Motor space heater disconnection

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GamecockEE

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I have a project where the client currently has a number of 4160v motors which derive the power for the motor space heaters from the control transformers located in the motor starters. Therefore ZES at the motor is currently achieved by locking out the main power disconnect at the motor starter. The client would like to now feed the motor space heaters from a separate distribution panel. My concern is disconnecting the motor from all sources of power. My interpretation of 430.113 leads me to believe that a disconnect would need to be added in the field achieve compliance with the NEC. Am I missing anything here? any industry exceptions to the main rule?
Thanks in advance for your insight!
 
GamecockEE said:
I have a project where the client currently has a number of 4160v motors which derive the power for the motor space heaters from the control transformers located in the motor starters. Therefore ZES at the motor is currently achieved by locking out the main power disconnect at the motor starter. The client would like to now feed the motor space heaters from a separate distribution panel. My concern is disconnecting the motor from all sources of power. My interpretation of 430.113 leads me to believe that a disconnect would need to be added in the field achieve compliance with the NEC. Am I missing anything here? any industry exceptions to the main rule?
Thanks in advance for your insight!
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430.113 Energy from More Than One Source. Motor and
motor-operated equipment receiving electrical energy from
more than one source shall be provided with disconnecting
means from each source of electrical energy immediately adjacent
to the equipment served. Each source shall be permitted
to have a separate disconnecting means. Where multiple disconnecting
means are provided, a permanent warning sign
shall be provided on or adjacent to each disconnecting means.
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Are the heaters a motor or motor operated equipment?
 
The way you ask that question the answer is no. Motor heaters are not the motor or the motor operated equipment. However they are built into the motor, and require disconnection from the power source that serves them. What about other examples, such as field power for synchronous motors?
 
GamecockEE said:
The way you ask that question the answer is no. Motor heaters are not the motor or the motor operated equipment. However they are built into the motor, and require disconnection from the power source that serves them. What about other examples, such as field power for synchronous motors?
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field power feeds the motor. so do the devices that feed a small amount of juice into the windings to warm them up. this is neither.

I agree they require a disconnecting means, I am just not sure the section you cited is relevant in this particular case as to where the disconnecting means need to be located. There would be no harm in doing so, other than the cost.
 
Motor heater conductors terminate in the motor junction box. They should be on when the motor is off, and off when the motor is running.
The best and safest way to accomplish this is using the motor starter aux contacts. Or programmed off in a VFD when motor is stopped. VFD's have output relays that can be configured for this purpose.
I would not feed them from another source unless the power to the heaters will be disconnected when the motor is stopped.
A disco for the heaters does not make much sense.
You must make certain that power will be removed from the heaters when you lock out that particular motor.
Since these heaters are designed to be energized while the motor is stopped, it very easily becomes a saftey issue.
Motor windings are not used for this purpose. The heaters are completely seperate from the motor, but are attached to the outside of the motor stator winding in pairs.

Bob, Field power only exist's in DC motors. There is no such thing as a 4160 DC motor. AC motors do not have field windings, they have stator windings. No power is applied to ac motors that are stopped. Unless you have a VFD that is designed for full torque at stop.
 
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Thanks for your input. I agree with you folks and worry about the space heaters being fed from a separate source from a ZES standpoint which is required of course for motor changeouts. A synchronous motor does have a field circuit, that is what pulls it into synchronism with the AC power source. Manipulating the field excitation will allow the sync. motor to supply leading or lagging current into the AC system for power factor correction purposes.
My NEC handbook suggests that this section would apply to motor service ckts, but I can see some of your viewpoints in adhering to a strict reading of this Code Section.
 
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