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How to Choose Low Voltage Wire for Audio and Security
Written by Don Schultz, Senior Technical Marketing Specialist, Fluke Networks Certified Copper/Fiber CCTT, BICSI TECH, INSTC, INSTF Certified
Speakers, doorbells, sensors, card readers, door strikes: they all run on low voltage wire, and the options (14/2, 18/4, 22/6) can be quite confusing. Sound and security low voltage wire is like the wild west of cable, as not all devices are the same and the rules for what gauge, conductor count, and wiring color code are different from device to device. Even maximum conductor lengths are installation specific. Best advice: Start with the device, not the wire. Let’s sort this out!
What Is Low Voltage Wire?
Low voltage wire is a very broad category that can include copper twisted pair Category (Ethernet) cable, coaxial cable, and sound and security cable. All are considered to be low voltage. In this blog we will be focusing on Class 2 and Class 3 power-limited circuits: audio, security, access control, cameras, and low-voltage lighting, for example.
These power limited CL2 and CL3 circuits are addressed with your typical copper conductors that look somewhat similar to higher voltage electrical wire located in your walls.
Sound and security wire may be solid or stranded copper. Solid copper allows for more distance due to less DC voltage resistance but offers less flexibility than stranded copper conductors.
Indoor Low Voltage Wire vs. Landscape Lighting Wire
Outdoor landscaping lighting wire is similar to indoor low voltage wire and comes in the same conductor gauges and counts, but has added UV protection and perhaps direct burial properties like gel filling. Low voltage landscape wiring may not be suitable for indoor use unless it is fire rated. Conversely, indoor low voltage wiring should not be used outdoors as it will quickly degrade in the elements.
Example Typical Devices Powered by Sound and Security Wire
Conductor Count: 2, 4, or 6?
Sound and security low voltage wire comes in multiple conductor counts to address different devices. Devices such as door contact sensors and speakers typically require only two conductors where card readers typically require more conductors for power and control.
The number of conductors required depends on the device itself.
Typical Conductor Count by Application Chart
| Conductors | Typical Use | Example Devices | Available Gauges |
|---|---|---|---|
| 2 | One circuit (+/-) | Speakers, door contacts, camera or lock power | 14, 16, 18, 22 |
| 4 | Power plus one signal pair, or two circuits | Powered motion sensors, keypads, speaker volume controls | 14, 16, 18, 22 |
| 6 | Power plus several data/control lines | Wiegand card readers (data, LED, beeper) | 22 only |
Please note that conductors are color-coded for polarity, but keep in mind that the above list is generalized, and each device may be wired differently from brand to brand. Always follow manufacturer instructions.
Wire Gauge: Matching Gauge to the Device
Wire gauge is measured in AWG, please see Demystifying AWG: Essential Guide to Understanding Wire Sizes for more.
Wire Gauge Ladder Chart
| Gauge | Max Continuous Amps (Pure Copper) | Typical Applications | trueCABLE Options |
|---|---|---|---|
| 22 AWG | 3A | Door contacts, motion sensors, keypads, card readers | 22/2, 22/4, 22/6 |
| 18 AWG | 5.6A | Lock and strike power, 12V/24V camera power, sirens, longer DC runs | 18/2, 18/4 |
| 16 AWG | 13A | Most home and in-wall speakers, higher-current DC | 16/2, 16/4 |
| 14 AWG | 15A | Long speaker runs, low-impedance speakers, high-current or long DC runs | 14/2, 14/4 |
Run Length Matters Too
Longer runs will likely need a thicker AWG conductor gauge. This is due to a phenomenon known as Insertion Loss which means additional length induces additional signal loss. This is normal, and just means you may have to upsize your conductors. Usually the manufacturer’s device will come with a table of gauge vs. length but you may need to refer to calculation charts and Internet resources to properly size your conductors.
There are on-line AWG length calculators available, but proceed with caution and always double check when you can.
Jacket Ratings: Where Low Voltage Wire Can Go
There will be printing on the cable jacket that indicates what the cable’s fire and electrical safety rating is. This rating defines where the cable may or may not be installed in residential (and especially commercial buildings). In the case of sound and security low voltage cabling, the electrical resistance fire safety rating is given as Class 2 or Class 3 (CL2 or CL3). The cable fire safety rating is normally given in conjunction with the Class rating with the addition of a letter like “R” or “P”. Therefore you will get an overall rating that looks like CL2R, CL3R, CL2P, CL3P, or something similar.
The Class rating is more aimed at helping to prevent a fire from starting at all from over-volting and accidental contact with adjacent high voltage AC circuits. The cable fire safety rating goes further and defines how the cable behaves in the event of a fire.
As a baseline, you want to start with a riser fire safety rating. This is often seen as CL2R or CL3R but may simply say “riser”. Riser rated cabling may be used anywhere inside a residential structure without limit. The same can be said for commercial structures unless you are dealing with a plenum area or a contract that says otherwise.
Residential structures are unlikely to need plenum rated cable meant for HVAC air handling spaces such as above drop ceilings or below raised floors.
Plenum fire rated sound and security cable will typically be printed with CL2P or CL3P.
