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When performing a low-voltage cable installation, it's important to know what type of cable to use based on the space. Different areas and spaces require different cables, and because sometimes substitutions are necessary, knowing whether you can substitute one cable for another is essential.
Choosing the right low-voltage cable ensures that your installations are safe and that you'll avoid potential problems down the road. Because cable ratings and substitutions involve several factors, depending on the application, there are a few key characteristics to consider when choosing cable for your next project.
What are the types of fire-rated cable?
Most low-voltage cable is grouped into three fire safety categories: plenum cable, riser cable and general-purpose cable. Each category is constructed to a fire-resistance standard with specific flame resistance and smoke release characteristics and is tested for performance in specific environments.
1. Plenum cable
Plenum cables are the highest rated in terms of fire resistance because of where they are typically used.
A plenum is a space in a building, often between the ceiling and the roof or next floor, that's used for air circulation for heating, ventilation and air conditioning. Because smoke from burning cables in a plenum space could easily be sucked into the HVAC system and then spread throughout the building, you must use plenum cables instead of the less fire-resistant riser or general-purpose cables.
Plenum cables use conductor insulation and jacket materials that provide a higher degree of fire resistance and emit less smoke compared to other plastic materials.
2. Riser cable
Riser cables meet fire resistance standards for installation within a vertical riser, a run that spans more than one level of a building, or within an area that's specifically designated as a non-plenum environment. A riser is a vertical shaft or a series of rooms within a building that allow primary utilities like electrical conduits, water supply lines and communications cabling to be installed vertically.
Riser spaces are self-contained and not used for recirculating air to the HVAC system, so fire resistance requirements for these spaces are less stringent than for plenum spaces. Riser cables are constructed primarily to prevent the spread of fire vertically from one story in a building to another.
3. General purpose cable
General purpose cables are designed to be used in general purpose spaces. Because of this, they are not built to the same fire resistance standards as plenum or riser cables, making them the least fire resistant of these three cable categories and typically the least expensive.
We know sometimes substitutions are necessary due to budget or other constraints, but making the wrong substitution could be dangerous or illegal. Always defer to the local authority having jurisdiction (AHJ) to determine installation requirements and what substitutions are permissible. Most electrical codes in the United States are based on the National Electrical Code, which does permit certain substitutions.
General guidelines to follow:
Because plenum cables meet the highest fire-resistance standards of the three categories, plenum cable can be used in place of riser cable or general-purpose cable.
As the second most fire resistant of the three, riser cable can be used in place of general-purpose cable but not in place of plenum cable.
Since general-purpose cable is the least fire-resistant type, it cannot be installed as a substitution for riser cable or plenum cable.
Because plenum cables can be used in place of riser and general-purpose cables, some dealers choose to simplify their operations and reduce risk of inspection failures by standardizing on plenum cables for all installations. However, because it’s designed for greater fire resistance and smoke emission, plenum cable is also more expensive. For installations where you only need general-purpose cable, installing plenum can increase your material budget.
Installing the wrong type of cable for a project can result in severe damage due to fire. This can lead to large financial loss for the customer and a ruined reputation for you. Even more serious, it could lead to legal consequences and potential injuries or loss of lives.
If you need help choosing low-voltage cable for your next project, contact our Systems Design team.