Class 2 wiring vs Class 3

[Dennis Alwon]

I was told by a wire company that if I could use class 3 wiring for the low voltage system that is rated class 2. Is this true?

 

[petersonra]

I was told by a wire company that if I could use class 3 wiring for the low voltage system that is rated class 2. Is this true?

there is a confusing matrix of wiring methods for class 2 and 3 wiring.

it seems like most of the stuff used in class 3 wiring can indeed also be used in class 2 wiring.

i can't recall ever doing any class 3 wiring though.

 

[Dennis Alwon]

there is a confusing matrix of wiring methods for class 2 and 3 wiring.

it seems like most of the stuff used in class 3 wiring can indeed also be used in class 2 wiring.

i can't recall ever doing any class 3 wiring though.

I have some cable - class 3 that i bought years ago for speakers-- 12/2. They say I can use it but the manufacturers of the product have no idea. I have never understood this class wiring

 

[guschash]

The only thing I could find was in the definition 725.2 class 3 circuit. It says C3 are permitted to have higher levels of voltage than C2.

 

[Dennis Alwon]

The only thing I could find was in the definition 725.2 class 3 circuit. It says C3 are permitted to have higher levels of voltage than C2.

That is exactly what I see so IMO class 3 can be used and I am going with it. I did talk to a very knowledgeable inspector in Durham who said the same thing.

Thank you

 

[dicklaxt]

Makes sense to me for what ever thats worth.

dick

 

[augie47]

If you found an inspector that understands all the nuances with Class 2 and 3 he is indeed "knowledgeable"

 

[don_resqcapt19]

The permitted cable substitutions are shown in Table 725.156(G). It is clear that a CL3 cable can be used anywhere a CL2 cable is required. There is also a figure that shows the substitutions.

 

[RB1]

Class 3 cable is permitted to be used for Class 2 wiring. CL3P is at the top of the heap. It can be used for any application of Class 2, or Class 3 wiring. There is no Class 3 cable within the same classification of use; i.e., plenum, riser, general purpose or dwelling that cannot be substituted for Class 2 cable within the same classification.

 

[Dennis Alwon]

Here is what I don't understand about this. I can run this class 3 wire thru the walls and connect to a low voltage system that does not have a wiring compartment- lights with tails sticking out or leads if you will. I can just use wire nuts however if I run NM cable, mc cable-- and do the same then it is a violation. At least that is my understanding

 

[petersonra]

Here is what I don't understand about this. I can run this class 3 wire thru the walls and connect to a low voltage system that does not have a wiring compartment- lights with tails sticking out or leads if you will. I can just use wire nuts however if I run NM cable, mc cable-- and do the same then it is a violation. At least that is my understanding

That is my understanding as well.

725.3 Other Articles. Circuits and equipment shall comply
with the articles or sections listed in 725.3(A) through
(J). Only those sections of Article 300 referenced in this
article shall apply to Class 1, Class 2, and Class 3 circuits.

This allows you to use chapter 3 wiring methods.

725.130 Wiring Methods and Materials on Load Side of
the Class 2 or Class 3 Power Source. Class 2 and Class 3
circuits on the load side of the power source shall be permitted
to be installed using wiring methods and materials in
accordance with either 725.130(A) or (B).
(A) Class 1 Wiring Methods and Materials. Installation
shall be in accordance with 725.46.

This requires you to follow chapter 3 rules if using chapter 3 wiring methods on a class 2 or 3 circuit.

725.46 Class 1 Circuit Wiring Methods. Class 1 circuits
shall be installed in accordance with Part I of Article 300
and with the wiring methods from the appropriate articles
in Chapter 3.

 

[Dennis Alwon]

Now the question is WHY????

 

[Dennis Alwon]

To clarify -- why can I make a free air splice with Class 3 wiring and not with NM cable which has a higher voltage rating.

