TEFC Motors in Class 1 Division 2 locations

[haze10]

TEFC motors in a Class 1 Division 2 locations is permitted per NEC providing no arcing contacts NEC 501.125B4.
But TEFC motors don't normally come with T codes on the label. If a Div2 area is say T3, can you use a generic TEFC motor without thermostats (without surface heaters or arcing contacts). The NEC seems to be saying this is ok.

 

[Gr8blu]

haze10: Please read the whole section of the code. First, it's for CLASS II, DIVISION 1 environments (i.e., dust), not Class I Division 2. Second, it ALSO requires that the machine meet the temperature restrictions of 500.8(C)(2), which indicates two things: 1) The machine nameplate MUST show a T-code. 2) If teh dust can dehydrate or carbonize, the maximum surface temperature under normal operation cannot exceed the LOWER of the dust's auto-ignition temperature or 165 C ... which means the T-code on the machine has to be T3B (165 C), T3C (160 C), T4 (135 C), T4A (120 C), T5 (100 C), or T6 (85 C).

Equipment that was manufactured, installed, and operated prior to 2004 is assumed to meet the following maximum surface temperature conditions: Group E (200 C), Group F (150 C), and Group G (120 C). Replacing these with modern equipment reverts back to the current standard requirements.

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[haze10]

I'm in the 2020 NEC and 501.125(B) is for Class I, Division 2. Sub (3) is the reference to 'open' or 'non explosionproof' motors. There is no mention about surface temp, only non arcing components. Sub (4) refers to surface temp, but only when space heaters are installed. In the blue interpretation text, there is also the mention of heaters, but again referring to space heaters. Your reference for Class II is not in question. What I am thinking is that since Div 2 only has a flammable concentration under 'abnormal' conditions, the chance of a motor overheating at the exact moment an abnormal condition occurs is regarding as remote, hence the disabling of the motor run with thermostats is not required.
I know manufactures are now making C1D2 motor labels, but is the NEC specifically states that open and non-explosion proof motors are ok. As I said, typical TEFC motors don't come with T code ratings. So is it ok to use TEFC in C1D2 without thermostats?

 

[haze10]

Found this in an ECM reference:
Though TEFC motors typically don’t have a T-Code stamped on the nameplate with the maximum surface temperature, internal and external temperatures of the motor must be considered. IEEE Std. 841, IEEE Standard for Petroleum and Chemical Industry — Premium-Efficiency, Severe-Duty, Totally Enclosed Fan-Cooled (TEFC) Squirrel Cage Induction Motors — Up to and Including 370kW (500 HP), Section 5.4.2, states: “Temperature Rise ― When operated at rated voltage, frequency, and power, the average temperature rise of any phase of the stator winding shall not exceed 80°C as determined by the winding resistance method. Maximum exposed internal and external surface temperatures shall not exceed 200°C under typical service conditions at 1.0 service factor (SF).” Looking at NEC Table 500.8(C), a maximum 200°C temperature is equivalent to a T3 rating. It isn’t unusual though, in a petrochemical plant, to have areas where the T-code is T3A-T3C. In these cases, normal TEFC motors may run too hot and cannot be used.

The surface temperature of any motor space heaters installed for the prevention of condensation must also be considered in hazardous locations [See Sec. 501.125(B)(4)].

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This would imply that typical TEFC motors would be ok in T3 and above areas.

 

[Gr8blu]

haze10: My apologies - I was looking at an earlier Code iteration (2011, I think). The changes between that and 2020 are many!

What the 2020 edition does indicate is that a machine installed in a Class I environment must either have the correct nameplate markings (and proof that it meets maximum allowable surface temperature for the specific hazard) per 500.8(B)(1) ... or be "general industrial" construction per 500.8(B)(3) - which indicates it is not allowed to constitute a potential source of ignition under normal operating conditions.

Since a Division 2 classification means the hazard is not present under normal conditions, a "general industrial" design won't ignite anything. On the other hand - if somehow the incendive material DOES enter the area of the machine, do you really want to bet the farm on it not igniting? The cautious approach would be to ensure an appropriate enclosure and/or appropriate T-code rating.

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