to it. 

History lesson time;
The entire concept of NEMA ratings was to AVOID having to get an EE involved in every single application, so an electrician can safely apply a NENA starter to any motor in any common application within the HP limits defined by NEMA. This was driven by the Automotive industry back in the 50s as model year production lines changed fast, so next year's line was being built while the current year was in production, using machinery and equipment, like starters, scavenged from the previous model. The Automotives did not want to hire more "ivory tower" EEs to make every decision, they wanted line electricians to be able to do it without worrying about whether the starter would survive. So the NEMA sizing system looked at the 90% of applications from a worst case scenario, then everything less than that was going to be overkill, but there was nothing wrong with that from an economic standpoint (at that time). 

Meanwhile in post WWII Europe, our Marshal Plan to rebuild the EU economies provided education programs that ended up churning out a LOT of engineers, but "tradesmen" were few and far between. That's because many had been killed in the war and their kids saw that the uneducated were used as cannon fodder in two successive wars, so they opted to take the education path. The result was a glut of EEs and a shortage of electricians in the 50s. So IEC rules on component selection were based on an EE making decisions about appropriate use of precious resources, like silver for contacts, by calculating EXACTLY how much was needed for an EXACT application that would be expected to last an EXACT length of time, then DISCARDED. The last part was because with a shortage of tradesmen, there was no time to fix something like a contactor, you just tossed it and replaced it with new. They were made to be replaced FAST (hence DIN rail, crimp sleeves etc.) so the electricians could move on to the next task. That same concept here in the US is what became knows as "Definite Purpose", but was even more exacting because it mostly had to do with parts just outlasting warranties. 

In the 70s and 80s when our economy started cooling down, people started rethinking that economic issue of NEMA as bean counters (accountants) began penny pinching everything, and IEC looked more enticing to them. But we also lacked the attention to detail it required and a LOT if people misapplied them, leading to a lot of failures. Over time though, people have learned how to properly apply them. 

Here's what I came up with for a class I used to teach on motor controls:
NEMA = *N*o *E*lectrician *M*akes *A*ppologies
IEC = *I*'ve *E*xamined *C*arefully
DP = *D*on't *P*urchase.


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## macmikeman (Jan 23, 2007)

JRaef said:


> The reason for the difference in NEMA Size 1 230V vs 460V ratings is indeed what French said. It's because of the arc on opening the contactor under the worst case scenario; motor fully loaded at Service Factor Amps and .7 power factor. The arc will contain more thermal energy at 480V motor than at 240V with the same amps. NEMA ratings have to account for inching and plugging duty, basically the worst thing you can throw at it under the worst conditions with the worst possible motor connected to it.
> 
> History lesson time;
> The entire concept of NEMA ratings was to AVOID having to get an EE involved in every single application, so an electrician can safely apply a NENA starter to any motor in any common application within the HP limits defined by NEMA. This was driven by the Automotive industry back in the 50s as model year production lines changed fast, so next year's line was being built while the current year was in production, using machinery and equipment, like starters, scavenged from the previous model. The Automotives did not want to hire more "ivory tower" EEs to make every decision, they wanted line electricians to be able to do it without worrying about whether the starter would survive. So the NEMA sizing system looked at the 90% of applications from a worst case scenario, then everything less than that was going to be overkill, but there was nothing wrong with that from an economic standpoint (at that time).
> ...


Thank you, this was very interesting and well written. I wish Telsa would write his history lessons so concisely.


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## p.imbeault (Nov 27, 2014)

JRaef said:


> The reason for the difference in NEMA Size 1 230V vs 460V ratings is indeed what French said. It's because of the arc on opening the contactor under the worst case scenario; motor fully loaded at Service Factor Amps and .7 power factor. The arc will contain more thermal energy at 480V motor than at 240V with the same amps. NEMA ratings have to account for inching and plugging duty, basically the worst thing you can throw at it under the worst conditions with the worst possible motor connected to it.
> 
> History lesson time;
> The entire concept of NEMA ratings was to AVOID having to get an EE involved in every single application, so an electrician can safely apply a NENA starter to any motor in any common application within the HP limits defined by NEMA. This was driven by the Automotive industry back in the 50s as model year production lines changed fast, so next year's line was being built while the current year was in production, using machinery and equipment, like starters, scavenged from the previous model. The Automotives did not want to hire more "ivory tower" EEs to make every decision, they wanted line electricians to be able to do it without worrying about whether the starter would survive. So the NEMA sizing system looked at the 90% of applications from a worst case scenario, then everything less than that was going to be overkill, but there was nothing wrong with that from an economic standpoint (at that time).
> ...