 

[Speedskater]

What about?
725.130 Wiring Methods and Materials on Load Side of
the Class 2 or Class 3 Power Source. Class 2 and Class 3
circuits on the load side of the power source shall be permitted
to be installed using wiring methods and materials in
accordance with either 725.130(A) or (B).
(A) Class 1 Wiring Methods and Materials. Installation
shall be in accordance with 725.46.
Exception No. 1: The ampacity adjustment factors given
in 310.15(B)(3)(a) shall not apply. [ROP 6-53, 3-187,
3-188]
Exception No. 2: Class 2 and Class 3 circuits shall be
permitted to be reclassified and installed as Class 1 circuits
if the Class 2 and Class 3 markings required in 725.124 are
eliminated and the entire circuit is installed using the wiring
methods and materials in accordance with Part II,
Class 1 circuits.
Informational Note: Class 2 and Class 3 circuits reclassified
and installed as Class 1 circuits are no longer Class 2
or Class 3 circuits, regardless of the continued connection
to a Class 2 or Class 3 power source.

And then:
725.49 Class 1 Circuit Conductors.
(A) Sizes and Use. Conductors of sizes 18 AWG and 16
AWG shall be permitted to be used, provided they supply
loads that do not exceed the ampacities given in 402.5 and
are installed in a raceway, an approved enclosure, or a
listed cable. Conductors larger than 16 AWG shall not supply
loads greater than the ampacities given in 310.15. Flexible
cords shall comply with Article 400.
(B) Insulation. Insulation on conductors shall be rated for
600 volts. Conductors larger than 16 AWG shall comply
with Article 310. Conductors in sizes 18 AWG and 16
AWG shall be Type FFH-2, KF-2, KFF-2, PAF, PAFF, PF,
PFF, PGF, PGFF, PTF, PTFF, RFH-2, RFHH-2, RFHH-3,
SF-2, SFF-2, TF, TFF, TFFN, TFN, ZF, or ZFF. Conductors
with other types and thicknesses of insulation shall be permitted
if listed for Class 1 circuit use.

 

[Dennis Alwon]

Kevin I don't know the point you want to make.

 

[guschash]

Found it. 2011 Table 725.179Cable markings In the informational Note: .....and Class 3 cables are listed above Class 2 cables because Class 3 cables can substitute for Class 2 cables.

 

[Dennis Alwon]

Found it. 2011 Table 725.179Cable markings In the informational Note: .....and Class 3 cables are listed above Class 2 cables because Class 3 cables can substitute for Class 2 cables.

Thanks, we have established that but why can't NM - (what class is NM- or is it)- be used in place of class 3 as I mentioned above, Class 3 is current limiting cable- not sure what that means

 

[Speedskater]

I wasn't very clear.

Exception No. 2: Class 2 and Class 3 circuits shall be
permitted to be reclassified and installed as Class 1 circuits
if the Class 2 and Class 3 markings required in 725.124 are
eliminated and the entire circuit is installed using the wiring
methods and materials in accordance with Part II,
Class 1 circuits.
Informational Note: Class 2 and Class 3 circuits reclassified
and installed as Class 1 circuits are no longer Class 2
or Class 3 circuits, regardless of the continued connection
to a Class 2 or Class 3 power source.

(A) Sizes and Use. Conductors of sizes 18 AWG and 16
AWG shall be permitted to be used, provided they supply
loads that do not exceed the ampacities given in 402.5 and
are installed in a raceway, an approved enclosure, or a
listed cable. Conductors larger than 16 AWG shall not supply
loads greater than the ampacities given in 310.15. Flexible
cords shall comply with Article 400.

(B) Insulation. Insulation on conductors shall be rated for
600 volts. Conductors larger than 16 AWG shall comply
with Article 310.

So if we start with a Class 2 or 3 circuit and call it a Class 1, can we then use Art. 310 to select the wire?

 

[Dennis Alwon]

I

So if we start with a Class 2 or 3 circuit and call it a Class 1, can we then use Art. 310 to select the wire?

My understanding is if you start with a Chapter 3 wiring method then you must follow those rules.

 

[jumper]

My understanding is if you start with a Chapter 3 wiring method then you must follow those rules.

That is my understanding also, I can not say I agree with this rule for some cases-but that is the way I was taught.