help locating definitions for Class II & "low v

[vithoward]

I've been trying to locate a reference for "Class II" and "low voltage" in the NEC.

According to my 2003 CD text search, low voltage is

(1) less than 600 volts,
(2) equal to or less than 30 volts, and
(3) equal to or less than 24 volts.

I can't find a definition for the "Classes"

Are my glasses dirty? Is my search engine broken?
Is it under my nose and I just can't find them?
HELP!

 

[don_resqcapt19]

Re: help locating definitions for Class II & "low v

You need to look at Article 725.
Don

 

[vithoward]

Re: help locating definitions for Class II & "low v

Don, Thanks for the reply.

I've check 725. In the 2002 code, 725.21 addresses Class 1. I located a couple of tables in section 725.31 in the 1993 code, but they don't appear in the 2002 version.

According to what I find, there isn't a current definition for Class 2 or Class 3.

Howard

 

[don_resqcapt19]

Re: help locating definitions for Class II & "low v

Howard,
You are correct that the old definitions are gone. It is a Class 2 circuit if it is connected to a listed Class 2 power supply or listed equipment that is marked to identify it as a Class 2 circuit. The classification of the circuit type has been left up to the listing agency. See 725.41.
Don

 

[tony_psuee]

Re: help locating definitions for Class II & "low v

I'm glad I'm not the only one who has had difficulty determining circuit classification. I had a disagreement with an engineer I used to work with regarding a circuit's classification. We used a UL listed 24Vdc power supply to power some temperature sensors. His interpretation of NEC was that the circuit was class 2, even though it was powered from UL panel and NEC had to be applied. The power supply was not listed as class 2. However, in picking my battles, fused the output of the power supply per the OEM's recommendations, in addition to the electronic overload circuit integral to the supply, and labeled it as a Class 2 circuit. The interesting thing is the UL inspector of the panel had no position one way or the other. Of course what my colleague found out was now that it was a class 2 circuit he had to add a barrier to all junction boxes on the equipment in which class 1 wiring was present!

Tony

 

[vithoward]

Re: help locating definitions for Class II & "low v

Tony,

Thanks for your input. For the past several years, I have had the privilege of serving as a volunteer on a NICET committee that it establishing certification standards for closed circuit television installers and system designers. We have made several references to the importance of following code (NEC), and I was "volunteered" to locate the pertinent sections. I was really shocked to find that the definitions don't exist.

According to what's been pointed out to me, it's a class 2 circuit if it's connected to a class to power source. But, what's a class 2 power source if there is no definition? Can I build my own and label it "class 2?"

I tried to contact NFPA to discuss the lack of definitions, but since I'm not a member, no one was willing to talk to me.

Since we are trying to improve the quality of work thoughout our industries, it makes since to me that we should make it easy for neophites to read and interpret the code. It's very difficult for those of use with years of experience to find simple answers. What can we do to improve the situation? I don't want to ***** .... I want to help fix the problem!

Howard

 

[vithoward]

Re: help locating definitions for Class II & "low v

Sorry 'bout the type in the previouus post. Class to should be class two. Also since I can't use the word ***** , change it to complain.

 

[don_resqcapt19]

Re: help locating definitions for Class II & "low v

Howard,
You cannot build your own power supply and call it a Class 2 system, unless you get your homemade power supply listed. 724.41 requires the use of listed power supplies. I think that the possibility of someone building their own power supply is the very reason that the definitions have been removed from the code. Field assembled or "homemade" power supplies created an enforcement problem for the inspector. He had no real way of knowing for sure that the power supply did not exceed the permitted energy output. The requirement that it is a Class 2 system only if the power is supplied by a listed Class 2 power supply removed this problem.
Don

 

[vithoward]

Re: help locating definitions for Class II & "low v

Don,

Thanks again for your input. I was being facetious in my suggesting that I could build a Class 2 supply.

The point I was trying to make was, that without any guidelines, someone who was not already somewhat familiar with the topic would have no clue as to what kind of animal a class 2 would be. From experience I know that it is low voltage with a very limited amount of amperage. Someone looking at the NEC for the first time would have no idea what a class 2 was or what makes it different from class 1 or 3. Simply picking up a class 2 power supply doesn't answer the question either.

I found three different references to "low voltage".... less than 600 volts, 30 or less volts, and 24 or less volts. Again, to someone new to the code, it's conflicting and confusing.

