Low voltage wiring bundling conventions

[paw500]

I am in the process of wiring my Elk M1G as retrofit in my home and have some questions regarding the general routing of low-voltage (LV) conductors and cables.

I understand that LV wiring should be kept away ( >1 feet) from high voltage 120/240V AC lines when running parallel, and must cross perpendicularly.

However how do you treat the bundling of different types of LV cables? I thought there would be no problems, until I read in some footnote in the M1G installation manual that "power-limited" conductors can't be run next to "non-power-limited" conductors (i.e. the battery leads going into the panel board) - there needs to be a minimum 1/4" separation or airspace between LV-limited and LV-non limited wires, despite these all being ~12VDC in this case. (see page 68, L520 Rev. J 10/28/10 manual)

Now then, do I have to be concerned with separating low current and high current LV wires? Data-comm cables and voltage only cables? I foresee having to run (as a bundle, in wire duct, or in conduit) any or all of the following types of LV cables at some points in my installation:
2c/22 sensors,
4c/22 sensors+power,
4c/18 firewire life-safety detectors,
4c/18 or Cat6 databus components,
Cat6 ethernet LAN,
Cat6 POT,
2c/16 (or greater) speakers/sirens/strobe,
2c/14 (or greater) remote VAux 12VDC power

Here are a couple of scenarios I'm considering:

1. I plan to mount a remote can in a bedroom area linen closet in which there will be a zone input expander and output expander, along with aux 12VDC power. (Since there is no AC receptacle in this closet I can not put a local power supply in this can.) Point run to this can will be smoke, heat, CO detectors as well as a few burglary sensors and a keypad. Outputs may include a strobe or speaker. Between the main panel in the basement and this remote can, I will run a 4c/18 cable for databus, and 2 sets of 2c/14 for SAux (switched and reversible for the smokes) and for unswitched VAux. Any problems bundling these 3 cables for the run between the cans? Are the SAux and VAux conductors considered "power-limited" if the power is sourced from a P212S supervised power supply (which has its own battery back-up)?

2. In a hall closet I will install a wire duct to run LV cables between the basement, main floor, and attic. In this closet I will also mount a wireless receiver for interfacing with some wireless sensors. There will be many wires bundled in this duct for sensors, databus components, aux 12VDC power, speakers, and a siren mounted in the attic vent. I may also route Cat6 for GigE LAN and RG6 for video via this wire duct. Any problems bundling all these different types of cables within the same vertical duct?

My concerns for problems include interference, data transmission reliability, signal quality, besides electrical safety.
Thanks for your insight.

 

[Del91574]

There really is no distinction between the cables you're referencing as far as LV wiring conventions go. The distance you are citing is more of a guideline and sounds more like an audio sort of specification from a place like Crutchfield, nothing that is contained within the NEC. Installing home audio has some best practices for speaker cable runs that sound like that, but really no other systems I know of.

The NEC cites separation of cables and conductors as an exception in concealed places, and by retrofit, that's what you're doing.

The Elk manual cites the separation for battery leads and batteries themselves because they are unfused, and while they are low voltage, there exists the potential for high amperage should you short the battery terminals or a damaged battery lead with a conductor or to the enclosure itself.

When doing a full LV installation on a house, including structured wiring, MAC-6 for video, Category cables and LV for audio, alarm, control, etc. depending on the runs, I try to separate out the structured and category cabling and bundle like systems together, but that's more for neatness than anything else, not a code requirement.

1. While it is often overlooked by AHJ's and people installing panels in closets, the clearances and safe working distances should be observed wherever possible, that's just my opinion. I also believe, unless there is an extreme wiring distance or draw, that using 4/18 for your bus is overkill and unnecessary, as is the 14awg for the smokes, unless the draw or install demands such, not to mention the cable is going to be more difficult to work with. Same thing goes with your speaker/siren/strobe wiring. A pair of 18/2 has an ampacity of 8A for a 500' length, where most strobes draw >200mA. The only thing I prefer to do personally with the Elk's I put in is homerun the speakers and then wire appropriately for the correct impedance because I'm usually using 32 ohm interior speakers, but the same applies even if you used 4 or 8 ohm speakers.

2. The only thing that is worth note here is the pulls to maintain integrity of the Category cabling. Pull tension is 25# on a Cat. cable, and if you're bundling that much in a single innerduct, then I'd be concerned personally. I can't say about your personal construction details, but as long as the wiring is installed correctly, no separation requirements based on LV cable type is necessary.

