VFD on Non "Inverter Duty" Motor CIID1

[cowski]

A customer is trying to get me to wire up a non "inverter duty" motor in a Class II Div 1 (dust hazard) environment. The motor itself is rated for the hazardous area (it's just not inverter duty).

Do you know if this is a code violation? I wouldn't have a problem if it wasn't hazardous area... I've read that running a non inverter motor can cause heat problems, which concerns me given the dust hazard. But this motor should be sealed, so no fan right? But it would still generate more heat running at low / speed high toque and current, right?

It's a small 3/4 HP motor. The motor is pretty close to the VFD, with less than 30' of wire run. See attached photo of the exact motor we're using. My customer is arguing that they don't care if the motor burns up, they can get another one. I'd be fine with that if it wasn't hazardous area... They claim they couldn't find a inverter duty rated motor in this size (I'm looking into it).

In addition, the overtemperature protection on this motor is strange. It seems to be built into the windings and I cannot access the temperature switches to run back to a safety contact in the main control panel (to shut off power to the motor if the temperature switch opens). Apparently there are internal temperature switches in the windings of the motor that will open up and stop it. Once it cools down the switches will close. The motor even has a warning label on the side of it that it will restart automatically after over temperature. I find that strange and a little concerning. I thought code required a temperature switch that can be wired back to the control panel in hazardous areas.

And for my last (hopefully not annoying) question. Does anyone know what D.O.L. stands for? The motor cut sheet says "D.O.L. only (not suitable for V.F.D.)" Maybe do not overload? Or do not overspeed?

*Edit - I've been in touch with Weg, the motor manufacture. I've asked them the questions above as well and their tech did not have an answer. This motor is manufactured by a subsidiary (that put's Weg's name on it).

Thanks in advance!

 

[petersonra]

DOL = direct on line, i.e.- motor starter.

 

[rbalex]

DOL means "Direct On Line", which is why it isn't suitable for VFD.

Since it is a listed motor, using it with a VFD violates Section 110.3(B), hazardous location or not.

 

[rbalex]

Also, from NEMA MG-1:

12.9 Operation in Hazardous (Classified) Locations
WARNING—Motors operated from adjustable frequency or adjustable voltage power supplies or
both, should not be used in any Division 1 hazardous (classified) locations unless the motor is
identified on the nameplate as acceptable for such operation when used in Division 1 hazardous
(classified) locations.

Violating this can be a BIG FedOSHA problem.

 

[paulengr]

I think you are confused what “inverter duty” means. NEMA MG-1, Part 31 explains it in detail but boiled down there are two key differences between “standard” and “inverter” duty. The warning has nothing to do with Part 31. It applies to any motor.

The big rating in class 1 especially (you just need dust proof) is having a labyrinth. This is a special breather vent that cools any potential flames inside the motor to the point where the temperature won’t propagate a flame from inside to outside and it is strong enough to withstand the pressure while this occurs. This is for the XP example liaison proof rated motors.

The first is that the motor is modified to survive higher voltage surges. It is increased from around1000 to 1450 V. How this is accomplished is that they add phase papers between the phases at the end rings and wrap the ends of the turns with Kevlar shock cord to prevent movement before dipping and baking out the stator. In practice most motors hit 1650-1750 V after this is done.

Surge rating has to do with reflected waves. At around 50-100 feet a VFD begins to develop a reflected wave in the motor cable. The first peak is around 200-250 feet at twice the line peak voltage or about 1400 V at 460’V. It was thought that inverter duty motors fixed the problem. But it continues to increase even further at longer distances as the first reflected wave has not dissipated before a second begins and continues to reach 4 times at around 500-600 feet. The solution is to use a Dv/dt or sinus filter at the drive which removes the reflected waves.

Second difference is that it will have a rating on it for the allowable operating range over which it can self cool with maximum name plate torque. This is accomplished with extra cooling fins or oversized fans or in the case of TENV by cooling fins alone. Ultimately the best option becomes either a TEPV or TEBV. The first is pipe ventilated (supply your own blower, outside the classified area) or blower ventilated. A fan CFM varies with the square of RPM while horsepower varies directly with RPM so dropping to 50% speed decreases integral fan cooling by a factor of four. So with blower ventilated motors we can bypass this issue entirely...we get infinite speed range.

Finally this does not mean we can’t do something with a non-inverter duty motor. As shown in MG-1 charts a standard duty 1.15 service factor motor can operate down to 50% speed at full name plate torque. If the load is centrifugal (pump or fan) then the load torque also varies with the square of speed so speeds down to around 10% (6 Hz) are allowable. This is true with standard duty motors.