I guess I'm sensitive to the low voltage side of the business, because all we do is cameras and low voltage communication wiring. Since, I'm also doing training, I would like to have a source for my explanations.

 

[tony_psuee]

Re: help locating definitions for Class II & "low v

Don,

Howard brings up the point that caused the confusion with me, there was not a clear definition of Class 2 circuit and it referenced three voltage levels. Other applications made it clear, with a class 2 supply , such as a 120/24Vac transformer. UL's position was the supply was not class 2, so it did not have to be designed in the panel as such and they are not concerned with what it is wired to it unless the final equipment is UL listed. The NEC gives examples in the handbook, 725.1, or power limited circuits. However, it is not all inclusive and does leave a grey area. Are temperature and pressure sensors powered by 24Vac or 24Vdc class 2 circuits if the supply is not listed as a class 2 device? I have some some components that state, "powered from class 2 listed source", but not all are such. Am I confusing the issue? I would greatly appreciate feedback.

Tony

 

[don_resqcapt19]

Re: help locating definitions for Class II & "low v

Tony,
If the power supply is not a listed Class 2 power supply, then the circuit is not a Class 2 circuit.

Class 2 Circuit. The portion of the wiring system between the load side of a Class 2 power source and the connected equipment.

725.41(A) Power Source. The power source for a Class 2 or a Class 3 circuit shall be as specified in 725.41(A)(1), (2), (3), (4), or (5)

Don

 

[tony_psuee]

Re: help locating definitions for Class II & "low v

Don,

Thank you very much. As I stated, I had always based it off the power source and not the device being powered. However, this gentleman chose to differ with his interpretation of the NEC and I couldn't provide him with sufficient evidence to change his point of view. Which has created this area of confusion for me until now.

Tony

 

[pierre]

Re: help locating definitions for Class II & "low v

Just as there is an ongoing issue with the neutral definition, there is some issue with the term 'low voltage'. What is low voltage? It really depends on who you are speaking with, a lineman thinks 600v and lower is low voltage, I have spoken to people who call 120v low voltage, and of course there is 12, 24, 32 low voltage. So what really is low voltage? Ten people will give ten different answers and all ten are correct. There is no such thing as 'low voltage', not until somebody comes up with a definition.

The dictionary defines low as - close to the ground. We already have enough problems with ground , that won't work. I do not have my IEEE dictionary here, but will look up their definition, if they have one.
Even Tom Henry's dictionary does not define low voltage.

Maybe low voltage should not have a definition, and we should qualify the voltage in our work. When necessary using the phrase 'limited energy systems' or 'limited energy' might be better, and over the next xxx years that can become the jargon we use instead.
Otherwise I have very little to say about this :roll:

Pierre

 

[hbiss]

Re: help locating definitions for Class II & "low v

Confused? Maybe it's because we are caught in the middle. Class 1, 2 and 3 audio wiring was the topic of a letter that I sent to Mike which he subsequently sent to everybody as a newsletter. If you haven't read it or don't remember it take a look here- http://www.mikeholt.com/news/archive/html/10/Audio_Wiring_for_Speakers_06-30-2003.htm

At least as far as the audio industry is concerned I get the impression that they don't want anybody like the NEC telling them how to wire their products. Hence there is a lack of cooperation between industries and a lack any information relating to such in their literature. Take a look at the responses to this newsletter here: http://www.mikeholt.com/onlinetraining/newsletter/userviewcomments.php?id=102003530105430

All the responses were positive or in agreement except for the sixth response from the "THX guy". Aside from the fact that he really doesn't know too much about what he's saying, it does pretty much sum up the attitude of the audio industry in regard to "oversight" by the electrical industry.

You have to admit that any amplifier that requires Class 1 wiring is not going to sell as well as one of comparable power and requiring Class 3 or 2 wiring. To play the devil's advocate, I would think that there is alot at stake here for manufacturers and installers if much of this stays uninforceable.

 

[pierre]

Re: help locating definitions for Class II & "low v

One of the things that I have learned(thats almost all of what I have learned ) over my years on earth is; when somebody rants the way the tdx guy did, he is usually upset that somebody is invading his private party and ruining what he has going on.
I would not want to work with him on a daily basis.
People are more apt to listen when you are professional and respectful.

