How to Use Armored (BX) Electrical Cable: A Comprehensive Guide

Armored cable, commonly known as BX cable, is a type of electrical wiring consisting of conductors insulated with paper or plastic and encased in a flexible metal sheath. This metal sheath provides physical protection to the conductors, making BX cable suitable for various applications where exposed wiring might be vulnerable to damage. This comprehensive guide will walk you through everything you need to know about using armored cable, from understanding its components and applications to safely installing it.

Understanding Armored (BX) Cable

Before diving into the installation process, it’s crucial to understand the components and characteristics of BX cable.

* **Conductors:** BX cable typically contains two or three insulated conductors. These are usually copper wires, although aluminum conductors are also available. The insulation is usually made of thermoplastic. The number of conductors and their gauge (thickness) determine the cable’s ampacity, which is the maximum current it can safely carry.
* **Bonding Strip (Aluminum or Copper):** A thin, uninsulated aluminum or copper bonding strip runs inside the armor along the conductors. This strip provides a continuous low-impedance path for grounding, helping to ensure safety in case of a fault. Modern armored cables often utilize the armor itself as the grounding means and may not always have a dedicated bonding strip.
* **Anti-Short Bushing (Red Head):** This small, typically red, plastic bushing is inserted between the cut end of the armor and the conductors to protect the conductor insulation from abrasion against the sharp metal edge. It’s a crucial safety component.
* **Metal Armor:** The interlocked metal sheath is the defining feature of BX cable. It provides excellent physical protection against impacts, abrasion, and crushing. This makes BX cable a good choice for locations where wiring might be exposed or subject to mechanical stress.

When to Use Armored Cable

BX cable is a versatile wiring option suitable for various applications. However, understanding its appropriate uses is essential.

* **Exposed Runs:** One of the primary advantages of BX cable is its suitability for exposed runs. It can be installed without conduit in locations where wiring might be visible or subject to physical damage, such as unfinished basements, garages, and attics.
* **Dry Locations:** BX cable is primarily designed for dry indoor locations. While some types of armored cable are available for wet or damp locations, standard BX cable should not be used in these environments.
* **Remodeling Projects:** BX cable is frequently used in remodeling projects because it can be easily fished through walls and ceilings without the need for rigid conduit.
* **Appliances:** It’s suitable for wiring appliances, especially those requiring grounding, such as water heaters, furnaces, and air conditioners.
* **Commercial and Industrial Settings:** Due to its durability, BX cable is commonly used in commercial and industrial settings for lighting, power circuits, and control systems.

Tools and Materials Required

Before starting your BX cable installation, gather the necessary tools and materials.

* **Armored Cable Cutter (Rotary or Pliers Type):** This specialized tool is designed to cut the metal armor of BX cable without damaging the conductors inside. A rotary cutter is generally preferred for its clean and efficient cuts.
* **Utility Knife:** A utility knife is handy for scoring the cable jacket and removing the paper wrap.
* **Screwdrivers (Various Sizes):** You’ll need screwdrivers to tighten screws on connectors, junction boxes, and electrical devices.
* **Pliers (Lineman’s Pliers, Needle-Nose Pliers):** Pliers are essential for various tasks, such as bending wires, stripping insulation, and making connections.
* **Wire Strippers:** Wire strippers are used to remove insulation from the ends of the conductors without damaging the wire.
* **Voltage Tester:** A non-contact voltage tester is a crucial safety tool for verifying that the power is off before working on any electrical circuit.
* **Electrical Tape:** Electrical tape is used to insulate and protect wire connections.
* **BX Cable Connectors:** These connectors are specifically designed to secure BX cable to junction boxes, electrical panels, and other enclosures. Use the correct size connector for the BX cable being used (typically 1/2″ or 3/4″).
* **Anti-Short Bushings (Red Heads):** As mentioned earlier, these bushings protect the conductor insulation.
* **Junction Boxes:** Junction boxes are used to house wire connections and provide a safe enclosure for splices.
* **Fish Tape (Optional):** If you need to run the cable through walls or ceilings, a fish tape can be helpful.
* **Safety Glasses:** Always wear safety glasses to protect your eyes from debris.
* **Gloves:** Wear gloves to protect your hands from sharp edges and electrical shock.

