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  1. #1
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    Motors in Hazardous Locations

    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?
    Time is of the essence, and I am low on essence. ~ Graham Hill

  2. #2
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    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.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
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    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?
    Time is of the essence, and I am low on essence. ~ Graham Hill

  4. #4
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    Quote Originally Posted by fifty60 View Post
    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.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  5. #5
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    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"
    Time is of the essence, and I am low on essence. ~ Graham Hill

  6. #6
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    Quote Originally Posted by fifty60 View Post
    ...
    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.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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