Commercial structures are the most likely place you will need plenum fire rated cable. If your installation is commercial, always consult with the AHJ (Authority Having Jurisdiction) to confirm where plenum fire rated cable must be used instead of riser rated cable. It may well be that the entire commercial structure requires plenum rated cable due to insurance (not necessarily local Code) reasons. Don’t get this part wrong!
Unlisted sound and security cable won’t have a Listing number and was not tested by UL or ETL. Unlisted means no fire rating and is typically seen as OSP (Outside Plant) cable. Never use this kind of sound and security cable indoors!
For additional information, please see Facts About Ethernet Cable Jacket Ratings. Although that blog does not directly address sound and security cable, the general concepts still apply.
What is the Difference Between CL2 and CL3?
The difference between CL2 and CL3 (Class 2 vs Class 3) is defined under NEC (National Electrical Code) Article 725 and has to do with maximum voltage capacity.
- CL2 has a maximum voltage capacity of 150V
- CL3 has a maximum voltage capacity of 300V
CL3 is backwards compatible with, and may be substituted for, CL2 wiring unless a specific local Code Ordinance prohibits it. CL2 may not be substituted for situations that require CL3, however.
Keep in mind that CL2 vs CL3 is all about electrical fire safety and electrical insulation limits. There is no difference in audio quality, for example, between CL2 and CL3 of the same gauge and build type.
Why Getting It Right Matters
Quite simply, get this wrong and you put lives and property at risk. This is not something you can get wrong. Getting it wrong means delayed projects, rework, potential fines, civil litigation, and even criminal exposure.
- Undersized wire leads to voltage drop, which shows up as locks that won’t release, dim or flickering lights, distorted audio, and devices that reset
- If you used the wrong wire you may have to remove it and replace it
- In the event of a catastrophic event like a fire, the contractor that put the cable in is the first stop for liability and you will be on the hook if you got it wrong
This is why trueCABLE does not recommend Copper Clad Aluminum, aka CCA. CCA has significantly higher electrical resistance, resulting in CCA wire behaving like a thinner gauge of pure copper wire. This can lead to conductor sizing and length mistakes that may damage property or even cause a fire in extreme edge case circumstances.
Quite simply, CCA can’t safely carry the same current as the equivalent pure copper wire and it cannot go as far.
Take a look at Check Your Specs, CCA Is Different From Solid Copper.
Where to Find Your Device’s Cable Requirements
Sound and Security Cable Selection Tip Table
| Source | What to Look For | Tip |
|---|---|---|
| Device packaging | Recommended AWG, conductor count, max run | Often printed near the wiring diagram |
| Manual or spec sheet | AWG, current draw (amps), voltage | Current draw plus run length decides gauge |
| Manufacturer website | Install guides, wiring diagrams, FAQs | Search the exact model number |
| Installer or manufacturer support | Confirmation for long or unusual runs | When unsure, go one gauge thicker |
Frequently Asked Questions
What wire should I use for low voltage?
trueCABLE recommends pure oxygen free (OFC) copper conductors, and selection of the correct gauge and conductor count is entirely device/installation dependent.
Can I use 14/2 wire for low voltage?
Yes! In fact, some applications will require it. That said, don’t mistake 14/2 sound and security wire for 14/2 NM-B house wire! That kind of wire is meant for in-wall high voltage AC circuits.
Can you run low voltage wire without conduit?
Generally, yes. That said, you need to check with your AHJ (Authority Having Jurisdiction) regarding any local Code Ordinance requirements.
Is low voltage wire the same as landscape lighting wire?
In most ways yes. In the most important ways: No. Landscaping lighting wire might have the same conductor gauge and counts you wish to use indoors but the landscape wire may not be appropriately fire rated for indoor use. Conversely, don’t use indoor-only low voltage cable outdoors since it is not built to withstand outdoor elements.
What does CL3R / CMR riser rated mean, and where can it legally go?
CL3 is the Class rating of the wire. CL3 means the cable is electrically designed to withstand 300V. This rating is meant to help an installer avoid over-volting a wire that could not otherwise handle it and thus avoid a fire in the first place. The “R” means riser rated and defines where the cable can be installed in any particular structure. The riser rating defines how the cable behaves if an actual fire happens. Riser rating cable of any type indicates it may be used between floors and in-wall, but not plenum (HVAC) areas of a commercial building.
Why does pure copper matter compared to CCA?
Pure copper conductors have much lower resistance to electricity. CCA tends to easily break during installation, behave like thinner gauge pure copper wire, and won’t perform as well over time due to oxidation. trueCABLE recommends pure copper sound and security wire and avoiding CCA.
What happens if I choose wrong?
In the best case scenario your installation may not work as you desire. In extreme cases choosing wrong has legal implications you would rather not deal with. In short, if you do choose wrong you are best off replacing the improper wire.
Conclusion
So there you have it! Selecting sound and security low voltage cable is not as straightforward as selecting Ethernet. With sound and security low voltage installations you must consider your device needs first, then conductor count, then gauge, and then rating, then confirm with the manufacturer. You may be in for some research but that is all part of the fun and learning process.
HAPPY NETWORKING!!
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