Explosion Proof motors an connecting thermostats

[haze10]

Showing my age, but, years ago motor manufacturers would make Class 1 EX motors, and Class 1 and 2 EX motors. Motors that were exclusively Class 1 often didn't have internal thermostats and would have a T code of T2B (or T2C). Today, most manufacturers are limiting inventory and only selling dual rated Class 1 and 2 EX motors, often at a Temp code of T3C, but with internal thermostats. A few motors are listing multiple T codes depending on ambient temperature and whether or not the thermostats are connected. This is from a Hyundai website on their EX motors.
Unique multiple rating system for 40° and 55°C ambient
143T-215T: T2C at 40°C, T2B at 55°C, T4 when thermostat is connected
254T-286T: T2D at 40°C, T2C at 55°C, T4 when thermostat is connected
324T-444T: T3 at 40°C, T2D at 55°C, T4 when thermostat is connected

With the dual rated motors you are only getting one Temp code on the nameplate, usually T3C is common. If the motor is going in a Class 1 area, and replacing a Class 1 only rated motor, there is the likely possibility that the original motor had no thermostats (or "P" leads) connected back to the motor starter, or even the local stop button. Since there is only one T code on the label, and since you don't know what the T code would be without the thermostats, and you are obligated to not exceed the T code assigned to the area - then in order to maintain the nameplate T code you have to wire in the thermostat leads. Hopefully there is a stop button nearby.

So, my inquiry is this:
Are you finding it harder to find Class 1 only motors without thermostats?
On the dual rated Class 1 and 2 motors, is the manufacturing giving you an alternate T code without thermostats.
If you have a motor with only one T code and it came with thermostats, assume they have to be connected to keep the nameplate rating?

For C1 Div 2 areas, I came across this from ECM magazine:
"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).”"

Couple problems I see here are: most motors are coming through with 1.15 service factors. I assume that if you pick the Overload based on 1.0 SF then you can use the IEEE value of 200C. That gets you a T3 temp code. If you need something more strict, you can order the motor with internal thermostats.

Looking for some comments from those that know motors. Any and all comments appreciated.

 

[Gr8blu]

haze10 Hazardous locations are broken down by CLASS, DIVISION OR ZONE, GROUP, and TEMP CODE.
In North America, the method is called the CLASS system (CLASS / DIVISION (ZONE in Canada)/ GROUP / TEMP CODE).
CLASS refers to the material causing the hazard: Class I = gases / vapors / flammable liquids, Class II = (combustible) dust, Class III = (ignitable) fibers / flyings.
DIVISION (or ZONE) refers to the conditions when the hazard exists: DIV 1 = ZONE 0 or 1 = normal operation, DIV 2 = Zone 2 = abnormal operation.
GROUP refers to the hazard itself (Groups A-D include the gases, Groups E-G include the dusts, and no group for fibers)

In Europe and the rest of the world, the method is called the ZONE system (ZONE / GROUP / TEMP CODE).
ZONE refers to the nature and probability of the hazard: ZONE 0 = always present, ZONE 1 = part of normal operation, ZONE 2 = only in abnormal conditions.
GROUP refers to the type / material of the hazard: GROUP I = Mines (firedamp or other naturally-occurring flammable gas mixtures), GROUP II = Explosive gases, GROUP III - combustible dust and fibers.

There are several ways that a machine can be designed/constructed to combat a "hazard". The first of these is "explosion containment" - where the explosion is allowed to occur, but only in a contained area. The structure will not fail from the explosion (and hence will not allow the explosion to propagate to the surrounding medium). A second method is, "segregation" - where the electrical component are separated/isolated from the explosive mixture. This can include such practices as pressurization, encapsulation, oil immersion, and/or powder filling. Last method is "prevention" - which is where all the additional letters come from that follow the EX designation on a nameplate.

EX ia (Intrinsic, single fault): limits the energy storage to a very low level (typical for instrumentation, where V < 30 volt, I < 100 milliamp). Tested under fault and normal conditions
EX ib (Intrinsic, multiple fault): limits the energy storage to a very low level (typical for instrumentation, where V < 30 volt, I < 100 milliamp). Tested under fault and normal conditions
EX e (Increased Safety): prevents excessive surface temperatures and arc/spark production - both INTERNALLY and EXTERNALLY - under normal operation
EX nC (Non-Incendive): Similar to Intrinsic but only tested under normal conditions (can also include hermitically sealed and/or energy limited)
EX m (Encapsulation): potting compounds, for example
EX d (Flameproof): will not allow internal flame to propagate to external medium
EX o (Oil immersion): electrical equipment submerged in oil bath
EX q (Powder filled): electrical equipment surrounded by non-combustible powder and contained in another enclosure
EX p (Purge and/or Pressurized): use of inert gas to force combustible material out (purge) or keep internal volume at high enough pressure to prevent ingress of external medium (pressurize)
EX nA (Non Sparking): nothing can create an arc or spark

For the record, there are very few machines that are truly "explosion proof". Typically, these would be rated under 370 kW and above 1000 rpm, and probably below 500 V. This is because the internal volume can contain a large amount of explosive material - yielding very high pressures on joints and seals, which in turn have to be reinforced. Once the dimensions of a plate surface (like the end of a machine) go above a certain area, it becomes impossible to apply enough force to the circumference and use a thick enough plate to withstand the overpressure condition. As you might guess, proof-of-concept testing for these machines is very destructive (and expensive).

Current trend and recommendation for IEC and NEMA is to nameplate equipment properly (e.g., SF = 1.0 ONLY). From previous usage, it's best to read the fine print associated with non-unity service factors. Typically, the temperature rise shown on the nameplate was for SF = 1.0 operation, with "non-injurious" heating at elevated SF to be understood. This did not mean the above-1.0 SF operation met the requirements of a restrictive T-code for the classified environment - rather, it meant the machine would not see temperatures so high that electrical insulation integrity would be compromised.

Lastly: the use of the temperature "switch" on modern equipment is not necessarily for the major components, but is actually used to cycle the anti-condensation heater on and off to prevent excessive surface temperatures. Operating without the switch means that the heater could get hot enough to ignite any of the process gas which somehow managed to enter the machine enclosure. Alternative methods are available to meet the requirements of a hazardous location - they just aren't as simple or as low-cost to implement from a manufacturer perspective.

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