So NEMA MG-1 is right about making sure to take cooling into consideration. This is true of ANY VFD driven motor though, not just in hazardous locations.

 

[GoldDigger]

Paul, your analysis of potential problems is helpful, but does nothing to mitigate the standards (although not Code) requirement cited by Jraef regarding this kind of operation in a classified area.
The NEC itself probably comes into play anyway in terms of the equipment being suitable for the use, which makes NEMA MG-1 applicable.

 

[rbalex]

The OP asked if the use was an NEC violation - it is clearly a violation of Section 110.3(B) as I indicated in Post #3.

I probably should have been clearer why it is also enforceable under the FedOSHA General Duty Clause.

The NEMA MG-1 warning indicates a “recognized hazard”.

(I don’t believe an essay was necessary to answer the OP’s question)

 

[cowski]

Thanks guys. I'm going to cite these code violations to my customer and refuse to install the motor they have.

 

[paulengr]

Paul, your analysis of potential problems is helpful, but does nothing to mitigate the standards (although not Code) requirement cited by Jraef regarding this kind of operation in a classified area.
The NEC itself probably comes into play anyway in terms of the equipment being suitable for the use, which makes NEMA MG-1 applicable.

Class 2 division 1 motors must be explosion proof.. Only division 2 can be TEFC. OP stated division 1 which is highly restrictive.

My comment is entirely appropriate. See for instance NIDEC that says the same thing:

“Use of a variable frequency drive with the motors in this catalog, intended for use in hazardous locations, is only approved for Division 1, Class I, Group D hazardous location motors with a T2B temperature code, with a limitation of 2:1 constant torque or 10:1 variable torque output. No other stock hazardous location motors are inherently suitable for operation with a variable frequency drive. If other requirements are needed, including non-listed Division 2, please contact your Nidec Motor Corporation terri- tory manager to conduct an engineering inquiry.”

As I stated earlier a standard Part 30 motor can go to 2:1 constant torque as per NEMA MG-1. NIDEC is even giving a T-Code. This isn’t explaining away anything. It’s the MG-1 standard.

In division 2 areas you can use a TFC general purpose motor as per NEC which does not require a T-Code. Again the 2:1 / 10:1 torque limit exists but it also opens up the inverter duty Part 31 motors. NIDEC is avoiding this category but other manufacturers don’t and it’s not normally decided by the manufacturer since NEC specifically permits this use. Then it falls back in general purpose limitations which are the same thing: 2:1/10:1 speed range unless using inverter duty motors with expanded speed ranges.

Keep in mind the difference in design between a hazardous location and a standard duty motor. A hazardous location motor is designed with a labeynth vent that cools off gases from an internal explosion down to the name plate T-Code via the flame path approach. It is designed to withstand the maximum back pressure allowed by the vent and it is designed so that thermally it can withstand combustion of the worst case material internally fully filling up the motor or any other fault condition such as shorting to ground while maintaining surface temperatures below the T-Code. The NEMA MG-1 note just extends this to point out that you must also program the VFD with a minimum frequency using either the limit in MG-1 if one is used or the manufacturer specified lower limit, if one exists.

 

[don_resqcapt19]

Class 2 division 1 motors must be explosion proof.. ...

Actually Class II locations do not require explosion proof equipment.

502.5 Explosionproof Equipment.
Explosionproof equipment and wiring shall not be required and shall not be acceptable in Class II locations unless also identified for such locations.

 

[rbalex]

Class 2 division 1 motors must be explosion proof.. Only division 2 can be TEFC. OP stated division 1 which is highly restrictive.

My comment is entirely appropriate. See for instance NIDEC that says the same thing:

“Use of a variable frequency drive with the motors in this catalog, intended for use in hazardous locations, is only approved for Division 1, Class I, Group D hazardous location motors with a T2B temperature code, with a limitation of 2:1 constant torque or 10:1 variable torque output. No other stock hazardous location motors are inherently suitable for operation with a variable frequency drive. If other requirements are needed, including non-listed Division 2, please contact your Nidec Motor Corporation terri- tory manager to conduct an engineering inquiry.”

As I stated earlier a standard Part 30 motor can go to 2:1 constant torque as per NEMA MG-1. NIDEC is even giving a T-Code. This isn’t explaining away anything. It’s the MG-1 standard.

