Need Help with Electrical Portion of New design

[Hank Mead]

My company is Thermal Interrupt devices and we have a patented design for a device that prevents centrifugal pumps from overheating due to loss of prime or blocked intake/discharge piping. The device is screwed into the pump housing with 1/4" MPT and wired into one of the hot leads of the pump motor. Typical applications are swimming pool pumps, spa pumps, above ground irrigation pumps, de-watering pumps and various types of submersible pumps. We have several designs for different applications from 110 v up to 240 v 3-phase.

When the device detects a pump temperature of 120 F, the electrical contacts open and power is interrupted to the pump motor, thereby saving the pump from destruction due to overheating. The device must be reset either manually or remotely by a technician or by a knowledgeable homeowner. The device is not to be used or considered as a normal on/off switch and the warning label states that the main power to the motor be disconnected before attempting to reset the device.

The device is water resistant, mostly plastic with no conductive material connecting the internal electrical contacts with the metal threaded base. The electrical contacts are approximately 1.5" away from the threaded metal base and are contained in a separate, non-conductive housing to which the 14 AWG leads are attached and are lead out of the device through waterproof fittings.

Now for my questions (finally!):
1. Will this device require a ground wire? If so, why?
2. For 240 v applications will we have to break both hot leads or can we just break one? Again, this device is not intended to be a fuse, breaker or normal on/off switch.

Thanks in advance!


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[chris kennedy]

Welcome to the Forum Hank.

Could you supply a link to the specs for this device?

 

[cadpoint]

I’ve got a few questions? Can we consider it Equipment, Article 100?

If this is the case is it double insolated?

Read all of 250.110 very closely, if it is double insolated then you bettered that by an exception.

But let’s go backward.

110.54 you don’t have one from the start so 250.110 is your ride.

But I have a problem with the design you said 14 AWG, is that the same size every time to all applications? don't forget 110.15 (C) and (C)(1).

110.9 Interrupting Rating, Is that what your device is doing? Frankly, I don't know.

or

100. Switch Motor-Circuit, this thing do that?

In the end 110.3 might be the catch all, in respects to you application?

And of course is it Listed and Labeled, Article 100?

Oh I'm sure that there are plenty of other Articles in the NEC that I have not even addressed, yet, but ... But, since it's not a circuit breaker (as you stated), a circuit breaker is required to clear all ungrounded (live/hot) circuits.

 

[hurk27]

I'm having a hard time figuring out why would a centrifugal pump over heat in the conditions mentioned?

a blocked inlet, run out of water, cavation, will only unload the motor, thus the motor will pull less current and result in less heat, pump seals could be subject to damage, there are systems that even depend upon this feature of a centrifugal pump.

I also see a problem with pool pumps because many times they sit outside right in direct sun light, which could cause nascent tripping?

I have one question, are these going to be sold to the manufacture, or as an add on component?

both could effect the UL listing of the pump.