That's a great little history lesson!

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## telsa (May 22, 2015)

macmikeman said:


> Thank you, this was very interesting and well written. I wish Telsa would write his history lessons so concisely.


Me too. :thumbsup:


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## Peewee0413 (Oct 18, 2012)

JRaef said:


> The reason for the difference in NEMA Size 1 230V vs 460V ratings is indeed what French said. It's because of the arc on opening the contactor under the worst case scenario; motor fully loaded at Service Factor Amps and .7 power factor. The arc will contain more thermal energy at 480V motor than at 240V with the same amps. NEMA ratings have to account for inching and plugging duty, basically the worst thing you can throw at it under the worst conditions with the worst possible motor connected to it.
> 
> History lesson time;
> The entire concept of NEMA ratings was to AVOID having to get an EE involved in every single application, so an electrician can safely apply a NENA starter to any motor in any common application within the HP limits defined by NEMA. This was driven by the Automotive industry back in the 50s as model year production lines changed fast, so next year's line was being built while the current year was in production, using machinery and equipment, like starters, scavenged from the previous model. The Automotives did not want to hire more "ivory tower" EEs to make every decision, they wanted line electricians to be able to do it without worrying about whether the starter would survive. So the NEMA sizing system looked at the 90% of applications from a worst case scenario, then everything less than that was going to be overkill, but there was nothing wrong with that from an economic standpoint (at that time).
> ...


Bravo  

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## paulengr (Oct 8, 2017)

chicken steve said:


> Good one Paul, but a _lot_ to digest.
> 
> Can this be reduced to the simplicity of _definite_ purpose *VS* _general_ use contactors?
> 
> here's a nema bulletin i found, but it's not quite declaring a dif....:001_huh:~CS~


NOT really.

If you read the documentation on definite purpose especially inductive ratings even when used as a panel builder except for lighting contractors and even then, with NO magnetic ballasts, and even if I'm an EE, I can't see a practical way to use them. By the time you derate for an application you end up at NEMA or IEC anyways and the money you "saved" evaporated.

DP = Dumb Purchasing?

This is like the purchasing idiot I once knew that switched all the bearings out for unground bearings to save money. Yes, you can buy those but I have no idea where they could possibly have a legitimate use. This was not done in a cheap ass fly by night operation. It was the largest site with thousands of employees in a Fortune 100 company. This is why as ridiculous as it sounds most of the automotives have engineers write specs for purchasing to follow and electricians order from an in house "catalog" put out by purchasing. Might explain why purchasing all wear Rolexes too. In defense of buyers, some of them are so stupid they can't even figure out how to get perks like Rolex watches.

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## JRaef (Mar 23, 2009)

In a lot of organizations, buyers are incentivized (with bonuses) to reduce costs every year by xx%. These programs typically have little to no input from Engineering or Maintenance or if there is, it is often ignored because Purchasing has no accountability for increased repairs or maintenance costs, just the cost of goods. It's a very flawed system in my opinion, but I know people who are members of a large nationwide association of purchasing professionals who staunchly defend the practice.


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## sparkiez (Aug 1, 2015)

JRaef said:


> In a lot of organizations, buyers are incentivized (with bonuses) to reduce costs every year by xx%. These programs typically have little to no input from Engineering or Maintenance or if there is, it is often ignored because Purchasing has no accountability for increased repairs or maintenance costs, just the cost of goods. It's a very flawed system in my opinion, but I know people who are members of a large nationwide association of purchasing professionals who staunchly defend the practice.


I have dealt with this personally. Cutting cost does not equate to eliminating waste. Heck, if you keep the fat properly trimmed, your costs will increase because your company has a higher marketshare.


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## nolabama (Oct 3, 2007)

I hated to see ole Cletus go .... 

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