In division 2 areas you can use a TFC general purpose motor as per NEC which does not require a T-Code. Again the 2:1 / 10:1 torque limit exists but it also opens up the inverter duty Part 31 motors. NIDEC is avoiding this category but other manufacturers don’t and it’s not normally decided by the manufacturer since NEC specifically permits this use. Then it falls back in general purpose limitations which are the same thing: 2:1/10:1 speed range unless using inverter duty motors with expanded speed ranges.

Keep in mind the difference in design between a hazardous location and a standard duty motor. A hazardous location motor is designed with a labeynth vent that cools off gases from an internal explosion down to the name plate T-Code via the flame path approach. It is designed to withstand the maximum back pressure allowed by the vent and it is designed so that thermally it can withstand combustion of the worst case material internally fully filling up the motor or any other fault condition such as shorting to ground while maintaining surface temperatures below the T-Code. The NEMA MG-1 note just extends this to point out that you must also program the VFD with a minimum frequency using either the limit in MG-1 if one is used or the manufacturer specified lower limit, if one exists.

This is still generally irrelevant to the OP who indicated a satisfactory response had been achieved in Post #8.

Don has already indicated explosionproof equipment is neither required nor acceptable in Class II locations unless also identified for such locations. [Hint: A labyrinth isn't a key feature - See Section 502.125(A) for the actual Class II, Division 1 requirements] In addition, in Division 2, you need to read Section 502.125(B) very carefully - it isn't as easy as you seem to think. Finally, NIDEC info is only relevant IF and only IF you are installing an NIDEC motor. Otherwise, it is not a Recognized American National Safety Standard.

By the way, If you are going to discuss Classified Locations as a PE, use the correct designators for Class and Division.

Oh, what the hell, with regard to temperature markings see Sections 430.7 and 500.8(C)(4)

 

[RumRunner]

. . . .Finally, NIDEC info is only relevant IF and only IF you are installing an NIDEC motor. Otherwise, it is not a Recognized American National Safety Standard.

By the way, If you are going to discuss Classified Locations as a PE, use the correct designators for Class and Division.

You are painting with a broad brush-- the viability of NIDEC MOTOR CORPORATION motor products.

Sounds like you are outside the loop when it comes to knowledge about several products that are globally used in many industries.

Your proclamation that NIDEC is a small player in motor manufacturing --and the application for their product in hazardous location-- is unsuitable-- is suspect in your "not a recognized national standard" faulty edict.

You might want to read some financial reviews if your are not trading stock on Wall Street.

One of the largest motor manufacturers, US MOTORS is a subsidiary of NIDEC. The mother company that started in Japan. They are responsible for the manufacture of the smallest motor that computer drives Hard Disk and large motors in heavy industries.

US Motors meet all requirements by ANSI and mandates of the Department of Energy.

They also manufacture motors for precision robots in several manufacturing operations.

Perhaps it will help if you tone down your bias and keep my NIDEC stock price up.

As of Oct 16, 2020, NIDEC OTC stock price is $96.60.
A lot better than GENERAL MOTORS whose stock price at Friday's closing-- selling at measly $33.45 per share.

I have nothing against specialization-- as in your case--mastering the classification of different classes of hazardous locations.

However, when making it sound like-- the best thing that ever happened in Electrical Engineering is memorizing articles of each chapter of the NEC . ..it starts to raise some hackles.

Even going into the minutiae of admonishing a PE for not using the correct classification.

Here's some info about NIDEC CORPORATION
Technical Data & Product Design References | U.S. MOTORS

https://acim.nidec.com/motors/usmotors/service-support/technical-data

 

[rbalex]

I have nothing against NIDEC but no manufacture can speak authoritatively for the whole industry.

 

[paulengr]

Are you somehow suggesting that without any counter examples that NIDEC’s XP models are somehow novel or unique and nothing like whoever the “major” motor manufacturers are without citing a single counter example?

Citing Code does not help anyone with application. Particularly with hazardous locations where it is a performance standard, not design. I think NEC says it best when it stares that it is NOT a design document yet the response is that it is.

 

[rbalex]

Are you somehow suggesting that without any counter examples that NIDEC’s XP models are somehow novel or unique and nothing like whoever the “major” motor manufacturers are without citing a single counter example?

Citing Code does not help anyone with application. Particularly with hazardous locations where it is a performance standard, not design. I think NEC says it best when it stares that it is NOT a design document yet the response is that it is.

As pointed out earlier, no manufacturer’s explosionproof design (including NIDEC’s) has any relevance in Class II.

