Motors in Hazardous Locations

[fifty60]

I know precautions have to made for motors in Class 1 div II locations, for example, for the overload contacts and other switching mechanisms employed by the motor have to be identified for Class 1 Div I....

I do not know about Servo motors in hazardous locations...What precautions need to be made for servo motors? Is the PWM used to control the servo motor inherently a problem for hazardous (Class 1 div II) locations? Is there any other ignition source on a Servo?

 

[rbalex]

I usually don't make a big deal about it but, if you're going to be an engineer, "Class" uses Roman numerals and "Division" uses Arabic numerals; so it's Class I, Division 2 we're talking about.

The rules changed a bit in 2017 and, even if the Code you are under is an earlier edition, manufacturers will usually construct to the latest edition. See Section 501.125(B).

Basically, motors in Division 2 must now be identified. This does not necessarily mean listed or labeled specifically for Division 2 but it does mean there are a few more hoops to jump through to recognize that they are suitable. [See Section 500.8(A); especially 500.8(A)(3)]

Without a great deal of evaluation a servo-motor is not automatically identified as suitable. Unless its inherent harmonics would cause undue heating, PWM has no bearing on the evaluation.

 

[fifty60]

So for a Class I div 2 environment, an evaluation can be done on the motor, and "non-incendive circuit" can be used as the inherent protection method of the motor. The "non-incendive circuit" protection method could be used in the identification process of a motor that can be used in Class I div 2? If the motor is identified as a non-incendive circuit per the means of 500.8(A), the motor would be acceptable to use in a Class I Div 2 area?

 

[rbalex]

So for a Class I div 2 environment, an evaluation can be done on the motor, and "non-incendive circuit" can be used as the inherent protection method of the motor. The "non-incendive circuit" protection method could be used in the identification process of a motor that can be used in Class I div 2? If the motor is identified as a non-incendive circuit per the means of 500.8(A), the motor would be acceptable to use in a Class I Div 2 area?

It's kind of "iffy" (hoops) there but, assuming all components are suitable for nonincendive applications, it sounds acceptable to me.

BTW, when used with respect to classified locations, "Class" and "Division" are capitalized. They may be abbreviated though.

 

[fifty60]

I am not trying to do anything iffy, or jump through hoops. At least I am hoping to not do anything iffy. What should I be looking for when I evaluate the servo motor? I know some servo's have potentiometers in them...would that disqualify it as being non-incendive? What else in a servo would make it a non-incendive circuit?

I am interested in sending a servo motor off to another inspector to have it "identified" for Class I Div 2...but would like to be certain of it passing before I send it away to the inspection..

I am also unsure about "suitable for nonincendive applications". Does a non-incendive circuit have to be "suitable for nonincendive applications"

 

[rbalex]

...
I am also unsure about "suitable for nonincendive applications". Does a non-incendive circuit have to be "suitable for nonincendive applications"

You are now facing the smallest hoop out there complete with flames and lined with razors. Simply put, does your design and all of its pieces and parts comply fully with ANSI/ISA-12.12.01-2013? That document is the standard for nonincendive systems.

 

[fifty60]

Thank you, I will look into this document. So basically any equipment that wants to use "non incendive circuit" as a protection method needs to meet ANSI/ISA-12.12.01-2013...or at least if it meets this you have a good argument to state that the equipment is a non incendive circuit and can be used as a protection method for Class I Div 2?

 

[rbalex]

It is now ANSI/ISA-12.12.01-2015, Nonincendive Electrical Equipment for Use in Class I and II, Division 2 and Class III, Divisions 1 and 2 Hazardous (Classified) Locations. It is referenced throughout the various nonincendive definitions in Article 100. (Except is has recently been updated to 2015) What was your intended basis for evaluating your design otherwise?​

 

[fifty60]

To use the non-incendive circuit protection method, I would have just used the definition of non-incendive circuit in Article 500...

 

[rbalex]

To use the non-incendive circuit protection method, I would have just used the definition of non-incendive circuit in Article 500...

