Portable Equipment in Haz Location

[schererguy]

Im using a portable mixing vessel in a Class 1 Div 2 location with SO cord and
Killark plug.
The xp motor has thermal switches connected in series inside the motor case.
Is it necessary to use these thermal switches on portable equipment?
Are there any Class 1 Div 2 plugs and outlets that have extra contacts for the thermal switches?
There is an inverter installed outside the room that controls the motor speed,
is it proper to use the thermal switches to disable the inverter when the motor reaches its high temperature or do I have to install a contactor between the motor and inverter because the inverter will hold a charge even after it is no longer enabled?

 

[rbalex]

The motor's explosionproof rating depends on the thermal switches; however the switches should interrupt the windings directly with no external connections.
Is the motor inverter rated? That is a NEMA MG-1 requirement for explosionproof motors and is recommended for any motor in classified locations.
Note: Most three-phase motors are not required to be explosionproof in Class I, Division 2.

 

[schererguy]

Yes the motor is inverter rated.
The three thermal switches are in series so only two wires come out to be wired.The motor label shows them going to the coil of a relay.
Do the motors with individual thermal sensors have six wires coming out to be wired in series with each phase?
If so isnt it likely that one of them will open first causing the motor to single phase until the others open?
Is it because over temperature is an extreme condition and not part of normal operation that this would be acceptable as protection.
Thanks so much for your response.

 

[don_resqcapt19]

The motor's explosionproof rating depends on the thermal switches; however the switches should interrupt the windings directly with no external connections.
Is the motor inverter rated? That is a NEMA MG-1 requirement for explosionproof motors and is recommended for any motor in classified locations.
Note: Most three-phase motors are not required to be explosionproof in Class I, Division 2.

Bob,
I have seen a number of motors used in Class II locations and a few in Class I where the internal thermal device was only suitable for use in the control circuit. I don't recall if these motors were marked for use in the Class II areas.

 

[rbalex]

Bob,
I have seen a number of motors used in Class II locations and a few in Class I where the internal thermal device was only suitable for use in the control circuit. I don't recall if these motors were marked for use in the Class II areas.

Originally, I inferred the motor was fractional hp, single-phase, since it was a mixer and single-phase motors are usually the only motors that are required to be explosionproof in Class I, Division 2. That is the class of explosionproof motor where the temperature switch is usually an inline device. Larger motors do indeed need to have their temperature switches in the control circuit as both schererguy and you mentioned. An inline switch usually can’t handle motor inrush currents or open the winding circuit at operating currents. While VFD operation would generally limit inrush, opening on over-temperature would still be a problem since the relevant circuit inductance is downstream of the VFD and severe arcing would occur.

If the motor is three-phase, that does change things a bit. As I noted earlier, it probably doesn’t need to be explosionproof. However, since it is, that introduces a new wrinkle; it is almost certainly UL listed and this is where it gets hairy. The temperature switch is integral to maintaining the motor’s rated “T-Code” - especially in inverter duty since harmonics can do nothing but produce heat. In Class I, this applies to both Division 1 and 2 motors. While explosionproof motors are acceptable in Division 2, the requirements of their listing still can’t be ignored.

There is a possible option. If the motor manufacturer can document and provide a nameplate for the motor’s “T-Code” in inverter duty without the temperature switches, there should be no problem assuming the “T-Code” is compatible with the area classification.

 

[plugman]

Haz Loc Plugs and Rec.

Haz Loc Plugs and Rec.

Im using a portable mixing vessel in a Class 1 Div 2 location with SO cord and
Killark plug.
...

Are there any Class 1 Div 2 plugs and outlets that have extra contacts for the thermal switches?
...

Meltric has their DXN series of plugs and receptacles that are Class 1 Div 2 rated and are available with auxiliary pilot contacts in 30A and 60A sizes.