FWIW every manufacture thinks there's something unique about their product. I simply cited the appropriate recognized standard for ASD applications (NEMA MG-1) which for myspark's sake isn't just the NEC.

EDIT ADD: if anyone would care to read my earlier responses (carefully), I have neither implied nor inferred that NIDEC’s products were inferior.

 

[RumRunner]

FWIW every manufacture thinks there's something unique about their product. . . . .

EDIT ADD: if anyone would care to read my earlier responses (carefully), I have neither implied nor inferred that NIDEC’s products were inferior.

That's an argument that borders on non-relevance. In simple syllogistic reasoning . . .it is called "poisoning the well". An informal fallacy to discredit someone.
In the early part of your comments-- you vehemently asserted your reference regarding the non-recognized NIDEC. But now you are urging readers to revisit your comments-- claiming their understanding is not up to speed.

They are not "careful" ( your favorite term) and therefore implying that NIDEC is inferior.
To be pragmatic, I say that NEC or other building codes can not be considered SCIENCE. Most of the articles were written by people with different agenda-- most often-- to benefit towards their own ends.

When I say that the NEC is unscientific-- it means that whoever is defending the position based on what he understands can not be 100% reliable.. . that is-- when ambiguities arise.
Anyone can assert what he thinks is the right interpretation. . .and that includes yours.
Science cannot be falsified. It can be observed.

Someone might think that what he thinks is right. . .but-- there are instances where some people with extensive experience or even impeccable educational background would develop false confidence that his contentions are beyond reproach.
It is what it is because it's been done this way. So, it must be right.

That is the biggest problem in a forum like this where there is no peer-- review.. . everyone is taking his/her own shot.

When someone realizes he messed -up. . . lame excuses would emerge claiming: "I did not say that".

If an engineer designed something that failed, it is not a valid reason in terms of liability implication-- to skirt accountability. An engineer is liable for anything he did not say-- which he should have known.
ERROR and OMISSION is insurmountable in the court of law. When an engineer puts something out to the public, he is liable for every mishap, misuse or injury-- even those that were caused by outright ignorance of users.
When you say : "I did not suggest that NIDEC is inferior", it is also a fallacious argument. You implied that it doesn't meet the level of performance.

How can you be so sure that what you are thinking is-- what you think is right?

Citing an article because it is written is just another fallacy that is an appeal to pity. (Argumentum ad misericordiam.)
If I assume that you are right-- why would anyone contest its validity.

Written codes like NEC are not undecipherable. . .it's what people interpreting them that makes it so CONVOLUTED.

It is not as if --the theories of Quantum Mechanics, that are beyond our comprehension.

Pass the ketchup-- please.

...…

 

[don_resqcapt19]

...
When you say : "I did not suggest that NIDEC is inferior", it is also a fallacious argument. You implied that it doesn't meet the level of performance...…

Bob, said exactly what he meant...the information from a manufacture about their products in NO WAY applies to any other manufacturer's products. He said nothing about the " viability" of their products. It appears to me that you are the one that is reading something that is not there.

 

[RumRunner]

Bob, said exactly what he meant...the information from a manufacture about their products in NO WAY applies to any other manufacturer's products. He said nothing about the " viability" of their products. It appears to me that you are the one that is reading something that is not there.

There are none so blind as those who will not see.
It would be nice if you make your own case and not be acting like sheep being herded away.

 

[jim dungar]

There are none so blind as those who will not see.

I have read through this thread several times and cannot find where anyone passed judgement on, either explicitly or implicitly, NIDEC except for yourself. From what I see, Paulengr was discussing NIDEC products for Class I Div 1 Group D locations and Rbalex pointed out that the OP was for a Class II Div 1 application and therefore the NIDEC information was not relevant.

But regardless, personal attacks do not belong on this forum. We close threads when this happens.

 

[bwat]

There are none so blind as those who will not see.
It would be nice if you make your own case and not be acting like sheep being herded away.

So what exactly is it that you wish others to see?

This thread looks pretty clear from outside perspective. rbalex made basic statements about manufacturer's documentation only applying to products from that manufacturer. Basic stuff. You can try to say that he was saying (or implying) something else, but we can all read what he actually said...

When you say : "I did not suggest that NIDEC is inferior", it is also a fallacious argument. You implied that it doesn't meet the level of performance.

No... he clearly said that NIDEC docs only apply to NIDEC products.

Finally, NIDEC info is only relevant IF and only IF you are installing an NIDEC motor.

I truly don't see how you infer anything else out of that. It's almost like you are arguing with words that just aren't there.