Area classification

[schlag]

Area classification and T -rating. I see electrical equipement with "T" ratings. What about standard motors? Is it proper to use the insulation class plus a 20 degree hot spot to dervie a "T" rating?

 

[aolalde]

Could you explain your question with more detail?

 

[schlag]

The NEC has "T" rating for electrical equipement that is to be used in classified areas. Basiaclly the "T" rating is determined by the max skin temperature of the operating equipment. This temperature needs to be below the auto ignition temperature of normal process vapors or dust. With new motors i can purchase them with a "T" rating (usually a termal cutout), but how to handle the existing motors with no thermal cutouts?

 

[aolalde]

For American motors you should look for "explosion proof motors" constructed under supervision and bearing the "UL LISTED TAG" registration.
(UL= Underwriters Laboratories Inc.)

Motors Listed by UL must bear clearly
Class ( I, II, III)
Group ( A,B,C,D,F,G)
Division (1,2)
Operating temperature ( T1,T2,T3, etc)

The motor classification stamped on the motor plate should match the hazardous atmosphere of the intended location.

 

[sslobodan]

I don't know exactly what you are thinking by "classified areas" but if it is highly flammable station than you need to use explosion proof equipment because of construction of asynchronous motors and . If it is not explosion area you should be more specific, because explosion proof motors tend to cost 2-4x more than regular ones.... you should find the standard required for your equipment it is usually IPxx (IP54 for instance is protection usually required and IP65 can run practically under water) or NEMA standard encloses. I dont know NEMA= US standards so I cant help you much about them...

 

[dcasto]

I always use TEFC motors in Oil & Gas.

 

[djs]

Most TEFC induction motors are also rated for Class I Div 2.

 

[motorspert]

All hazardous areas have a T rating which is the maximum surface temperature allowable for any equipment installed in the area. The temperature is determined depending on which gases are likely to be present and the corresponding ignition temperature of those gases. The most common is T3 which relates to 200C. So, the motor needs to have all parts lower in contact with the gas lower than 200C. The windings are normally not of too much concern - the two areas that need most attention are the anti-condensation heaters, they have to be derated, which means they are bigger and more costly. The other aspect is the rotor bars which can get hot during starting, this is a particular issue for Exe motors and they are issued with a safe stall time, if i remember correctly class 1 div 1 has similar requirements(my memory is a bit cloudy here).

Flameproof motors have different rules of engagement. They have to contain the energy of any potential explosion and any gases that escape have to be cooled down to prevent ignition. Thus flp motors tend to be big thick and heavy.

djs statement about most TEFC motors being suitable for cl1 div 2 is a generalisation and if anti-condensation heaters are fitted then they should be changed, and this is usually a simple mod.

 

[cherry2000]

T rating of a Motor ( or for that matter any electical equipment ) is a prerogative of the manufacturer. It is an inherent part of the design of the equipment and there are lots of ways to mitigate T ratings. Hence no effort should be made in deriving T ratings. Instead certified equipment with a nameplete as described by aloalde should be obtained. Using uncertified equipment in classified area is a dangerous & unlawful practice. Equipment Data sheets need to clearly specify the Zone/Div and also the Gas Group & Temp Class that is expected.During vendor dwg review, the details need to be carefully cross checked.

 

[rbalex]

Three-phase motors are rarely "rated" for Class I, Division 2, whether they are TEFC, TENV, Open-Drip Proof, etc. They aren't required to be. See the last sentence in Section 501.125(B) in the 2005 NEC. Using space heaters are a different consideration. Read the entire Section.

Since these are considered to be “General Purpose Equipment” they require no special marking either – See Section 500.8(B)(6)(a).

To answer the OP though, considering the operating temperatures should nevertheless be a consideration. See Section 501.125(B) FPN No. 1. While FPNs are not technically part of the NEC, failing to observe them is foolish. NEMA MG-1 will detail the various “rises” given motor designs with specific insulation systems will have on internal and external surfaces.