I think most people are misguided when it comes to LV wiring because of the bigger-is-better theory and Monster Cable sorts of things.

 

[paw500]

Thanks for the clarifications.

So the term "power-limited" means the wire or circuit is fused, and has nothing to do with the amount of the amperage running through it? Thus it is ok to run a sensor circuit with a tiny draw of 25ma, or a keypad databus drawing 160ma, bundled with siren wiring that may have a 1000ma draw, and there wouldn't be any kind of interference between and among the conductors? I have also read specifications for devices (such as the System Sensor i3 2-wire smokes) where the current draw is given but footnoted that such current draw must be "limited by the panel." Does this notation mean the panel may regulate current and provide less than, but the device may draw up to, the specified current; or does it mean the panel must be fused at that specified current (i.e. 130ma at max alarm for the 2WTR-B or 2WTA-B )? (On a tangent here: In terms of energy consumption/battery loading, why would anyone choose the SS i3 2-wire smokes with higher specified max alarm current draw rather than their 4-wire smokes with less respective current draw?)

Regarding the use of 4c/18 for the databus in my first scenario above, I have read that if the smokes are all wired with 4c/18 firewire, then everything upstream back to the main panel must be wired with the same type and sized cable.

With regard to residential installations, are there any instances where FPLP (plenum rated) cables are required? I have forced-air HVAC, yet I cannot think of any reason why anyone would run wiring INSIDE the air ducts or compromise the ducting.

Under what circumstances would LV "shielded" cables be used (it seems they make a shielded and unshielded version of every type of cable)? Also does any remote can housing only LV circuits and components need to be grounded?

 

[tmbrown97]

Most of my professional wiring experience comes from the commercial settings - but in those environments it's not uncommon at all for me to combine audio/video/lan in smaller conduits (to a conference table via in-ground conduit) - or in larger between-building runs, fiber, alarm, coax, CatX, 100-pair Cat3, etc... really I've never had issues combining things as long as you keep high voltage separate. When running audio cabling I prefer shielded because it helps isolate noise, but kinda as DEL hinted to above - don't fall victim to the monter cable philosophies (over-complicating a solution to a problem that doesn't exist to begin with).

The only issues I've had is when combining high-voltage with low voltage wiring. In the case of audio/video, I've seen the noise degrade the signal or introduce noise to an unusable state; and I once saw a set of Cat5e runs redone 3 times - each time it passed continuity repeatedly but wouldn't carry data - that was because the electrician (who didn't belong running low voltage) ran Cat5e and High Voltage through the same pass-through... once they were separated out, the cables passed certification and functioned fine.

For long analog (non amplified or low-level) audio/video runs you can be more succeptible to noise introduction... just depends on the environment. If you're running your RCA connections via Coax, it's shielded and generally fine. You're correct - plenum shouldn't be required in a typical residential setting unless for some reason you're entering the air handling space. In commercial settings it's very common for the space above the ceiling tiles to be considered air handling space therefore plenum comes up pretty often in commercial settings; and lots of low voltage installers who don't properly understand the difference just default to plenum to "be safe".

 

[Sandpiper]

"Power limited", in terms of the NEC, is intentional limiting of voltage and current in conductors to conditions as specified by NEC Article 725. There are 3 levels of "limited" defined there, but for alarm systems, most fall under Class 2. Class 2 alarm circuits are limited by the supply transformer a nominal 12VAC and 40VA. By "limiting" the circuits, the rules for wiring under Article 725 then apply. When Article 725 applies, then the rules for almost all the rest of the code can be ignored. However, one rule that does apply is that the "limited" conductors must be separated from the "non-limited" conductors. There are specific rules in Article 725 addressing this. One of them, 725.136(D), applies when "limited" conductors are in the same enclosure as "non-limited". There a separation of 1/4" must be maintained.

Alarm system wiring is "limited" by the power supply transformer, except for the battery leads. The battery leads can supply more power than what the "limits" allow. So that is why the caution is placed in the manual about separation from other wiring. And no, paragraph 725.136(A) prohibits placing "limited" conductors in the same conduit or raceway as with "non-limited" conductors.

 

[Digger]

Just a few things to note in this thread so that someone looking at it in the future is not confused:

Power Limitation can not be obtained using fuses. The supply must be inherently limited or use a PTC for protection.