Step-by-Step Installation Guide

Follow these steps to safely and effectively install BX cable.

**Step 1: Safety First – Turn Off the Power**

Before starting any electrical work, the MOST important step is to turn off the power to the circuit you’ll be working on. Locate the circuit breaker or fuse that controls the circuit and switch it to the “off” position. Use a non-contact voltage tester to verify that the power is indeed off. Test the wires you plan to work on to ensure no electricity is flowing. **Double-check!** It’s better to be overly cautious than to risk electric shock.

**Step 2: Plan Your Cable Run**

Before cutting any cable, plan the route it will take. Determine the location of junction boxes, outlets, switches, or appliances that you’ll be connecting to. Measure the distances between these points to determine the required length of BX cable. Add a few extra feet of cable to allow for slack and connections.

**Step 3: Cut the Cable to Length**

Use an armored cable cutter to cut the BX cable to the desired length. There are two main types of cable cutters:

* **Rotary Cutter:** Place the cable in the cutter head and rotate the cutter around the cable, applying gentle pressure. Continue rotating until the armor is scored all the way around. Then, flex the cable back and forth at the score line until the armor breaks. The conductor insulation must NOT be cut.
* **Pliers-Type Cutter:** This type of cutter has a blade that pierces the armor. Squeeze the handles of the cutter to pierce the armor, then twist the cutter around the cable to cut the armor. Be careful not to damage the conductors.

**Step 4: Prepare the Cable End**

After cutting the armor, carefully bend the cut end back to expose the conductors. Be extremely careful not to damage the insulation on the wires. Use a utility knife to carefully score the outer paper or plastic wrap just behind where the armor has been cut and then remove the paper/plastic to expose the conductors and bonding strip. Be careful not to cut the conductors themselves.

**Step 5: Insert Anti-Short Bushing (Red Head)**

This is a critical step! Slide the anti-short bushing (red head) over the conductors and push it firmly into the end of the metal armor. Make sure the bushing completely covers the cut edge of the armor, protecting the conductor insulation from abrasion. The conductors MUST pass through the bushing.

**Step 6: Attach the Connector**

Insert the cable into the BX cable connector. The connector typically consists of two parts: a body that attaches to the junction box and a clamp that secures the cable. Slide the connector body over the cable, ensuring the anti-short bushing remains in place. Tighten the screws on the connector clamp to securely grip the cable. Do not overtighten, as this can damage the cable or connector.

**Step 7: Install the Connector in the Junction Box**

Insert the connector into the knockout hole of the junction box and secure it with a locknut. Tighten the locknut firmly to ensure a good electrical connection between the connector and the junction box. The grounding path through the armor and the connector to the metal box is vital for safety. Ensure a tight, secure connection.

**Step 8: Make Wire Connections**

Inside the junction box, strip the ends of the conductors using wire strippers. Connect the wires according to the wiring diagram for your specific application. Use wire connectors (wire nuts) to join the wires together securely. Make sure the connections are tight and properly insulated with electrical tape. Ensure all connections are made inside an approved junction box. NEVER leave exposed wire connections. Follow all applicable electrical codes.

**Step 9: Secure the Bonding Strip (If Applicable)**

If your BX cable has a separate bonding strip, connect it to the grounding terminal in the junction box. This provides a path for fault current to flow back to the source, helping to trip the circuit breaker and prevent electrical shock. Wrap the bonding strip around the ground screw in the box and tighten it securely.

**Step 10: Secure the Cable Runs**

Secure the BX cable runs to the building structure using cable staples or clamps. Space the supports according to the electrical code requirements (typically every 4.5 feet horizontally and within 12 inches of any box or fitting). Do not overtighten the staples or clamps, as this can damage the cable. Do not bend the cable at too sharp an angle; maintain a smooth, gradual bend radius.

**Step 11: Test the Circuit**

After completing the wiring, carefully inspect all connections to ensure they are secure and properly insulated. Turn the circuit breaker back on. Use a voltage tester to verify that the circuit is working correctly. Test any outlets, switches, or appliances connected to the circuit.

