IRC 2024 Low-Voltage Wiring: Data, Audio, and Security Cable Installation Rules

Quick Answer

Under IRC 2024 Section E4301, low-voltage wiring for data networks, audio systems, security systems, doorbells, and similar applications is classified as Class 2 or Class 3 wiring. These cables must be kept physically separated from 120-volt and 240-volt power conductors — they cannot share the same raceways, boxes, or openings without a listed separator. Cable ratings matter: plenum-rated cable is required in plenum air-handling spaces, and riser-rated cable is required in vertical shafts.

Under IRC 2024, fire-stopping at all penetrations through fire-rated assemblies is required the same as for power wiring. Cables must be supported and secured and cannot be left loosely draped or stapled with improper fasteners.

What IRC 2024 Actually Requires

IRC 2024 Section E4301 adopts by reference the NEC provisions for Class 2 and Class 3 low-voltage wiring systems, which govern the installation of data cables, audio and video cables, security system cables, fire alarm wiring, doorbell and intercom wiring, and similar low-energy circuits that operate at voltages and power levels below the thresholds for standard branch circuit wiring.

The defining characteristic of Class 2 and Class 3 wiring is their power limitation. Class 2 circuits are limited to 100 VA (volt-amperes) at less than 30 volts, or to lower power levels at higher voltages. Class 3 circuits allow up to 100 VA at up to 150 volts. These power limitations reduce but do not eliminate the shock and fire hazard, which is why specific installation rules still apply. The low power levels do allow more flexible installation methods than full-power branch circuits, including stapling with appropriate fasteners rather than conduit-protected runs in many locations, and smaller cable diameters that can share wall cavities with power wiring as long as physical separation is maintained.

Physical separation from power wiring is mandatory. Low-voltage cables shall not occupy the same raceway, conduit, or wireway as Class 1 (power) wiring unless the raceways are listed for mixed use and the cable types are specifically permitted to share that raceway. In practice, this means that data cables, speaker wire, and security cables run in wall cavities alongside NM-B power cables must maintain physical separation — they cannot be bundled with power cables or run through the same drilled holes without a listed separator. In junction boxes, low-voltage conductors shall not enter the same box opening as power conductors; they may enter the same box only through a separate opening on a different face of the enclosure, or they must use a listed barrier or separator inside the box to maintain separation between the low-voltage and power conductors.

Cable jacket ratings determine where each cable type may be installed. CMR (communications riser) rated cable is the minimum requirement for cables installed in vertical shafts or risers that penetrate floor assemblies and create a vertical path that could allow fire and smoke to travel between floors. CMP (communications plenum) rated cable is required wherever cables are installed in air-handling spaces — the spaces above suspended ceilings that are used as return-air plenums in HVAC systems, and in spaces under raised floors used for supply air distribution. Plenum-rated cable uses a jacket material that produces less smoke and toxic gases in a fire than standard PVC-jacketed cable, reducing the risk of smoke spreading through the HVAC system to other parts of the building.

Why This Rule Exists

The separation requirement between low-voltage and power wiring addresses two distinct hazards. The first is cross-talk induction — the electromagnetic field generated by a 120-volt power conductor can induce noise and interference in adjacent data or audio cables, degrading signal quality. While this is a performance issue rather than a safety issue, it reinforces the importance of physical separation. The second hazard is more serious: if a fault in a power conductor causes voltage to be transferred to a low-voltage cable (through insulation breakdown, chafing, or direct contact), the equipment connected to that low-voltage cable is suddenly exposed to mains voltage, creating a shock hazard at data ports, speaker terminals, and security system touch panels that users would not expect to be energized.

The plenum cable requirement addresses the specific hazard of HVAC systems distributing smoke and combustion products in a fire. In a return-air plenum ceiling, all the air in the building passes through that space to return to the HVAC system. If standard PVC-jacketed cable burns in that space, the PVC releases dense black smoke and chlorine-containing gases that the HVAC system circulates throughout the building, incapacitating occupants in rooms far from the fire. Plenum-rated cable reduces this hazard significantly with a more fire-resistant jacket material.

Fire-stopping requirements for low-voltage cable penetrations close a common vulnerability: small-diameter data and communication cables that penetrate fire-rated floor-ceiling assemblies or fire walls create pathways for fire and smoke to move between compartments. Because low-voltage cables are numerous (a modern home might have dozens of data, security, and audio cable runs), each penetration through a rated assembly must be fire-stopped with listed materials the same as for power cable penetrations.

What the Inspector Checks at Rough and Final

At rough-in inspection, the inspector checks whether low-voltage cables are separated from power conductors at all shared wall cavities and boxes. A data cable bundled tightly against NM-B power cable through the same drilled hole, or entering the same box opening as power conductors, will be flagged. The inspector also checks cable jacket ratings at visible locations — if cable is run through a space above a suspended ceiling that serves as a return-air plenum and the cable jacket is not marked CMP, the installation will fail.

The inspector looks for fire-stopping at penetrations through fire-rated assemblies, including top plates in fire-rated wall assemblies, penetrations through floor-ceiling assemblies, and penetrations through garage-to-living-space separation walls. Low-voltage cables that penetrate these assemblies and are not fire-stopped are a fail item, as they compromise the fire resistance of the assembly. Fire-stop materials must be listed for the specific cable type and penetration size.

