Power Limited Circuits - FAQ

[Sandpiper]

A new Library item was uploaded today, entitled "Power Limited Circuits - FAQ". Power Limited Circuits is what we use when wiring burglar and fire alarm systems. It is found in the "Downloads/Library/Wiring Diagrams section. Here is a link.

I would appreciate constructive comments to help improve the document. Please let me know if you find any problems or have additional questions.

Sandpiper

 

[Neurorad]

Thanks so much, Sandpiper. Great job.

Can you include a copy of the NEC with that download?

 

[Del91574]

A copy of the chart with substitutes for the cable types would probably benefit most. THe document also doesn't address article 800, which is also applicable in this case, but I don't know if you'd put that in as well.

There are rule bending parts that the topic doesn't necessarily address, but I don't think this would be an appropriate venue, such as running LV circuits in the same conduit as HV circuits (it is allowed, provided some key points are met) and a few other items of interest.

Good post overall.

 

[Photon]

Nice compilation, Sandpiper.

Regarding para 11.6:

11.6. Class 2, Class 3, or PLFA circuit conductors may not be installed in the same
cable or raceway with an audio systems circuit, even if the audio system circuit is
classified as Class 2 or Class 3 PLC. [725.139(F), 760.139(D)]​

Does this apply to audio from the Elk M1? It appears I am in violation by having audio to Elk speakers in the same conduit as Class 2 zone input cables.

 

[paw500]

Thanks for putting this together.

A couple of questions:

In your paragraph number 6, you wrote: "Class 1 circuits allow significantly more power to the circuit than Class 1, Class 2, or Power-Limited Fire Alarm circuits do." What do you mean when you compare the two 'Class 1' circuits here?

In paragraph 11.6 "Class 2, Class 3, or PLFA circuit conductors may not be installed in the same cable or raceway with an audio systems circuit, even if the audio system circuit is classified as Class 2 or Class 3 PLC." Does this mean wiring for sirens, bells, piezo screamers, speakers, etc., or mics for 2-way listen-in must be separated from other burglar/fire alarm Class 2 circuits? How about audio signals transmitted digitally, such as via TCP/IP?

 

[Sandpiper]

A copy of the chart with substitutes for the cable types would probably benefit most. THe document also doesn't address article 800, which is also applicable in this case, but I don't know if you'd put that in as well.

There are rule bending parts that the topic doesn't necessarily address, but I don't think this would be an appropriate venue, such as running LV circuits in the same conduit as HV circuits (it is allowed, provided some key points are met) and a few other items of interest.

Good post overall.

The substitution chart for cable types is readily available on the internet. I didn't think it would be worthwhile re-creating it. If you understand the words, the chart is not necessary. Article 800 (communication circuits) is mentioned several times in the document, but that is not the main focus.

I don't agree that LV circuits can be run with HV circuits in the same conduit. If this is permissible, I'd really like to hear about where in the code this is allowed.

 

[Sandpiper]

Nice compilation, Sandpiper.

Regarding para 11.6:

11.6. Class 2, Class 3, or PLFA circuit conductors may not be installed in the same
cable or raceway with an audio systems circuit, even if the audio system circuit is
classified as Class 2 or Class 3 PLC. [725.139(F), 760.139(D)]​

Does this apply to audio from the Elk M1? It appears I am in violation by having audio to Elk speakers in the same conduit as Class 2 zone input cables.

I thought of that, but did not dig deep enough on this point. I really doubt of this is the intent of the code. But the code states " audio system circuits described in 640.9[C] and installed using Class 2 or Class 3 wiring methods ....... shall not be permitted to be installed in the same cable or raceway with Class 2 or Class 3 conductors".

Then 640.9[C] states "Amplifiers with outputs carrying audio program signals shall be permitted to employ Class 1, Class 2, or Class 3 wiring....." Does the M1 speaker circuit qualify as an "amplifier with outputs carrying program signals"? I dont think this is the intent. But I will try to find out.

 

[Sandpiper]

Thanks for putting this together.

A couple of questions:

In your paragraph number 6, you wrote: "Class 1 circuits allow significantly more power to the circuit than Class 1, Class 2, or Power-Limited Fire Alarm circuits do." What do you mean when you compare the two 'Class 1' circuits here?

