barrier for 120v/ 24v

[bill@nkapc]

I believe a barrier is required for these different voltages in a single enclosure, i.e. switch box, but I can't find the art. # in the code book. Anyone know the art. number?

 

[iwire]

I believe a barrier is required for these different voltages in a single enclosure, i.e. switch box, but I can't find the art. # in the code book. Anyone know the art. number?

Most likely 725.55 but there are sometime other options than a barrier.

 

[Dennis Alwon]

I believe a barrier is required for these different voltages in a single enclosure, i.e. switch box, but I can't find the art. # in the code book. Anyone know the art. number?

There are times when 24 volts can occupy the same enclosure as 120v. One of the conditions is that the insulation on the 24 volt wire is rated as high as the insulation on the 120v conductor--

 

[don_resqcapt19]

Dennis,

There are times when 24 volts can occupy the same enclosure as 120v. One of the conditions is that the insulation on the 24 volt wire is rated as high as the insulation on the 120v conductor--

That statement is way too general. If the 24 volt system is an Article 725 Class 2 system, it can't be in the same raceway or enclosure as the 120 volt wiring, no matter what the insulation rating of the 24 volt conductors is, with some exceptions. You really need to look to 725.55 as Bob stated in his post.

 

[Dennis Alwon]

Dennis,

That statement is way too general.

Don I totally agree that's why I said there are times when this is allowed. I didn't know the OP's specific question or situation.

 

[infinity]

For some reason this a is a very common misconception. (24 volt circuit w/ 600 volt insulation = good to go). I hear this all of the time from electricians in the field. I wonder why so many forget about the separation requirements of Class 2 & 3 circuits.:-?

 

[Rockyd]

Sounds like a 725.55(D) issue.

 

[don_resqcapt19]

Trevor,

I hear this all of the time from electricians in the field. I wonder why so many forget about the separation requirements of Class 2 & 3 circuits.

Because they only read 300.3(C)(1) and not its FPN.
Don

 

[brantmacga]

you can buy a fiberglass divider to insert into most plastic multi-gang boxes to allow both voltages to occupy it. you can buy combo boxes also that have the divider already in place. low-voltage cables can be within the same enclosure only if they are functionally associated. for instance, w/ controls like the lutron grafik eye, you run PELV cable for remote scene controls back to the main controller, which connects to 120v.

 

[tom baker]

I wonder why so many forget about the separation requirements of Class 2 & 3 circuits.:-?

We all know 300.3(C)(1), read it and don't see the FPN at the end.
I would like to know when the FPN was added.
The term low voltage means nothing.
Note the 2 NEC articles on "low voltage" don't use low voltage in the title:
Art 720 and 725. I bet most of you have to look to see what Art 720 is. It covers DC wiring that was used in the 1920s' and 30's with DC generators and wind turbines before rural electrification.
A DC system that exceeds the limits of Art 725 Class II or III is then wired with a chapter 3 wiring method.

 

[hbiss]

I'm going to throw a monkey wrench into your interpretations. If you use a Class 1 wiring method for a Class 3 or a Class 2 circuit it is reclassified as a Class 1 circuit and can be run with other Class 1 conductors. I believe thats what 300(C)(1) means- "Conductors of circuits rated 600 volts nominal or less, ac circuits, and dc circuits shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable or raceway."

I say The FPN refers to Class 3 and Class 2 circuits wired with CL3 and CL2 listed wire per Art 725. Those conductors have an insulation rating of 300 and 150 volts respectively. It would also apply to communications cables such as coax, CAT cables, etc.

-Hal

 

[don_resqcapt19]

Hal,
I am going to "monkey it up even more". You are correct that Exception #2 to 725.52(A) permits you to reclassify a Class 2 or 3 circuit as a Class 1 circuit, however that does not mean that you can always install the reclassified circuit with power circuit conductors. The exception permits you to install the circuit as permitted in Part II of Article 725. Take a look at 725.26(B)(1). In general the reclassified circuit can only be installed with power circuit conductors if the two circuits are functionally associated.
Don

 

[hbiss]

I believe 725.26(A) would permit it. Once you reclassify you have a Class 1 circuit that must comply with Chapter 3- (725.25). The power supply circuits refered to again are Class 3 or 2 wiring methods.

I think the one thing we can all agree on is that 725 needs to be rewritten more clearly.

-Hal

 

[don_resqcapt19]

Hal,

I believe 725.26(A) would permit it. Once you reclassify you have a Class 1 circuit that must comply with Chapter 3- (725.25)

The use of the exception lets you install the Class 2 or 3 circuit as a Class 1 circuit and yes the circuit must be installed using a Chapter 3 wiring method, but it is still a Class 1 circuit and 725.26(B) tells you that in general Class 1 circuits cannot be installed with power circuits. 725.26(A) only applies to two or more Class 1 circuits within a common raceway or enclosure.
Don

 

[hbiss]

It does look like even though 300.3(C)(1) and the FPN permit it, no matter what you do 725.26(B)(1) apparently prohibits it even with a barrier unless the circuits are functionally associated.

-Hal