What is "nonsinusoidal"?

[George Stolz]

Help me out here. I am looking at the 2011 NEC Draft, and confused by the following:

680.13 Voltages for Wet Contact. Requirements of this article recognized for an operating voltage of 15 volts or less and for an operating voltage of more than 15 volts are based the assumed use of sinusoidal ac. Where the supply source is other than sinusoidal ac, the following wet contact voltage values shall apply instead of 15 volts sinusoidal ac:
(1) 21.2 volts peak for nonsinusoidal ac.
(2) 30 volts for continuous dc.
(3) 12.4 volts peak for dc that is interrupted at a rate of 10
to 200 Hz.

Now, I am just a dumb electrician, so I would appreciate if the responses are tailored in such a way that I can understand.

What does this section mean?

Having nowhere else to turn, I've googled "nonsinusoidal" and realized that it is refering to a sine wave that has been altered in such a way as to be "un-sine-wavy". What normal processes are used to achieve this result intentionally in a pool setting?

Does a Class 2 transformer alter a sine wave?

Thanks in advance,

 

[Jljohnson]

I think the word may be akin to " Un-Stolz" but I am not sure myself. I'll be watching for the correct answer coming soom to Mike Holt's forum I am certain.

 

[iwire]

Having nowhere else to turn, I've googled "nonsinusoidal" and realized that it is refering to a sine wave that has been altered in such a way as to be "un-sine-wavy". What normal processes are used to achieve this result intentionally in a pool setting?

Think of an electronic power supply, it very likely puts out an "un-sine-wavy" voltage.

A transformer will put out the same wave going into it.

 

[nakulak]

non sinusoidal refers to triangular, sawtooth, square, clipped, and other waveforms, since the inherent power calculation for circuits driven by these voltage waveforms would not be correct (enough) using rms approximation, which is why they are pointing out a different value to use for the examples given. I hope that makes sense.

 

[iwire]

since the inherent power calculation for circuits driven by these voltage waveforms would not be correct (enough) using rms approximation, which is why they are pointing out a different value to use for the examples given. I hope that makes sense.

That makes perfect sense, thanks!

 

[jumper]

What normal processes are used to achieve this result intentionally in a pool setting?

Here is what I found:

Section 680.13:
This revision expands 15-volt AC low voltage limit for pool lights. Now includes DC and NOn-sinusoidal A.C, in accordance with Chapter 9 Table 11(A), 11(B) referencing "wet contact voltage values." This will permit new lighting methods for pools to include LED, which require voltage other than 15-volt AC.

here:
http://www.neca-neis.org/newsletter/report.cfm?articleID=9788

and I thought that this was interesting:

http://www.iaei.org/magazine/?p=2290

along with this:

http://www.rkw-consulting.com/LEDRulesHandout2.pdf

It seems that the code addition is in regards to LED lighting in pools.

 

[Besoeker]

Now, I am just a dumb electrician, so I would appreciate if the responses are tailored in such a way that I can understand.

Dumb? I think not. Your posts suggest very much the reverse.

Your description "un-sine-wavy" is a nice qualitative description. It's distortion of a sine wave. Almost every electronic device takes non-sinusoidal current from the supply. This, in turn, results in distortion of the supply voltage to a greater or lesser extent. Here's an example of actual measured voltage and current at my incoming supply:

The voltage, as you can see, resembles a sine wave. The current is nothing like one. It is distinctly non-sinusoidal.

What causes it?
Well, pretty much anything with an electronic power supply. At the time I made this measurement* the only items power up were the television(s), the computers, monitors, printers, possibly a few wall wart chargers and the refrigerator. All of these have electronic power supplies. These, collectively, took the current you see above. Horrible.

It is not achieved intentionally. The supply distortion is a consequence of the sheer volume of televisions, computers etc. I don't know about your pool setting but maybe that also uses a SMPS?

 

[jumper]

Geez, you engineers have some cool toys.:grin: Nice graphics.

 

[Besoeker]

Geez, you engineers have some cool toys.:grin: Nice graphics.

Thank you...I think.
Downloaded from a fairly regular digital oscilloscope.
The Excel is just my attempt to make it presentable.

 

[jumper]

Thank you...I think.
Downloaded from a fairly regular digital oscilloscope.
The Excel is just my attempt to make it presentable.

Yes it was a compliment, I find it a lot easier to understand certain things if I can actually see them.

 

[George Stolz]

Thanks for the replies, guys, I understand why the voltages would differ now, from one system to another. Now, my thought is, how can this be written to match the rest of the code book?

I think maybe it should have been drafted as a definition.

 

[cadpoint]

Thanks for the replies, guys, I understand why the voltages would differ now, from one system to another. Now, my thought is, how can this be written to match the rest of the code book?

I think maybe it should have been drafted as a definition.

Did you look at the origin of that code article? It could well be something
like a partical phrasing from IEC, ANSI, UL.

They know that the situation exists and made light of it through a Code article, I'm just posting outload... I don't know...

 

[cschmid]

Dumb? I think not. Your posts suggest very much the reverse.

Your description "un-sine-wavy" is a nice qualitative description. It's distortion of a sine wave. Almost every electronic device takes non-sinusoidal current from the supply. This, in turn, results in distortion of the supply voltage to a greater or lesser extent. Here's an example of actual measured voltage and current at my incoming supply:

The voltage, as you can see, resembles a sine wave. The current is nothing like one. It is distinctly non-sinusoidal.

What causes it?
Well, pretty much anything with an electronic power supply. At the time I made this measurement* the only items power up were the television(s), the computers, monitors, printers, possibly a few wall wart chargers and the refrigerator. All of these have electronic power supplies. These, collectively, took the current you see above. Horrible.

It is not achieved intentionally. The supply distortion is a consequence of the sheer volume of televisions, computers etc. I don't know about your pool setting but maybe that also uses a SMPS?

Nice capture and may I ask what the brand and model you are using..I can watch but not capture and transfer..I migh need to up grade some day..

Now are we going to start using terms like WET contacts in the NEC?? I always thought that was a slang term...

 

[augie47]

One can only assume the CMP came to the realization that 10% of the E/Cs and E/Is reading Art. 680 have begun to understand it and they could not allow that to happen.
seriously a 680 CMP member tells me they have a real problem trying to keep that Article current with new pool & lighting technology.

 

[Besoeker]

Nice capture and may I ask what the brand and model you are using..I can watch but not capture and transfer..I migh need to up grade some day..

We have a few Tektronix oscilloscopes. Most have a serial port so that you can download data directly to your PC. Assuming it has a serial port and many don't these days. In any case, I don't much care to have a direct connection between my laptop and a power circuit.
My favored weapon of choice is my old TDS360.

 

[zog]

Thanks for the replies, guys, I understand why the voltages would differ now, from one system to another. Now, my thought is, how can this be written to match the rest of the code book?

I think maybe it should have been drafted as a definition.

What? "Un-sine-wavy"?

 

[SAC]

There are a number of applications where AC or DC is "chopped", producing something more like a square wave. This is done because the width of the pulses can easily be controlled by a circuit (vs. controlling the amplitude), resulting in efficient control over the average power delivered to the load. This is a very common practice for controlling the brightness of LEDs, though it also works with typical incandescents, as well.

 

[76nemo]

You can easily find richer harmonic loads with an averaging meter compared to a meter that's true RMS, but that's old school compared to what you can see with a scope

 

[George Stolz]

What? "Un-sine-wavy"?

No, the new section I quoted. It looks like a definition, sort of; only it's not in the xxx.2 section of it's article, and it's wording is poor, IMO.