At final inspection, the inspector checks that all low-voltage cable runs are properly supported without excessive sag, that cables are not pinched at corners or door frames, and that any exposed low-voltage panels or boxes are properly covered with listed enclosures. The inspector also verifies that the home’s low-voltage wiring does not create tripping hazards or present unprotected cables in locations where they could be stepped on or damaged.

What Contractors Need to Know

In new residential construction, the separation between low-voltage and power wiring is most efficiently achieved during rough-in by planning separate stud-bay routes for data and power runs and using separate drilled holes for low-voltage cables versus power cables. A common practice is to drill low-voltage holes 6 to 12 inches above or below power cable holes so that cables in adjacent holes are not co-located and cannot contact each other. Where shared routing is unavoidable, use listed barrier fittings at holes where both cable types must pass.

For structured media centers (the central distribution point for a home’s data, cable TV, and telephone wiring), select listed enclosures that include listed barriers between the power section and the low-voltage section. These are specifically designed for this purpose and satisfy the separation requirement in a single box installation.

When specifying cable types for new construction, default to CMP (plenum) rated cable throughout the home rather than mixing CMR riser cable in some locations and plenum cable in others. While plenum cable is more expensive, using a single cable type eliminates specification errors and ensures that any future HVAC redesign that converts a ceiling cavity to a plenum space does not create a code violation with previously installed riser-rated cable. In homes with traditional ductwork (no plenum ceilings), CMR riser cable is compliant in most locations except vertical shaft penetrations.

What Homeowners Get Wrong

The most common homeowner error with low-voltage wiring is running data cables through the same box opening as power conductors — for example, routing a network cable through the wall to a living room outlet box and feeding it out the same opening as the power conductors. This violates the separation requirement. Network cables and power cables may share a wall plate (there are combination plates with both a power outlet and a keystone data jack), but the cables must enter the box through separate openings on separate knockouts, or through a listed box with an internal separator.

A second frequent mistake is using generic string or zip ties to bundle and support low-voltage cables, which is acceptable, versus using staples intended for power cable. Standard NM cable staples are too large for data cables and can crush and deform the cable jacket, which for data cables (especially Cat 6 and Cat 6A) can affect the cable’s electrical performance even without visible damage. Specialty data cable staples sized for the cable diameter should be used, and they should be installed snugly but not tightly. Avoid sharp bends at corners — Cat 6 data cable has a minimum bend radius of approximately 1 inch that, if violated, reduces the cable’s ability to support Gigabit or faster Ethernet transmission.

Many homeowners install doorbell or security system wiring without any fire-stopping at wall and floor penetrations, assuming the small diameter of the cable makes it inconsequential. This assumption is incorrect: even a small cable penetration through a fire-rated assembly provides a pathway for smoke and hot gases, and the cumulative effect of multiple unstoppered low-voltage penetrations in a fire-rated wall can significantly compromise the assembly’s rated performance. All penetrations through fire-rated assemblies must be fire-stopped, regardless of cable size.

State and Local Amendments

California Title 24 adopts NEC provisions for low-voltage wiring with California amendments that are generally stricter than the base code in seismic requirements for conduit and cable supports. California also has specific provisions for fire alarm wiring that go beyond IRC 2024 in some residential applications, particularly in homes with monitored fire alarm systems as required by local wildfire risk area ordinances. Florida has specific requirements for hurricane-impact resistance that affect how cables are routed through exterior walls and penetrations, often requiring additional sealant or listed penetration systems at exterior penetrations to maintain the building envelope’s wind-driven-rain resistance.

Many municipalities have adopted local ordinances requiring that all new homes be pre-wired for structured data networks with a minimum number of drops per room and a central distribution panel. These local requirements go beyond IRC 2024, which establishes minimum safety standards but does not specify how many data outlets must be installed. Check local ordinances for structured wiring requirements when designing new construction.

When to Hire a Professional

Low-voltage wiring is within the capability of skilled DIYers for many applications — running data cable from a router to a room, installing a doorbell transformer and push button, or mounting a security camera and running its cable to a central hub. However, fire-stopping at rated-assembly penetrations requires licensed materials and proper installation technique, and incorrect fire-stopping is worse than no fire-stopping in some cases because it gives a false sense of security. For homes with structured media centers, multi-room audio systems with in-wall speaker wire, or whole-home automation wiring, a licensed low-voltage contractor will design and install the system with the correct cable types, proper separation from power wiring, and compliant fire-stopping throughout.

Common Violations Found at Inspection

• Data or security cables routed through the same drilled hole as NM-B power cable without a listed separator, violating the required separation between Class 2 and Class 1 wiring.
• Low-voltage cables entering the same box opening as power conductors in a shared wall plate without a listed barrier.
• Standard PVC-jacketed (CMR or CM rated) cable installed in a return-air plenum ceiling space where CMP-rated cable is required.
• Low-voltage cable penetrations through fire-rated floor-ceiling assemblies or fire separation walls not fire-stopped with listed materials.
• Data cables stapled with NM cable staples that are oversized for the cable diameter, crushing the cable jacket and potentially deforming the twisted pairs inside Cat 6 or Cat 6A cable.
• Data cable bent at sharp angles below the minimum bend radius at box entries or wall corners, compromising the cable’s transmission performance.
• Security system wiring in an attached garage penetrating the fire-separation wall to the living space without listed fire-stop material.
• Low-voltage cables left unsupported over long runs, sagging across ceiling joists without any stapling or support at code-required intervals.