If you are using the 2014 or earlier edition it also refers to ANSI/ISA-12.12.01, just the edition's year is different. Essentially you are not qualified to make the determination on your own. It is much like determining the electrical area classification - it can't be done from the NEC itself (except Articles 511 to 516). Compliance with the NEC is determined by external documents and standards. Just as you can't tell if a product is NRTL certified without the NRTL's marking. Unless you demonstrate compliance with the relevant ANSI/ISA-12.12.01 (determined by the relevant NEC edition) an AHJ has no basis for determining if a circuit is nonincendive. Usually, the latest edition of ANSI/ISA-12.12.01 what a NRTL will certify to.

Incidentally, there is no hyphen in nonincendive.

 

[fifty60]

This is something that has confused me. Who is ultimately responsible for making the determination on the suitability of equipment for a hazardous location? Is it the AHJ, which I know varies from town to town...and in some instances is an NRTL? Is the best approach to use the NEC and relevant ANSI standards and have them as a defense/explanation of your design choices to present to the final AHJ?

 

[petersonra]

This is something that has confused me. Who is ultimately responsible for making the determination on the suitability of equipment for a hazardous location? Is it the AHJ, which I know varies from town to town...and in some instances is an NRTL? Is the best approach to use the NEC and relevant ANSI standards and have them as a defense/explanation of your design choices to present to the final AHJ?

In general:

The AHJ is responsible for determining the acceptability of anything you use. However, keep in mind the AHJ is not the same thing as the inspector.

Most AHJ will accept an NRTL listing as meaning the equipment is acceptable for a particular use. Some AHJs have rules requiring that a listed product be considered acceptable for a use within the listing.

Identified (as applied to equipment). Recognizable as
suitable for the specific purpose, function, use, environment,
application, and so forth, where described in a particular
Code requirement.

Is a different concept than listed as it does not have to involve an NRTL, although it could and often does. If an NRTL is not involved, most times it is the manufacturer of the product that would so identify something as being suitable. An AHJ is not required to accept the manufacturer's judgement of suitability but most do.

I am not entirely sure what you are proposing to do. If you want to evaluate a motor made by someone else on your own, I think you are going to have a tough time getting an AHJ to accept that evaluation. If you want to use the motor manufacturer's evaluation, chances are pretty good most AHj would accept it without much in the way of comment.

 

[rbalex]

This is something that has confused me. Who is ultimately responsible for making the determination on the suitability of equipment for a hazardous location? Is it the AHJ, which I know varies from town to town...and in some instances is an NRTL? Is the best approach to use the NEC and relevant ANSI standards and have them as a defense/explanation of your design choices to present to the final AHJ?

First, thanks Bob (petersonra) – good response.

Second, fifty60, as an exercise left to the student, (you will remember it better) I’m going to suggest you start with NEC Section 110.2 and follow the chain of definitions (Article 100) and Informational Notes (IN) that arise. Ultimately, the chain will lead to the definition of Authority Having Jurisdiction and its rather long and moderately convoluted Informational Note.

110.2 Approval. The conductors and equipment required or
permitted by this Code shall be acceptable only if approved.

Informational Note: See 90.7, Examination of Equipment
for Safety, and 110.3, Examination, Identification, Installation,
and Use of Equipment. See definitions of Approved,
Identified, Labeled, and Listed.

[RBA Note: Identified’'s IN may be misleading – read it carefully]

For an even better exercise, see FedOSHA’s definitions of Accepted, Acceptable, and Approved with respect to electrical installations. Eventually it will lead to who the AHJ actually is with respect to FedOSHA.

The NEC definitions/INs will lead you to the fact that there may be many AHJs in any particular case – and they all have to be satisfied. FedOSHA’s definitions are often copied in some form by most StateOSHAs.

I’ve been teaching young engineers (even a few PEs) nearly 50 years that you must first be an accountant and then a lawyer before you can actually do any engineering.