Article 725 - Class 1, 2, 3 Circuits Question - HELP

[chevywaldo]

I've been using my very old NEC book for 20 years or more. Now I just got a hold of a 2005 NEC book. Looking at Article 725, it completely changed, or so it appears. There used to be a table designating the maximum power, volts, amps, etc for each of the classes. that table is now gone. I read most of the article and I can't find anywhere where it states the criteria for Class 2 Circuits (volts, amps, inherently limited power, etc) Where does it explain what a Class 2 circuit is?

Again, I'm talking about the 2005 NEC book right now. I do not have the newer NEC books.

 

[iwire]

It is on page 70?639 (or at least it is in my pdf of it)

I think it was moved to the back with the tables as it is really not part of the code.

 

[don_resqcapt19]

It is on page 70?639 (or at least it is in my pdf of it)

I think it was moved to the back with the tables as it is really not part of the code.

The information is in Tables 11A and 11B in Chapter 9, so they are still part of the code. Not sure why they were moved from Article 725 to Chapter 9.

 

[chevywaldo]

It is on page 70?639 (or at least it is in my pdf of it)

I think it was moved to the back with the tables as it is really not part of the code.

thanks for the information guys. WOW. the code books really changed the last 10-20 years. My code book was so old I feel stupid now, waiting so long to look at a new code book. They really moved things around. And yes, it is now in the "TABLES" chapter on page 70-639 like you guys said. Thanks.

 

[kwired]

thanks for the information guys. WOW. the code books really changed the last 10-20 years. My code book was so old I feel stupid now, waiting so long to look at a new code book. They really moved things around. And yes, it is now in the "TABLES" chapter on page 70-639 like you guys said. Thanks.

Your profile says you are an engineer & contractor.

How have you survived without current code for areas you have worked in? Now if you do primarily industrial work, maybe you get away with it easier. Many changes that have happened that would effect that area were just editorial or relocation, but there has had to be a few things come up now and then that you can not do today that you could do 20 years ago, or even that you couldn't do 20 years ago and can do now.

If you do residential work... you are in the dark ages with a 20 year old code book. With a 2005, you may be past the dark ages but not by very far - unless you are in an area that is still on the 2005 as the standard - there probably is some areas that are.

 

[chevywaldo]

Your profile says you are an engineer & contractor.

How have you survived without current code for areas you have worked in? Now if you do primarily industrial work, maybe you get away with it easier. Many changes that have happened that would effect that area were just editorial or relocation, but there has had to be a few things come up now and then that you can not do today that you could do 20 years ago, or even that you couldn't do 20 years ago and can do now.

If you do residential work... you are in the dark ages with a 20 year old code book. With a 2005, you may be past the dark ages but not by very far - unless you are in an area that is still on the 2005 as the standard - there probably is some areas that are.

well lets see. 1st of all I'm a "project engineer", not a state licensed P.E. Big difference as you know. Also, our electricians (local 134) who install the drawings that I prepare, are "supposed" to know the NEC and Chicago code and modify the installation as needed to meet code and serviceability. Most of them don't know the code (not uncommon), but are still very good electricians. We do commercial only, no residential. Most of the work we do is controls, no power or power distribution. Most work we do is Class 2. Most if not all the transformers we use, you can hold in your hand, or if they are larger ones (500VA) are broken out into multiple Class 2 circuits (with built in secondary overcurrent protection).

Having said all that. I still need and want an understanding of the code for transformers because I'm trying to find out if we "need" to install overcurrent protection on both the Primary and Secondary sides of all the transformers we install. Right now on some jobs we do not, and I don't know if we are meeting code or not.

 

[chevywaldo]

More XFMR Overcurrent Protection Devices Questions

More XFMR Overcurrent Protection Devices Questions

1) So if a transformer meets the requirements of Class 2, but is NOT listed as
"Class 2", is it a Class 2 device even though it carries no listing from the
mfr?
2) Is a transformer with no built in circuit breaker or overcurrent
protection considered an "inherently limited power source" ? I would think the
answer is no.

3) If the answer to #2 above is "NO", then per table 11(A), if a transformer
is 120/24 VAC, then per table 11(A) the maximum overcurrent protection is
100/Vmax = .83 amps (primary side). Is this correct?