Pierre

 

[mtm]

Re: help locating definitions for Class II & "low v

Amazing:
I just started using this site today. I have been pooring over the speaker wire issue for several days, trying to understand how it the NEC is to be interpreted, since no one makes speaker cable that meets class one spec's!
I have been making my own by twisting THHN for years. How about some manufacturers taking note of a potentially lucrative market!
Here's what we need: #12 and #10 Class one rated twisted-pair speaker cable.
Anything smaller than that probably isn't going to be connected to a class one amplifier anyway.

As for the THX Guy...try that in live sound! I have 1200watt power amps clipping on a regular basis, because the FOH engineer is deaf. This isn't limited energy!
:roll:

 

[hbiss]

Re: help locating definitions for Class II & "low v

Clifford ( cliffordvt.com ) will twist and put on reels TFFN and THHN in any of the sizes we are likely to need at a nominal cost. Did you really mean you are doing it yourself?

Plenty of amps out there that require Class 1 wiring that have constant voltage outputs (70.7 and 100 volts) These are often used with 18 or 16ga wire for distributed applications. I think somebody needs to come up with an 18 to 10ga product line.

I mentioned that I can't understand how these wiring requirements are actually determined. They are not dependant on output power. I've used Crown CT-810's that are 400W per channel and require Class 1 wiring. Now, I got a brochure a little while back from Bogen for their Black Max line. There is a picture (this is the only way you will find out what the wiring requirements are from their literature) of the back panel of the X600 which is 600W per channel. This is 70.7 volts which happens to be 8 ohms at 600W. The output is clearly labeled "Class 2 wiring acceptable". This is 50% more power and TWO steps down in wiring requirement than the Crown! Okay, I realize we are comparing Crown to Bogen but huhh?

As for the THX guy, if he understood a little bit more about what he is involved with he wouldn't be so quick to say there can be no hazard. 400, 600, 1800 watts, whatever, is considerable energy. Think about the possibility of a blown voice coil or an open line and the open circuit voltage can equal that of a 120 volt circuit.

One of my first jobs out of high school (about a million years ago) was an engineering tech for a company that made automated (about as automated as you could get in those days) test equipment. One system we made was for a railway signal manufacturing company that would test their contactors and relays. Some were quite large, most were oddball by our experience.

The drive for the coils of the device under test needed to be variable in both voltage and frequency. We used a Crown amp driven by a variable frequency sine wave source (simple audio generator). Even in those relatively low power and inefficient vacuum tube days that amp could supply up to something like 220 volts at enough current to do the job.

 

[pierre]

Re: help locating definitions for Class II & "low v

725.2 is the location of the definitions for Class 1, 2, 3.

Pierre

 

[hbiss]

Re: help locating definitions for Class II & "low v

As was stated, there is no definition for class 2 or class 3 only that the class depends on the class of the power source.

Class 1 (725.21) is totally obscure and is an area that needs to be rewritten or deleted to reflect current technology. No reason not to use the same method as for class 3 and 2- every power source is to be listed and labeled with the class of wiring required to be used with it. Many class 1 devices have always used this method.

As 725.21 is written now, it might be useful to the manufacturers of some electrical equipment (not too many contractors or inspectors have a bench full of test equipment) and is useless in determining the output requirement of something like an audio amp so it doesn't help at all. Obviously this is determined through some other method by UL anyway.

 

[daveb]

Re: help locating definitions for Class II & "low v

Several of the above messages indicated that there is no definition of a Class 2 power supply. But isn't the definition given in 725.41 (A), FPN No. 2, which states, "Table 11(A) and Table 11(B) in Chapter 9 provide the requirements for listed Class 2 and Class 3 power sources."?

But I have a question of my own: We are a manufacturer of Class 2 transformers and have been selling UL Recognized (i.e. "component-type") transformers to OEM's in the HVAC industry for many years. These are incomplete in certain details (i.e. the enclosure) which will be provided in the end-use application. But one of our customers has started complaining that our transformers are in violation of the NEC because they are not "listed" Class 2 power sources. Has anyone else ever heard this argument before?

It seems to me that this customer is confusing NEC's definition of "listed" with "UL Listed". Furthermore, Article 725.41 (A) (3) allows other listed equipment (i.e. the end product that uses the transformer) to house the Class 2 power source, which--in this case--does not itself have to be listed.

Am I correct, or am I missing something?