Supplemental Nameplate for Motors with Upstream Speed Control

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emu44

Member
Location
Jacksonville, FL
Occupation
Mechanical Engineer
I have a fan replacement (Commercial HVAC) project where a customer requires motor redundancy, so they are going with ECMs. We are limited on amp draw due to their existing electrical architecture. The selection of EC Fans that we want to use gives the good reliability (redundancy) but at the cost of a higher overall FLA due to the extra motors, slightly too high for their electrical architecture. For the chosen EC Motors, they just require a 0-10V speed signal for modulation, no upstream VFD required.

This specific operating point they will be at does not require the motors to ever modulate more then 75%, even on a failed motor scenario, so the nameplate values will never be hit. This means that the actual amp draw would never be more than what their building can handle. We have the ability to limit the speed signal upstream to all motors via firmware so that we never send more then 7.5V.

The EC fan manufacturers already have a firmware limit inside of their motor controls in the motor itself that limits the performance and determines the OEM nameplate values. If that firmware limit is now upstream of the motor, does that mean we can/cant put a new nameplate on the motor?

In order to provide the required redundancy without having to rip out the existing architecture, could we put on a new nameplate on the motors that have the speed control limit applied? The motor manufacturer would have the ability to reflash the onboard firmware with new speed limits, but we have the capability to limit the speed on our own.

I cant find anywhere in the NEC that discusses software/firmware limitations on motors, maybe someone can point me in the right direction.
 
You cannot relabel the motors.

If half the motors are just for redundancy, you can arrange it so only one can run simultaneously and only count one of them in your load calculations.
 
petersonra said:
You cannot relabel the motors.

If half the motors are just for redundancy, you can arrange it so only one can run simultaneously and only count one of them in your load calculations.
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Our plan was to run all of the motors at the same speed for lowest possible power consumption, instead of half at a higher speed. You're saying if we had an interlock that made sure certain motors wouldn't run if a certain subset was powered, then we could rate using the smaller set of motors?
 
ptonsparky said:
What are the actual values in total that will be added to the existing service? Are you indicating that it is possible all the motors will operate at the same time? Can you make that impossible via control?

I doubt you can relabel anything but you can limit what operates and when.
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Yes, all of the motors would operate together at the same, low speed for lowest possible power consumption. We can make it impossible for a speed signal to be greater than a certain 0-10V when connected to our controller. It would be flashed onto a controller upstream without the ability for post-install limit adjustment by the customer.
 
emu44 said:
Yes, all of the motors would operate together at the same, low speed for lowest possible power consumption. We can make it impossible for a speed signal to be greater than a certain 0-10V when connected to our controller. It would be flashed onto a controller upstream without the ability for post-install limit adjustment by the customer.
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There is no provision to allow this in the load calculations.

What you might be able to do is take advantage of the NEC provision that allows you to measure the existing load instead of using the calculations when you add loads.
 
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