Class 1 Div 2 Motor Thermal Switch Contacts

[jtrry]

NEC classified area question.

Waste water lift station (Class 1, Div 2) - pump is 460v 3 ph and explosion proof rated. Pump motor has thermal over load switch in windings that close when (if) the motor overheats.
Question is do these switch leads that come out in the motor cable need to be isolated by an intrensically safe barrier or can they go directly to the motor control ckt. without isolation - ?

I'm thinking they may be exempt from the IS barrier rqmt due to the fact they are in an explosion proof motor - unlike the float switches which are not.

This was posted to the NEC section yesterday - it should have been in the hazadous section - hope you can help

 

[rbalex]

Waste water lift station (Class 1, Div 2) - pump is 460v 3 ph and explosion proof rated. Pump motor has thermal over load switch in windings that close when (if) the motor overheats.
Question is do these switch leads that come out in the motor cable need to be isolated by an intrensically safe barrier or can they go directly to the motor control ckt. without isolation - ?

I'm thinking they may be exempt from the IS barrier rqmt due to the fact they are in an explosion proof motor - unlike the float switches which are not.

This was posted to the NEC section yesterday - it should have been in the hazadous section - hope you can help

Is the motor control circuit truly rated intrinsically safe (IS)? If so, has it been installed per the manufacturer?s control drawing as required by Section 504.10(A)?

It is not likely the circuit is IS since you mentioned the power conductors and control conductors are in a common cable. You still need a control drawing for that portion of the system that may be IS. I also get the impression you believe an IS barrier does something it doesn't do.

 

[petersonra]

would you even need an XP motor in a div2 area?

 

[rbalex]

would you even need an XP motor in a div2 area?

Oddly enough, if the thermal cutout is inside the motor - yes.

 

[jtrry]

Is the motor control circuit truly rated intrinsically safe (IS)? If so, has it been installed per the manufacturer?s control drawing as required by Section 504.10(A)?

In my limited understanding of this subject, it seems wiring in the classified area must comply with appropriate wirtin methods of Sec 500 (ie explosion proof) OR be at such a minimal power as not to be able to create an ignition source. A way of acomplishing the latter is to use an I.S. barrier to limit the power of the ckt in the hazardous location.

"Is the motor control circuit truly rated intrinsically safe (IS)?"

The motor control ckt is a contactor with 120 VAC coil. I doubt this would constitute an intrensically safe ckt.

"If so, has it been installed per the manufacturer?s control drawing as required by Section 504.10(A)?[/COLOR]"

There is no mfgr's control drawing - I have designed the control ckt.

"It is not likely the circuit is IS since you mentioned the power conductors and control conductors are in a common cable. You still need a control drawing for that portion of the system that may be IS. I also get the impression you believe an IS barrier does something it doesn't do.

"

I agree, it's not IS.

The question relates to wheather or not an IS barrier is required in light of the fact the contacts reside inside of the XP motor?

Thanks for any help you may be able to provide.

 

[rbalex]

I agree, it's not IS.

The question relates to wheather or not an IS barrier is required in light of the fact the contacts reside inside of the XP motor?

Thanks for any help you may be able to provide.

Since the control circuit is not IS, an IS barrier would make no difference whether the motor is XP or not. The bottom line is that, in the installation as you have described it so far, an IS barrier is unnecessary because the motor is XP.

A cautionary note: if the motor were not XP, an IS barrier alone would probably not be adequate either.

 

[weressl]

NEC classified area question.

Waste water lift station (Class 1, Div 2) - pump is 460v 3 ph and explosion proof rated. Pump motor has thermal over load switch in windings that close when (if) the motor overheats.
Question is do these switch leads that come out in the motor cable need to be isolated by an intrensically safe barrier or can they go directly to the motor control ckt. without isolation - ?

I'm thinking they may be exempt from the IS barrier rqmt due to the fact they are in an explosion proof motor - unlike the float switches which are not.

This was posted to the NEC section yesterday - it should have been in the hazadous section - hope you can help

• The motor does not need to be explosionproof.
• You would think that now, since it is XP rated, it needs to be installed as XP. Not so.
• The thermostat switch inside of the motor only needs to be wired to maintain the Class I, Division1 rating. Since you are in Division 2 area, you do not need to wire it up to the control circuit. Hence the motor can be considered as an ordinary TEFC assynchronous motor and your power wiring can be installed in any manner acceptable to the NEC for Div.2 and if you use tray cable in open raceway, you won't evcen need a sealoff on the peckerhead.
• Should your installation be in Division 1, your motor power wiring needs to be sealed. Should you 'decide' to wire the thermostat as an IS circuit, you would need a separate sealed-off opening on the peckerhead to wire that circuit separate from the power circuit.
• IMO you can't wire the thermostat as an IS circuit unless it is wired into a separate JB from the main power connections.