Seperation of Power Limited and Non Power Limited conductors by 1/4 inch is one method of complying with the NEC. Some manufacturers have opted to provide a barrier instead (such as UL Recognized Tubing that is appropiatly rated for the application). I have personally had many products UL Listed doing that to make it easier on the installer to comply with the NEC. I think some mfgs are using UL Recognized double insulated wire on their battery leads in higher end equipment but I have not tried that approach yet but believe it meets the UL and NEC requirements.

Outputs of an alarm system (zones, bell circuits, databuss etc) are Power Limited by a PTC or in a few cases a solid state circuit and are considered Power Limited that way and NOT by the transformer. A Class 2 transformer does not necessarily mean it is Power Limited as defined by the NEC (Tables 11 and 11A if I remember correctly). Many Class 2 transformers have an internal fuse and are not inherently limited or protected by a PTC so they can not be considered Power Limited. Also the battery is a secondary source of power and must be limited by a PTC or a solid state circuit (often seen on NAC circuits in a Commercial Fire Panel).

 

[Sandpiper]

Just a few things to note in this thread so that someone looking at it in the future is not confused:

Power Limitation can not be obtained using fuses. The supply must be inherently limited or use a PTC for protection.

Seperation of Power Limited and Non Power Limited conductors by 1/4 inch is one method of complying with the NEC. Some manufacturers have opted to provide a barrier instead (such as UL Recognized Tubing that is appropiatly rated for the application). I have personally had many products UL Listed doing that to make it easier on the installer to comply with the NEC. I think some mfgs are using UL Recognized double insulated wire on their battery leads in higher end equipment but I have not tried that approach yet but believe it meets the UL and NEC requirements.

Outputs of an alarm system (zones, bell circuits, databuss etc) are Power Limited by a PTC or in a few cases a solid state circuit and are considered Power Limited that way and NOT by the transformer. A Class 2 transformer does not necessarily mean it is Power Limited as defined by the NEC (Tables 11 and 11A if I remember correctly). Many Class 2 transformers have an internal fuse and are not inherently limited or protected by a PTC so they can not be considered Power Limited. Also the battery is a secondary source of power and must be limited by a PTC or a solid state circuit (often seen on NAC circuits in a Commercial Fire Panel).

I'm afraid you are mistaken. The very meaning of a "Class 2" transformer is that it meets the requirements of NEC Tables 11A or 11B for the power limitation. And when, applied in the correct manner, a fuse can indeed provide the "limitation for a Class 2 or 3 circuit. Tables 11A and 11B both have columns which specify conditions for "Not Inherently Limited Power Source (Overcurrent Protection Required). The code does not specifically state what type of "overcurrent protection" is required in this case, but several devices can be used to limit current, including a simple resistor, a fuse, or PTC.

 

[Digger]

I'm afraid you are mistaken. The very meaning of a "Class 2" transformer is that it meets the requirements of NEC Tables 11A or 11B for the power limitation. And when, applied in the correct manner, a fuse can indeed provide the "limitation for a Class 2 or 3 circuit. Tables 11A and 11B both have columns which specify conditions for "Not Inherently Limited Power Source (Overcurrent Protection Required). The code does not specifically state what type of "overcurrent protection" is required in this case, but several devices can be used to limit current, including a simple resistor, a fuse, or PTC.

A Class 2 circuit and Power Limited Circuit are NOT the same thing (yes similar). You can not have a circuit be power limited by a fuse. To meet Power Limited you must be Inherently Limited or protected by a PTC or solid state circuit. Additionally a fuse (or PTC or inherently limited transformer etc) can be used to meet Class 2 but NOT a fuse to meet Power Limited requirements.

A fuse has 60 seconds to react to meet Class 2 but Power Limited must be met in 5 seconds with a PTC or inherent limitation. Even if a fuse was to open in 5 seconds or less it would not be considered a Power Limited Circuit.

Additionally the NFPA requires a PTC or solid state circuit to operate within 5 seconds at 0 to 49C. That is why you rarely see PTC in higher power circuits (over a couple of amp etc) of an alarm panel such as a NAC circuit on a FACP. Now most in the industry use current sensing circuits and shut off a FET Transistor to meet the requirements over the temperature range.

You are confusing the means to achieve Class 2 with Power Limited requirements.

