Sine wave sensing isolation in NEC

[DickIllyes]

I need to sense the sine waves of several 240vac loads using a microprocessor.

I plan to use the Texas Instruments AMC1311 High-Impedance Isolated Amplifier and create a small PC board that will mount near each relay switching the loads on and off. This is part of a larger project to monitor some processes with microprocessors.

Where in the NEC is this covered? Does anyone have any thoughts on this requirement?

Thanks.

 

[electroman00]

Where in the NEC is this covered?

NEC says "shall be listed"...

Does anyone have any thoughts on this requirement?

What is the requirement??!!??

 

[gar]

191101-1301 EDT

Dicklllyes:

I really do not understand your question.

Apparently you have some sort of loads. Probably 120 V 60 Hz nominal, but possibly not. What power level are the loads? How does load current vary with time? What are you to measure? For example the instantaneous value, average value of some sort averaged over some period of time, RMS, or something else of something (voltage, current, power, reactive VA, peak, transients, harmonics, or whatever)?

In what way would you expect the NEC to apply?

.

 

[ron]

I need to sense the sine waves of several 240vac loads using a microprocessor.

I plan to use the Texas Instruments AMC1311 High-Impedance Isolated Amplifier and create a small PC board that will mount near each relay switching the loads on and off. This is part of a larger project to monitor some processes with microprocessors.

Where in the NEC is this covered? Does anyone have any thoughts on this requirement?

Thanks.

The Texas Instruments AMC1311 is a 2V input product.

The NEC is not a design standard. It is a code for minimum safety. The Texas Instruments AMC1311 is not for installation directly connected to 240Vac loads.

You likely want to use a standard test oscilloscope type meter with a data output so you can have the data you want without catching anything on fire.
Consider one of the Fluke Power Quality Analyzers for example. https://www.fluke.com/en-us/products/electrical-testing/power-quality-analyzers

 

[GoldDigger]

Whatever else you do, the sensing circuitry will need to be protected against overcurrent if it or its wiring fails. A small fuse is typically used for this purpose, often an inline fuseholder in the supply wiring.

You did not say whether you will be sensing just the voltage or the current also.

 

[Jraef]

Why are you specifically saying "sine waves"? Are you wanting to monitor power quality? If so, you can buy Power Quality meters that can be permanently installed on panels and connect to standard industrial networks like Ethernet, Modbus, Profibus etc. No need to reinvent the wheel.

 

[Besoeker3]

I need to sense the sine waves of several 240vac loads using a microprocessor.

I plan to use the Texas Instruments AMC1311 High-Impedance Isolated Amplifier and create a small PC board that will mount near each relay switching the loads on and off. This is part of a larger project to monitor some processes with microprocessors.

Where in the NEC is this covered? Does anyone have any thoughts on this requirement?

Thanks.

Exactly what aspect do you need to sense?

 

[paulengr]

Wouldn’t it be easier to buy a current relay from Carlos Gavazzi? This gives you direct digital output when current exceeds a threshold setting for instance. Commonly used to detect “machine running” of for custom protective relay functions on older gear. If you need current use a current sensor with a 4-20 mA output from say Automation Direct and just read that signal if you want analog? If you insist on voltage put a 250 ohm precision resistor across the voltage inputs (V=IR).

Reading raw currents is usually done with a shunt where the shunt (precision very low resistance usually specified as say 1 mV per A) connects to an optically isolated input to an ADC then you can sample at sub cycle rates but this is the circuitry used in protective relays, VFDs, etc. The shunt is commonly used in DC equipment and can be Listed on its own. The assembly is Listed for that type of equipment, UL61010 covers instrumentation. Shunts have very low reactance so kilohertz sampling rates or higher are easily achievable which can be used to detect for instance surges or ringing oscillations.

Generally speaking unless you manufacturing equipment the easiest way to comply with UL is to buy assemblies that are already Listed and do what you want. Buying components to build an assembly is strictly for experimental or R&D work where ultimately it gets submitted as an assembly to be Listed or never makes it out of the experiment. As a case in point the shop I work at is UL Listed for motors. We cannot use shop wiring, lugs, or most of their components for field work because it is part of Listed assemblies but not Listed on its own.

 

[paulengr]

Might want to look at National Instruments too. They have a ton of PC interface boards where for instance you just connect it to USB and it supplies all the IO. Also in DC drive work lots of guys use Windaq which interfaces well and directly supports a variety of input ranges. Again shunts are your friends as are various input modules.

Even in troubleshooting often we have to get creative with available equipment when it comes to things like taking voltage readings at say 12.47 kV or testing BIL. By the way I’ve seen a 2 million Volt BIL tester in operation up close. When it discharges...wow. It’s essentially a lightning simulator.

 

[electroman00]

Suggest all above to re-read the OP !!

Start with this line...

I need to sense the sine waves of several 240vac loads using a microprocessor.

The object of the game here isn't to confuse someone who is obviously already confused !!

That is not how you help someone...especially in the technical world of electrons !!

 

[hbiss]

Suggest all above to re-read the OP !!

Start with this line...



The object of the game here isn't to confuse someone who is obviously already confused !!

That is not how you help someone...especially in the technical world of electrons !!