In paragraph 11.6 "Class 2, Class 3, or PLFA circuit conductors may not be installed in the same cable or raceway with an audio systems circuit, even if the audio system circuit is classified as Class 2 or Class 3 PLC." Does this mean wiring for sirens, bells, piezo screamers, speakers, etc., or mics for 2-way listen-in must be separated from other burglar/fire alarm Class 2 circuits? How about audio signals transmitted digitally, such as via TCP/IP?

For paragraph 6, that is an OOPS. Class 1 allows more power than Class 2, Class 3 and Power-limited Fire alarm circuits. I will correct. thanks for the catch!!!

For 11.6 this is the same question photon asked, so I will dig into this. But I don't think this is the intent. I agree the document would be more helpful if this was clarified. If the code was taken literally on this point, there would be code violations on every alarm system install.

 

[Sandpiper]

I found out about the audio signals issue. In section 640.1 of the NEC, under FPN No.2, it states, "Fire and Burglary alarm signaling devices are specifically not encompassed by this article."

So that means that audio from alarm systems are excluded from the requirement in 725.139(F) about mixing audio and Class 2 or Class 3 circuits in the same conduit. (760.139(D) for fire alarms).

Thanks for the catch photon and sixspeed. I will make the clarifications.

 

[Del91574]

The substitution chart for cable types is readily available on the internet. I didn't think it would be worthwhile re-creating it. If you understand the words, the chart is not necessary. Article 800 (communication circuits) is mentioned several times in the document, but that is not the main focus.

I don't agree that LV circuits can be run with HV circuits in the same conduit. If this is permissible, I'd really like to hear about where in the code this is allowed.

800 is where the runs to multiple buildings start to come in on top of the other wiring methods, so it is a valid citation if people are doing multi-area installs.

It's allowable if the the wiring methods and ratings are the same as the HV cabling. If you've got 1000V THHN in a conduit, then the LV circuits would need to carry the same voltage rating on their insulation as well. This example came up multiple times within my state's continuing ed for electricians as well as during the apprenticeship and license tests. Is it logical, no, but some situations may come up where you're limited to a conduit already in place. Have I seen 1000V rated coax or other cables commonly, no, but they do exist.

I would have to get my copy of the NEC to cite the specific articles, but it's all there.

The only thing I would ask for clarification on is which version of the NEC are you citing?

 

[Sandpiper]

800 is where the runs to multiple buildings start to come in on top of the other wiring methods, so it is a valid citation if people are doing multi-area installs.

It's allowable if the the wiring methods and ratings are the same as the HV cabling. If you've got 1000V THHN in a conduit, then the LV circuits would need to carry the same voltage rating on their insulation as well. This example came up multiple times within my state's continuing ed for electricians as well as during the apprenticeship and license tests. Is it logical, no, but some situations may come up where you're limited to a conduit already in place. Have I seen 1000V rated coax or other cables commonly, no, but they do exist.

I would have to get my copy of the NEC to cite the specific articles, but it's all there.

The only thing I would ask for clarification on is which version of the NEC are you citing?

Ok. I understand your point now, and I agree. Take a look at paragraph 20. It talks about this very point. You can do this, but then the LV circuit may still be LV, but it is not considered Power-Limited and is not wired using Article 725 anymore. Other Articles will then apply.

If you look at preamble paragraph, it mentions that the 2008 code is being quoted.

Again, this document is intended for residential applications......Most Cocooners just want to know how to wire their house properly...to code. For purposes of this discussion, I'd rather stay away from commercial and industrial installation practices, as this just confuses the issue.

 

[mikejrc]

Ok. I understand your point now, and I agree. Take a look at paragraph 20. It talks about this very point. You can do this, but then the LV circuit may still be LV, but it is not considered Power-Limited and is not wired using Article 725 anymore. Other Articles will then apply.

If you look at preamble paragraph, it mentions that the 2008 code is being quoted.

Again, this document is intended for residential applications......Most Cocooners just want to know how to wire their house properly...to code. For purposes of this discussion, I'd rather stay away from commercial and industrial installation practices, as this just confuses the issue.

I agree with you Sandpiper. Under certain conditions the code allows you to run LV and HV wires in the same conduit, but it is not common practice out there, at least in my line of work (commercial, industrial). We usually run separate conduits and I would do the same in residential just for safety.

Thanks for the document, well written.

 

[Sandpiper]

The FAQ has been updated to correct some typos, and to add some clarifications. Thanks for your interest and help in improving the document.