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

Armored cable, often referred to as BX cable, is a type of electrical wiring that encases conductors in a flexible metal sheath. This metal armor provides a degree of physical protection to the conductors, making it a popular choice for both residential and commercial electrical installations. While less common than NM-B (Romex) cable in new residential construction, BX cable remains a viable option, particularly for exposed wiring runs or situations where greater protection is needed. However, working with BX cable requires specific techniques and adherence to electrical codes to ensure a safe and reliable installation. This comprehensive guide will walk you through the process of safely using armored electrical cable, covering everything from choosing the right cable to making proper connections.

Understanding Armored Cable (BX)

Before diving into the installation process, it’s crucial to understand the different types of armored cable and their applications. BX cable isn’t *exactly* the right term anymore; it’s more accurately referred to as AC (Armored Cable). However, the term BX is still commonly used, and most people will understand what you mean. We’ll use both terms interchangeably here.

* **AC (Armored Cable):** This is the most common type. It consists of insulated conductors wrapped in a flexible metal armor. It typically includes a bonding strip (a thin, uninsulated wire) inside the armor to help maintain ground continuity.
* **MC (Metal-Clad Cable):** MC cable is similar to AC cable but often has a thicker metal sheath and may include an insulated grounding conductor instead of a bonding strip. It’s often used for heavier-duty applications.
* **HCF (Health Care Facilities) MC Cable:** Specifically designed for use in hospitals and other healthcare settings. It contains an additional insulated grounding conductor and features a low-smoke jacket to minimize the spread of toxic fumes in the event of a fire.

**Key Components of BX/AC Cable:**

* **Conductors:** The insulated wires that carry the electrical current. Common sizes include 14 AWG, 12 AWG, and 10 AWG, with varying numbers of conductors (typically 2 or 3 plus a ground).
* **Paper Wrapping:** Many AC cables have a paper wrapping around the conductors inside the armor. This helps protect the conductors from abrasion against the metal sheath.
* **Metal Armor:** The flexible metal sheath that provides physical protection to the conductors.
* **Bonding Strip:** A thin, uninsulated wire inside the armor that helps maintain ground continuity.

**Advantages of Using Armored Cable:**

* **Physical Protection:** The metal armor protects the conductors from damage, making it suitable for exposed wiring runs or areas where the cable might be subjected to physical stress.
* **Fire Resistance:** The metal sheath provides a degree of fire resistance, slowing the spread of flames.
* **Suitable for Dry Locations:** AC cable is primarily intended for dry, indoor locations.
* **Aesthetically Pleasing (Sometimes):** In some industrial or exposed applications, the look of AC cable can be considered aesthetically pleasing.

**Disadvantages of Using Armored Cable:**

* **More Difficult to Install:** Working with AC cable requires specific tools and techniques, making it more challenging to install than NM-B cable.
* **Higher Cost:** AC cable is generally more expensive than NM-B cable.
* **Not Suitable for Wet Locations:** AC cable is not suitable for wet or damp locations unless specifically designed and rated for such environments.
* **Potential for Sharp Edges:** The cut ends of the metal armor can be sharp and require careful handling and the use of anti-short bushings.

Tools and Materials You’ll Need

Before starting any electrical work, gather the necessary tools and materials. Safety is paramount; always disconnect the power to the circuit you’ll be working on at the breaker panel before starting any work.

* **Armored Cable Cutter (Rotary Cutter):** This specialized tool is designed to cut the metal armor of the cable without damaging the conductors inside. A hacksaw *can* be used, but it’s much more difficult and increases the risk of damaging the wires. Rotary cutters are highly recommended.
* **Screwdrivers:** A variety of screwdrivers (Phillips and flathead) will be needed for connecting wires to devices and securing boxes.
* **Wire Strippers:** Used to remove the insulation from the ends of the wires without damaging the conductors.
* **Pliers:** For bending and manipulating wires, as well as tightening connectors.
* **Lineman’s Pliers:** A heavy-duty type of pliers useful for cutting and twisting wires.
* **Voltage Tester:** To verify that the power is off before working on any electrical circuit. *Always* double-check!
* **Electrical Tape:** For insulating connections and marking wires.
* **Fish Tape (Optional):** Helpful for pulling cable through walls or conduit.
* **Drill and Drill Bits:** For creating holes for mounting boxes and running cable.
* **Hammer:** For securing boxes and staples.
* **Level:** To ensure boxes are mounted straight.
* **Anti-Short Bushings (Redheads):** These plastic bushings are essential for protecting the conductors from the sharp edges of the cut metal armor. They *must* be used.
* **AC Cable Connectors:** These connectors are used to secure the AC cable to electrical boxes. Make sure you use the correct size connector for the cable you’re using. Common types include clamp connectors and set-screw connectors.
* **Electrical Boxes:** Metal or plastic boxes are used to house electrical connections and devices. Choose the appropriate size and type of box for the application.
* **Wire Connectors (Wire Nuts):** Used to join wires together securely. Choose the appropriate size for the number and gauge of wires you’re connecting.
* **Grounding Pigtails (Optional):** Short lengths of wire used to connect devices to the grounding system.
* **Armored Cable (BX/AC Cable):** Choose the appropriate gauge and number of conductors for the circuit you’re installing.
* **Safety Glasses:** Protect your eyes from flying debris.
* **Gloves:** To protect your hands.

