Motor Thermal Switch Requirement in Class 1

[nmelectrical]

In a class 1 div 2 area we have an installed XP motor, does the code require the thermal switch be connected?
My understanding of 501.125, is that the thermals are required to prevent the enclosure temp from exceeding the T rating (which must be less than 80% of the AIT) of the motor and that is only required in a C1 D1 area when using a motor specified in A(2) or A(3).

 

[rbalex]

You need to review 501.125(B) again for the T rating requirement; it only applies to motor space heaters. If it is a NEMA motor, the thermal switch is for overload protection only; whether it must be in the control circuit or not is up to the manufacturer. Check their installation instructions. Some IEC design motors may require them, but for NEMA motors it has nothing to do with Classified locations. See 500.8(B)(5) The significance of this reference is that overload is not a consideration for ?normal? motor operation in Division 2 (oddly enough neither is starting a motor in either Division)

 

[nmelectrical]

Reading through 500.8 again I have to make the assumption that one would be required to use the thermal switch due to 500.8(B)(1):
In addition, Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor.

I guess I am making the assumption here that the thermal switch in a NEMA motor would open before the temp reached the stamped "T" rating on the motor...which would be the best way to comply with 500.8(B)(1).

Or am I way off base here.

 

[rbalex]

The following is excerpted from NEMA MG-1

Section I GENERAL STANDARDS APPLYING TO ALL MACHINES
Part 1?REFERENCED STANDARDS AND DEFINITIONS
DEFINITIONS
?
MISCELLANEOUS
?
1.72 THERMAL PROTECTOR
A thermal protector is a protective device for assembly as an integral part of the machine and which, when properly applied, protects the machine against dangerous over-heating due to overload and, in a motor, failure to start.[RBA Note: underline added]
NOTE? The thermal protector may consist of one or more temperature sensing elements integral with the machine and
a control device external to the machine.
1.73 THERMALLY PROTECTED
The words ?thermally protected? appearing on the nameplate of a motor indicate that the motor is provided with a thermal protector
?

Throughout the rest of MG-1 there are various statements about motors used in classified locations with statements similar to the following:
[RBA Note: there are variations to the following text, but it is always with reference to non-sinusoidal power supplies]

?
30.2.2.10 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.

For motors to be used in any Division 2 hazardous (classified) locations, the motor manufacturer should be consulted.

Failure to comply with this warning could result in an unsafe installation that could cause damage to property or serious injury or death to personnel, or both.

In general, motors are neither listed nor labeled as defined in Article 100. Explosionproof motors are listed but it actually applies only to the enclosure. Motors are rarely listed for Division 2 applications.

Even for explosionproof motors, integral thermal protectors are strictly for overload and/or locked rotor conditions ? neither of which are relevant to Division 2 installations. The ?T-rating? is determined by the motor design and insulation class ? not a thermal protector.

 

[nmelectrical]

Thanks for your help/clarifications.

I still am having an issue (in my mind at least) with 500.8(B)(1), how do installations comply with this rule?

 

[rbalex]

Thanks for your help/clarifications.

I still am having an issue (in my mind at least) with 500.8(B)(1), how do installations comply with this rule?

Lately, I have been reminding folks that identified is a defined term in Article 100 and it is not necessarily required to be listed or labeled – no matter what the definitions FPN implies.

500.8(B) Approval for Class and Properties.
(1) Equipment shall be identified not only for the class of location but also for the explosive, combustible, or ignitable properties of the specific gas, vapor, dust, or fibers/flyings that will be present. [RBA Note: underline added]

Compare this with 500.8(B)(3) which recognizes that certain types of general purpose equipment is permitted in Division 2.

 

[nmelectrical]

I am in agreement with you about the first sentence, however the rest of that article states:
In addition, Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor. Class II equipment shall not have an external temperature higher than that specified in 500.8(D)(2).

The bold portion is what I am having a tough time with.

 

[rbalex]

This discussion started with Class I applications in the OP, not Class II, and there are some conceptual differences. For example, see Section 502.5 where it states explosionproof equipment is neither required nor acceptable in Class II unless identified for Class II.