 

[wuench]

So that's all a lot of details and jargon that's frankly over my head. But just to simplify based on other discussions in other threads. I think it was stated the wires to the battery need to be separated and not in the same conduit from the wires to zones,cat5,coax, etc. Or alternatively, I think it was said you can just put a fuse on the battery to limit it.

The reason being, basically if it's not protected by a fuse or circuit breaker, if the wires shorted for some reason the battery or other unlimited/unprotected circuit could potentially route a lot of power onto other wires and cause an electrocution or fire hazard.

Is that a good summary?

 

[tmbrown97]

Not to hijack the original thread, but this is good information... I My installation includes a 50" CV Can with the plexi door, and a 20" OnQ can below; my plan was to keep all the power (including the battery) in the bottom can and the electronics above. Of course this would mean extending the battery leads - I had figured I'd be safe using a fuse but according to this, that's not the case... so Digger - how would you then protect the circuit so it's legal and doesn't require the isolation?

 

[Digger]

So that's all a lot of details and jargon that's frankly over my head. But just to simplify based on other discussions in other threads. I think it was stated the wires to the battery need to be separated and not in the same conduit from the wires to zones,cat5,coax, etc. Or alternatively, I think it was said you can just put a fuse on the battery to limit it.

The reason being, basically if it's not protected by a fuse or circuit breaker, if the wires shorted for some reason the battery or other unlimited/unprotected circuit could potentially route a lot of power onto other wires and cause an electrocution or fire hazard.

Is that a good summary?

Electrocution no. Fire hazard yes. A 7 or 8 Ah battery can have a short circuit current of nearly 100 A (not for very long) but enough to produce a lot of heat.

 

[Digger]

Not to hijack the original thread, but this is good information... I My installation includes a 50" CV Can with the plexi door, and a 20" OnQ can below; my plan was to keep all the power (including the battery) in the bottom can and the electronics above. Of course this would mean extending the battery leads - I had figured I'd be safe using a fuse but according to this, that's not the case... so Digger - how would you then protect the circuit so it's legal and doesn't require the isolation?

I sleeved my battery leads in tubing. I also used a fuse as well. Technically the fuse alone does not meet the code but the tubing is a barrier instead of the 1/4" spacing. The fuse though is nice to have in addition to the tubing.

 

[Del91574]

Not to hijack the original thread, but this is good information... I My installation includes a 50" CV Can with the plexi door, and a 20" OnQ can below; my plan was to keep all the power (including the battery) in the bottom can and the electronics above. Of course this would mean extending the battery leads - I had figured I'd be safe using a fuse but according to this, that's not the case... so Digger - how would you then protect the circuit so it's legal and doesn't require the isolation?

A separate battery can is fine, the best way, if you're old working the enclosure(s) would be to fish the new battery leads in the bay next to the cans and bring them in a side knockout nearest where the batteries are and where the nearest knockout to the panel you can get to the battery leads. The absolute best would be in a separate conduit outside of both enclosures, connected with fittings, etc. to an appropriate knockout. The legality of it would be to ask the manufacturer if it is legal for you to extend the leads, of course.

 

[Digger]

You have to be careful of adding a voltage drop if you extend leads to much. Best to move up a gauge or two in wire if you can. But it has to fit terminal block etc.

I went to 14 awg if I remember correctly because I have 26 Ah batteries on my system and they obviously dont fit in the can's.

 

[Digger]

A separate battery can is fine, the best way, if you're old working the enclosure(s) would be to fish the new battery leads in the bay next to the cans and bring them in a side knockout nearest where the batteries are and where the nearest knockout to the panel you can get to the battery leads. The absolute best would be in a separate conduit outside of both enclosures, connected with fittings, etc. to an appropriate knockout. The legality of it would be to ask the manufacturer if it is legal for you to extend the leads, of course.

When you say in the bay do you mean in the wall? A non power limited wire in the wall like that? In conduit (rigid or flexible I think both would meet code) yes but unprotected would not meet code.

A non power limited circuit would require Class 1 wiring methods (conduit etc).

I used tubing in the enclosure and then outside the enclosure I put the wire with the tubing in smurf tubing for mechanical protection up to the battery carrier (way overkill). I placed a fuse within a couple inches of the positive of the battery and that is still inside the battery carrier. My battery leads are not Power Limited but they are protected by the tubing (and an additional smurf tubing outside the enclosure).

Again what I did is overkill but 26 Ah batteries have a lot of short circuit current.