All I can say is that some engineers don't express themselves in a way that makes you confident that they know what they are talking about. This guy might not have a clue or maybe he does. Doesn't matter though because he is asking if something that is not tangible at this point is subject to the NEC. Without at least an actual design there is no way of telling. Likely the finished product will require UL certification which will mean that you need to meet their standards which will include any NEC requirements.

-Hal

 

[paulengr]

All I can say is that some engineers don't express themselves in a way that makes you confident that they know what they are talking about. This guy might not have a clue or maybe he does. Doesn't matter though because he is asking if something that is not tangible at this point is subject to the NEC. Without at least an actual design there is no way of telling. Likely the finished product will require UL certification which will mean that you need to meet their standards which will include any NEC requirements.

-Hal

Funny. UL 809 and 809A are “mini NEC”. They read like the UL guys took NEC and started crossing out everything unrelated to

 

[electroman00]

All I can say is that some engineers don't express themselves in a way that makes you confident that they know what they are talking about. This guy might not have a clue or maybe he does. Doesn't matter though because he is asking if something that is not tangible at this point is subject to the NEC. Without at least an actual design there is no way of telling. Likely the finished product will require UL certification which will mean that you need to meet their standards which will include any NEC requirements.

-Hal

Again...Suggest all above to re-read the OP !!

All I can say is that some engineers don't express themselves in a way that makes you confident that they know what they are talking about.

I'm happy to say that...that is Your Bullpoop opinion...iow I read between the lines and you're not an Engineer.

This guy might not have a clue or maybe he does.

Well I certainly wouldn't go as far as to insult him !!!!
I said confused...as everyone is allowed to be confused regardless of status.

Doesn't matter though because he is asking if something that is not tangible at this point is subject to the NEC.

small PC board that will mount near each relay switching the loads on and off.

He's made it clear he wants to connect to something 240vac...and therefore is subject to NEC as I eluded to.

Without at least an actual design there is no way of telling.

Then why are you and everyone else "telling" in more words then not.

Likely the finished product will require UL certification

Thus...I quote...myself...
NEC says "shall be listed"...
Which is as broad in scope as the OP !!

which will mean that you need to meet their standards which will include any NEC requirements.

JFYI...your assertions in YOUR statement are by no means accurate !!

 

[electroman00]

Funny. UL 809 and 809A are “mini NEC”. They read like the UL guys took NEC and started crossing out everything unrelated to

An example please !!

 

[paulengr]

An example please !!

Example the ampacities are the 60 degree column only. 75, 90, etc.., are dropped.


Sent from my iPhone using Tapatalk

 

[winnie]

To the OP: the NEC doesn't really address this directly. The NEC requires that various connected components be 'listed', or 'suitable' or whatever. Your measurement tool is like a toaster; the NEC won't tell you how to make it; instead the NEC will require that it be 'listed' and then you would need to look at the various UL standards or engineering standards to figure out how to build a suitable tool.

It looks like paulengr pointed you to a possible UL standard for such an instrument...though if you are only building a few of these I'd bet that buying the standard book would be more expensive than simply buying appropriately rated/listed instruments.

The AMC1311 is an 'isolation amplifier', designed to take a 2V input signal but with several KV of isolation between input and output. This means, for example, that you could measure the millivolt signal across a current shunt resistor where that resistor is 'floating' at 120V to ground. IMHO the biggest problem with something like the AMC1311 is that you need to provide an isolated power supply for the measurement side. If the goal is to measure _current_, then I generally use something like a 'closed loop hall effect current transducer'; something such as https://www.digikey.com/product-detail/en/lem-usa-inc/LTS-25-NP/398-1002-ND/409815 The benefit here is that you are measuring the magnetic field developed around an insulated conductor, so you don't have any direct galvanic connection to the circuit being measured. You don't need a floating power supply, and the output is power limited by your instrument power supply. Similar but cheaper (and lower accuracy) systems work with open loop hall effect sensing or magneto-resistive sensing.

-Jon

 

[Besoeker3]

Interesting that the OP hasn't come back with more detail.

 

[hbiss]

Again...Suggest all above to re-read the OP !!

All I can say is that some engineers don't express themselves in a way that makes you confident that they know what they are talking about.

No engineer is going to say "I need to sense the sine waves..." So either he's dumbing it down for us or he doesn't know himself.

And no, I'm not an engineer. Are you??

-Hal

 

[paulengr]

No engineer is going to say "I need to sense the sine waves..." So either he's dumbing it down for us or he doesn't know himself.

And no, I'm not an engineer. Are you??

-Hal

Yes.

And if your background is programming you’d go towards the “obvious” solution because whatever you are building is already 95% software. Hardware is “simple”. But such a solution could be doing spectrograms and looking at harmonics too. There are a bunch of problems though. The raw analog interfacing. Buffering data too since the ADC is going to generate a sample at regular intervals but the CPU might be off doing other things. And building it to meet Listing requirements and sending samples to the Listing agency for testing. It is a huge job for what seems very simple to do if you work on the software side not hardware.

 

[Dennis Alwon]

There are a few articles that might apply but article 647 is for sensitive electronic equipment derived from a separately derived system. It may not apply IDK.

647.1 Scope. This article covers the installation and wiring of
separately derived systems operating at 120 volts line-to-line
and 60 volts to ground for sensitive electronic equipment.