However, with respect to motor thermal protectors, the rules are still the same; i.e., motor thermal protectors are for overload/locked rotor applications only. They have no direct bearing for determining "suitability" in Classified locations - Class I, II or III.

The rules for motors in Class II are in Section 502.125. Note they don?t make any issue of thermal protectors at all. Again, especially in Class II, Division 2 (also the original OP context) ?general purpose? motors are acceptable with certain constraints, none of which involve thermal protectors.

Compare 502.125 with its reference to 500.8(D)(2). Also compare both with Section 430.7, especially Subsections 430.7(5), (9) and (13). A NEMA motor?s temperature rating is based solely on the ?design type? (A, B, C or D) and the insulation class. The only temperature marking for motors the NEC requires cannot be based on a thermal protector, since they are only provided for overload/locked rotor; i.e., it protects the motor not the Classified location.

 

[nmelectrical]

Sorry i placed the bold tags around the wrong section of text, I am still referring to to C1D2 areas. And in particular this sentence from 500.8(B)(1)
Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor.

I just am not sure how this requirement is met.

I am suggesting that the only way to I can see to comply with the above NEC requirement is to have the motor with a T Code rating below the ignition temp of the gas/vapor it may come in contact with. I also suggest that the only way the motor can be below this Temp rating is to have something that ensures the temp is not above said temperature.

 

[rbalex]

Sorry i placed the bold tags around the wrong section of text, I am still referring to to C1D2 areas. And in particular this sentence from 500.8(B)(1)
Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor.

No problem - but then my previous answers still stand unless you are simply being argumentative.

...I am suggesting that the only way to I can see to comply with the above NEC requirement is to have the motor with a T Code rating below the ignition temp of the gas/vapor it may come in contact with. I also suggest that the only way the motor can be below this Temp rating is to have something that ensures the temp is not above said temperature.

In that case, I've told you where and how to derive the appropriate "T-Code" from the motor's nameplate [Section 430.7(A)(5)]. Since Division 2 only requires "normal" ignition sources to be recognized [500.5(B)(2)] and overloaded, locked rotor (or even simply starting) is not considered "normal" for motors [500.8(B)(5)] you have no need to worry. Of course, it is still perfectly ok to use a thermal protector, but let me assure you it won't "...ensure the temp is not above said temperature" - it just isn't designed for that purpose.

The NEC is not "... a design specification or an instruction manual for untrained persons."[90.1(C)] That is, you may not find all relevant "Code" information you want in a single location. As a former member of both CMP 11 (1996) and CMP 14 (2002), I'm fairly confident that I'm not an "untrained person" with respect to this particular issue.

 

[weressl]

Sorry i placed the bold tags around the wrong section of text, I am still referring to to C1D2 areas. And in particular this sentence from 500.8(B)(1)
Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor.

I just am not sure how this requirement is met.

I am suggesting that the only way to I can see to comply with the above NEC requirement is to have the motor with a T Code rating below the ignition temp of the gas/vapor it may come in contact with. I also suggest that the only way the motor can be below this Temp rating is to have something that ensures the temp is not above said temperature.

Not so and not exactly. Class I, Division 2 equipment should not be a source of ignition under normal operating conditions. Since the motors are designed with a recognized class of insulating materials that have a temperature rise limit above ambient, depends on the Class of the insulating material. Motors are normally designed to operate well below this temperature, but it varies from manufacturer-to-manufacturer. If the motors is installed according to the NEC and is equipped with overload and short circuit, stall protection, we can be assured that the motor will always operate at normal operating conditions. It is highly unlikely that you will find a chemical whose AIT will be below the temperature rise assigned to the Classes of insulation plus 25C* ambient. The Classes are as follows: A 85C*; B 110C*; F 135C* and H 155C*. These temperatures are of course would not occur on the exposed surface, as the 'hot spot' is normally buried somewhere within the slot.

 

[nmelectrical]

Thanks for helping me out, in no way did i want to come across as argumentative. I am only trying to better understand this issue and you have helped me do that.