Important Considerations and Safety Tips

* **Local Electrical Codes:** Always comply with all applicable local electrical codes. These codes vary from place to place and are designed to ensure electrical safety. Consult with a qualified electrician if you have any questions about the code requirements in your area.
* **Proper Grounding:** Grounding is crucial for electrical safety. Ensure that all equipment and devices are properly grounded. Never defeat the grounding system.
* **Overcurrent Protection:** Use the correct size circuit breaker or fuse for the circuit. Overcurrent protection devices are designed to protect the wiring from overheating and causing a fire.
* **Wet or Damp Locations:** Standard BX cable is not suitable for wet or damp locations. Use a special type of armored cable that is specifically designed for these environments, such as MC cable with a waterproof jacket.
* **Underground Use:** Do not use standard BX cable for underground installations. Use a cable that is specifically designed for underground use, such as UF cable.
* **Working in Confined Spaces:** When working in confined spaces, such as attics or crawl spaces, take extra precautions to ensure your safety. Wear appropriate protective gear, such as a dust mask and gloves. Make sure the area is well-ventilated.
* **Aluminum Conductors:** If you are using BX cable with aluminum conductors, use connectors that are specifically designed for aluminum wire. Aluminum wire requires special connectors to prevent corrosion and ensure a good electrical connection.
* **Call a Professional:** If you are not comfortable working with electricity, or if you have any doubts about your ability to safely install BX cable, call a qualified electrician. It’s always better to be safe than sorry.
* **Don’t Overload Circuits**: Ensure that the circuit you are wiring is not overloaded. Overloaded circuits can cause the breaker to trip frequently and can pose a fire hazard. Calculate the total load on the circuit before adding any new devices.
* **Use the Correct Gauge Wire:** The gauge of the wire must be appropriate for the amperage of the circuit. Using wire that is too small can cause it to overheat and create a fire hazard. Consult an ampacity chart to determine the correct wire gauge for your application.
* **Inspect Existing Wiring**: Before making any connections to existing wiring, inspect it carefully for damage or deterioration. Replace any damaged or worn wiring.
* **Labeling**: Clearly label all circuits and junction boxes. This will make it easier to identify and work on the circuits in the future.

Troubleshooting Common Issues

* **Circuit Breaker Tripping:** If the circuit breaker trips frequently, it could be due to an overloaded circuit, a short circuit, or a ground fault. Check the wiring for any signs of damage or loose connections. Reduce the load on the circuit or replace the circuit breaker if necessary.
* **Outlets Not Working:** If an outlet is not working, check the circuit breaker. If the breaker is not tripped, check the wiring connections at the outlet and in the junction box. Use a voltage tester to verify that there is power at the outlet.
* **Lights Flickering:** Flickering lights can be caused by loose connections, a faulty switch, or voltage fluctuations. Check the wiring connections at the light fixture and switch. Replace the switch if necessary.
* **Warm Outlets or Switches:** If an outlet or switch feels warm to the touch, it could be a sign of an overloaded circuit or loose connections. Turn off the power to the circuit and check the wiring connections. Replace the outlet or switch if necessary.

Alternatives to BX Cable

While BX cable is a reliable option, other types of cable might be more suitable for specific applications.

* **NM Cable (Nonmetallic Sheathed Cable or Romex):** NM cable is commonly used for residential wiring. It consists of insulated conductors wrapped in a plastic sheath. NM cable is less expensive than BX cable but does not provide the same level of physical protection. It is only suitable for dry, interior locations.
* **MC Cable (Metal-Clad Cable):** MC cable is similar to BX cable but has a heavier-duty metal sheath. It is suitable for both exposed and concealed locations and can be used in dry, damp, or wet locations, depending on the type of MC cable.
* **UF Cable (Underground Feeder Cable):** UF cable is designed for direct burial underground. It has a waterproof jacket that protects the conductors from moisture and corrosion.
* **Conduit:** Conduit is a rigid or flexible metal or plastic tube used to protect electrical wiring. Conduit provides excellent physical protection and is often required in commercial and industrial settings.

Conclusion

Armored (BX) cable is a durable and versatile wiring option suitable for various applications. By following the steps outlined in this guide and taking the necessary safety precautions, you can safely and effectively install BX cable in your home or business. Always remember to consult with a qualified electrician if you have any questions or concerns. Understanding the proper use of armored cable contributes significantly to a safe and functional electrical system.