4) If #3 above is correct, is "secondary" overcurrent protection required?
See table 450.3(B). I think the answer is NO.

5) Can anybody answer this question: When is "primary and secondary
overcurrent" protection required for a transformer, and where in the code does
it state this?

 

[kwired]

1) So if a transformer meets the requirements of Class 2, but is NOT listed as
"Class 2", is it a Class 2 device even though it carries no listing from the
mfr?

2011: 725.121(A) and exceptions basically tells us all class 2 and 3 power supplies or transformers must be listed. A thermocouple is about the only source that doesn't need to be listed.

 

[GoldDigger]

2011: 725.121(A) and exceptions basically tells us all class 2 and 3 power supplies or transformers must be listed. A thermocouple is about the only source that doesn't need to be listed.

And just to nail it down, part of the listing requirement is that the device be marked accordingly.
So if it is not marked, it is not listed.

 

[ActionDave]

I'll give my answer thread.

 

[mike1061]

well lets see. 1st of all I'm a "project engineer", not a state licensed P.E.

Also, our electricians (local 134) who install the drawings that I prepare, are "supposed" to know the NEC and Chicago code and modify the installation as needed to meet code and serviceability. Most of them don't know the code (not uncommon),

Do you still wonder why electricians hate engineers?
We have to modify things because of field conditions, not correct mistakes in the drawings. We are counting on you guys staying up on the code. In fact I thought you guys take classes on code changes and new products. Some do, I've herd that from others. It's your job, wouldn't you want to stay up to date?

Please catch up with current code.
Thanks
Mike

 

[chevywaldo]

I'll give my answer thread.

I still like Rocky Mountain High for some reason. But don't tell my friends. And come on, White Wedding is a classic.

 

[chevywaldo]

Do you still wonder why electricians hate engineers?
We have to modify things because of field conditions, not correct mistakes in the drawings. We are counting on you guys staying up on the code. In fact I thought you guys take classes on code changes and new products. Some do, I've herd that from others. It's your job, wouldn't you want to stay up to date?

Please catch up with current code.
Thanks
Mike

Yes I agree, we need to keep up with the code. And not all our electricians "hate" us engineers, because we are often on the jobsite with them, in the trenches so to speak, doing all we can to help them get their job done more efficiently and more effectively. We don't just sit in the office with white shirts and ties and pretend we are smarter or more valuable than they are - we are all team players and communicate well with one another and respect each others jobs. Neither of which are easy, especially in new construction.

 

[Smart $]

1) So if a transformer meets the requirements of Class 2, but is NOT listed as
"Class 2", is it a Class 2 device even though it carries no listing from the
mfr?
2) Is a transformer with no built in circuit breaker or overcurrent
protection considered an "inherently limited power source" ? I would think the
answer is no.

3) If the answer to #2 above is "NO", then per table 11(A), if a transformer
is 120/24 VAC, then per table 11(A) the maximum overcurrent protection is
100/Vmax = .83 amps (primary side). Is this correct?

4) If #3 above is correct, is "secondary" overcurrent protection required?
See table 450.3(B). I think the answer is NO.

5) Can anybody answer this question: When is "primary and secondary
overcurrent" protection required for a transformer, and where in the code does
it state this?

1) As noted by others, a Class 2 power source must be listed and so marked.

2) "No" is correct.

3) Not correct. The maximum overcurrent protection is in reference to the output of the Class 2 transformer, and V_MAX is 24V_AC: 100/24 = 4.17A through the secondary.

4) #3 is not correct, so question is rendered moot. If another answer is desired, please re-phrase the question accordingly.

5) All transformers require primary protection in one form or another. Typically, secondary overcurrent protection (for the transformer) is required when primary protection rating exceeds the value permitted for primary only protection (though I'm uncertain why required for "currents less than 2 amperes when primary rating is less than primary only rating). Note secondary protection required by Article 725 and associated Tables in Chapter 9 and Article 450 transformer secondary protection are two distinct compliance issues. However, one overcurrent device, or one set of devices as applicable, can establish compliance with both Articles.