 

[rbalex]

Laszlo?s analysis is very good. The third bullet needs expansion though. The switch is not required to maintain the XP rating; rather it is required to maintain the motor?s temperature rating.

US domestic motors are something of an unusual case with regard to listing and labeling. Except for motors in Classified locations, NEMA MG-1 is the sole authoritative ANSI Standard for motor construction in general applications.

The NEC does not require motors to be listed or labeled in general. As a result, no NEMA motors are listed for ?ordinary locations? in US domestic applications even though UL has a category code (PRGY) to list them.

Oddly enough, the NEC doesn?t actually require motors to be listed or labeled for classified locations either. Motors for Division 1 are simply required to be ?identified.? Listing/labeling is the most common method to identify a motor in Class I, Division 1 applications. The UL category code for Division 1 motors is PTDR. The basic evaluation standard is ANSI/UL 674, "Electric Motors and Generators for Use in Division 1 Hazardous (Classified) Locations."

Since certain motors for ?ordinary locations? are acceptable in Division 2, they were not generally listed specifically for Division 2 applications until recently. Most still aren?t. The UL category code for Division 2 motors is PTHE. UL Subject 1836, "Outline of Investigation for Electric Motors and Generators for Use in Class I, Division 2 and Class II, Division 2 Hazardous (Classified) Locations,? lists the basic requirements.

Both ANSI/UL 674 and UL Subject 1836 defer to NEMA MG-1 for basic motor requirements and only address additional requirements necessary for applications in classified locations.

The NEC does require specific marking for motors though. See Section 430.7. Of specific interest to this discussion will be 430.7(A) (13). Where a motor is marked ?Thermally Protected'' the device must be used per NEMA MG-1 to maintain the temperature rating of the motor. Alternatively a motor may be marked ?OVER TEMP PROT?. Motors marked this way must also use the device provided.

In either case, if the device exists, it must be used, no matter what the location?s classification is. Of course, not all motors, will have these devices and it is prudent in specifications, to tell motor suppliers that they are not to be.

Edited to correct the spelling of Laszlo's name (VERY sorry).

 

[petersonra]

In either case, if the device exists, it must be used, no matter what the location’s classification is. Of course, not all motors, will have these devices and it is prudent in specifications, to tell motor suppliers that they are not to be.

I have seen lots of motors with thermistors in them that are never hooked up. It seems to be the default on many larger motors. Are you saying there is a code violation if the thermistor is not used? Nothing in the code requires it.

 

[rbalex]

This is another vague area. Usually, it would fall under Section 110.3(B). The problem is most "ordinary location" motors are not listed or labeled. However, in the case under discussion, the motor is listed so the NEMA MG-1 (and UL) requirements are directly enforceable.

 

[petersonra]

This is another vague area. Usually, it would fall under Section 110.3(B). The problem is most "ordinary location" motors are not listed or labeled. However, in the case under discussion, the motor is listed so the NEMA MG-1 (and UL) requirements are directly enforceable.

I can't recall any motors that came like this that I have used where the instructions stated it was mandatory to use the thermal protection.

 

[rbalex]

I can't recall any motors that came like this that I have used where the instructions stated it was mandatory to use the thermal protection.

I can't say what instructions you have received, but if the motor was marked “thermally protected” or “OVER TEMP PROT,” I’ll bet it was buried in the instructions somewhere.

Edit add: I should note some devices directly interrupt internal winding conductors and may not need a control circuit interface.

 

[weressl]

I can't recall any motors that came like this that I have used where the instructions stated it was mandatory to use the thermal protection.

Integral thermal devices on motors for Division 1 areas must be connected to the control circuit for the UL/FM approval to be valid.

On small, single phase motors the "clixon" is wired into the leads so it will stop the motor dead when it overheats. they often use this on plug-in type equipment where external motor overload protection is not provided. (I have a vaccum cleaner that works this way.) These are "thermally protected" motors.

On small single phase motors sometimes they provide a "clixon" lead that is available for overload protection so you don't have to provide one, just wire this into the control circuit.

Some canned pump manufacturers provide embedded temperature switches that they request to be wired into the control circuit. These are 3 phase, larger motors.

As we slowly drift toward electronic controllers, both for speed control and energy savings I envision the thermistor electronic protection of the winding to be come the standard as a non-sinusodial current curve is extremely difficult to thermaly simulate with resistance element only as you get a lot of magnetic heating.

Just like the incandescent bulb the contactor eventually will become obsolete.