Induction Motors Classified area

[e&ilayman]

Need help with class 2 div II group G area motor installation. Dust in area has ignition temp 275 degree C can we use TEFC induction motors with Class B insulation? Also does lighting and solenoid valves in the area need to be T2B rated? Thanks in Advance
Thanks for help rbelax

 

[rbalex]

Re: Induction Motors Classified area

Assuming a maximum operating ambient of 40C, a TEFC (Totally Enclosed Fan Cooled) motor, with a Class B rise would be acceptable in the Class II, Division 2, Group G application you have described. See 502.8(B) & 500.8(C)(2). Note: Table 500.8(C)(2) is not applicable.

Solenoids marked T2B would be acceptable, but there are additional requirements. See 502.7(B)(2).

Luminaires (Lighting Fixtures) are also a special case in Class II. See 502.11(B) Note: the 80 percent rule, common to Class I locations does not apply.

 

[e&ilayman]

Re: Induction Motors Classified area

Thanks for the reply but can't help ask the logic in motor insulation class as compared to nema T code for explosion proof motors. Why would insulation class be considered, it has no relevance to how hot the motor can get under extreme conditions. My thoughts are that under normal circumstances the motor will trip or fail before becoming an ignition source and thats the logic in making the distinction between solenoid lighting etc. I can except logic its hard to except interpretable rules.

 

[rbalex]

Re: Induction Motors Classified area

You?ve changed the question. You asked "...can we use TEFC induction motors with Class B insulation", not the rationale behind it.

Go back to 430.7(A)(5). It?s one of the required [NEMA] markings on motors. It may either be the, ?Rated temperature rise or the insulation system class and rated ambient temperature.? Also note I originally used the term Class B rise rather than Class B insulation; they aren?t necessarily the same thing although a Class B insulation implies no greater than a Class B rise.

Per NEMA MG-1, a Class B rise implies not more than an 80 to 90C temperature rise over a 40C ambient depending on temperature measurement means and application and construction of the motor. In any case, the maximum temperature is 130C, well within the limits of the AIT you specified.

Because this is Division 2, the emphasis is on ?normal operation? use of the motor. See the end of the sentence in 502.8(B). Also see 500.8(A)(5).

If you are saying you prefer to use a motor identified for Class II, Division 1 go ahead.

 

[e&ilayman]

Re: Induction Motors Classified area

Thanks again but when I read the two paragraphs (listed below)from Reliance manual I understand clearly the need for T codes for motors and your original statement of if the motor skin temperature does not rise more than the insulation classB rating then the TEFC motor will work!
Insulation: Since there are various ambient temperature conditions a motor might encounter and different temperature ranges within which motors run and insulation is sensitive to temperature; motor insulation is classified by the temperature ranges at which it can operate for a sustained period of time.
T code: A National Electrical Code index for describing maximum allowable "skin" (surface) temperature of a motor under any normal or abnormal operating conditions. The "T" codes are applicable to U.L. listed explosion-proof motors. The skin temperature shall not exceed the minimum ignition temperature of the substances to be found in the hazardous location. The "T" code designations apply to motors and other types of electrical equipment subject to hazardous location classification.
P.S. I believe there should be an open flame every 50 feet in an refinery/chemical plant it would ignite small fires that burn up equipment not spread and explode killing many people. Maybe the code is to protect property and not lives!

 

[rbalex]

Re: Induction Motors Classified area

The Reliance material doesn?t tell the entire story. Per Section 500.8 (B):

(B) Marking. Equipment shall be marked to show the class, group, and operating temperature or temperature class referenced to a 40?C ambient.

In other words, ?T? ratings are also based on a 40C ambient.

A Class B temperature rise (90C over a 40C ambient) is slightly better than ?T4? (135C).