Explosion Proof Motor Question

[bobhudon]

I am using an inverter duty rated explosion proof motor with a variable frequency drive. Does the motor require a thermostat or other over temperature device to satisfy code?

 

[stew]

Re: Explosion Proof Motor Question

no overtemp or thermostat required just the normal overcurrent protection and thermal overloads in your starter.The vfd mag starter will come with overload protection.

 

[rbalex]

Re: Explosion Proof Motor Question

From NEMA MG-1 1998 (Bold added)

14.32 OPERATION OF ALTERNATING CURRENT MOTORS FROM VARIABLE-FREQUENCY OR VARIABLE-VOLTAGE POWER SUPPLIES, OR BOTH
14.32.1 Performance
variable-voltage power supplies, or both, for adjustable-speed-drive applications may require individual consideration to provide satisfactory performance. Especially for operation below rated speed, it may be necessary to reduce the motor torque load below the rated full-load torque to avoid overheating the motors. The motor manufacturer should be consulted before selecting a motor for such applications (see Parts 30 and 31).
WARNING: Motors operated from variable frequency or variable voltage power supplies, or both, should not be used in any Division 1 hazardous (classified) locations unless :
a. The motor is identified on the nameplate as acceptable for variable speed operation when used in Division 1 hazardous (classified) locations.
b. The actual operating speed range is not outside of the permissible operating speed range marked on the motor nameplate.
c. The actual power supply is consistent with the type of power supply identified in information which is supplied by the motor manufacturer.
For motors to be used in any Division 2 hazardous (classified) locations, the motor manufacturer should be consulted.
High frequency harmonics of inverters can cause an increase in the level of leakage current in the motor. Therefore, users are cautioned to follow established grounding practices for the motor frame.
Failure to comply with this warning could result in an unsafe installation that could cause damage to property, serious injury or death to personnel, or both.

These requirements are essentially repeated in the sections for fractional, integral and synchronous motors so I cited them from only one source.

Technically this is an 110.3(B) issue. stew is correct that no additional thermal protection is specified by the Code. The critical thing is that the motor manufacture has identified the motor as suitable for use in Division I with a variable speed drive and it is otherwise used consistently with 14.32.1 (or other relevant sections) and any MANUFACTURER requirements;i.e., they may specify (or provide) auxiliary thermal protection, in which case it would have to be used. Otherwise, it is not required.

 

[bobhudon]

Re: Explosion Proof Motor Question

Thanks for the quick response!

 

[stew]

Re: Explosion Proof Motor Question

Yes very important to know what the mfg says even if the unit is vfd rated. I agree completly.

[ June 25, 2004, 08:33 PM: Message edited by: stew ]