Step-by-Step Guide to Using Armored Cable

Follow these steps carefully to ensure a safe and compliant installation.

**Step 1: Planning Your Wiring Run**

* **Determine the Circuit Requirements:** Calculate the amperage required for the devices you’ll be powering. This will determine the appropriate gauge of wire to use. Consult the National Electrical Code (NEC) or a qualified electrician if you’re unsure.
* **Plan the Route:** Map out the route the cable will take, ensuring it complies with all applicable codes and regulations. Avoid running cable through areas where it could be easily damaged.
* **Choose the Right Cable:** Select the appropriate type and size of armored cable for the application. Consider the environmental conditions and the load requirements.
* **Select Boxes and Connectors:** Choose the appropriate electrical boxes and connectors for the cable and the devices you’ll be connecting. Ensure the boxes are adequately sized to accommodate the wiring.

**Step 2: Cutting the Armored Cable**

This is a crucial step where many beginners make mistakes. Using the proper tool and technique is essential.

* **Using an Armored Cable Cutter (Rotary Cutter):**
* Open the cutter and place the cable inside the jaws, aligning the cutting wheel with the point where you want to cut the armor.
* Close the cutter firmly, but not excessively tight. You want the wheel to score the metal, not cut through it immediately.
* Rotate the cutter around the cable several times, applying gentle pressure. You should feel the wheel scoring the metal. Listen for a slight grinding sound.
* After several rotations, carefully bend the cable back and forth at the scored point. The armor should break cleanly.
* If the armor doesn’t break cleanly, repeat the scoring process with slightly more pressure.
* **Using a Hacksaw (Not Recommended):** This method is significantly more difficult and riskier. Only use it if you absolutely have no other option.
* Secure the cable in a vise.
* Carefully saw through the metal armor, being extremely careful not to cut into the conductors inside.
* Use a very fine-toothed blade.
* Once you’ve almost cut through the armor, stop and carefully bend the cable back and forth until it breaks.

**Step 3: Preparing the Cable End**

* **Inspect the Cut End:** Examine the cut end of the cable for any sharp edges or burrs. Use pliers to smooth them out if necessary.
* **Insert Anti-Short Bushing (Redhead):** This is *absolutely essential*. The sharp edges of the metal armor can easily cut through the insulation of the conductors, causing a short circuit.
* Slide the anti-short bushing (redhead) over the conductors and into the end of the metal armor. Make sure it’s fully seated and covers all the sharp edges.
* Some types of bushings have a small tab that needs to be bent inward to secure it in place.
* **Prepare the Conductors:** Use wire strippers to carefully remove the insulation from the ends of the conductors, exposing about 1/2 inch of bare wire. Avoid nicking or damaging the conductors.

**Step 4: Installing Connectors and Connecting to Boxes**

* **Attaching the Connector:**
* Loosen the screws or clamp on the AC cable connector.
* Insert the cable end into the connector, ensuring the anti-short bushing is fully seated inside the connector.
* Tighten the screws or clamp securely, making sure the connector is firmly gripping the metal armor of the cable.
* **Connecting to the Electrical Box:**
* Remove the appropriate knockout from the electrical box.
* Insert the connector through the knockout hole and secure it to the box using the provided locknut. Tighten the locknut securely.
* Ensure the connector is properly grounded. This is typically achieved through the metal-to-metal contact between the connector, the box, and the grounding conductor.

**Step 5: Making Wire Connections**

* **Identify the Wires:** Determine the function of each wire (hot, neutral, ground). Typically, black is hot, white is neutral, and green or bare copper is ground.
* **Connecting Wires:**
* For connecting wires within the box, use appropriately sized wire connectors (wire nuts).
* Twist the bare ends of the wires together tightly in a clockwise direction.
* Screw the wire connector onto the twisted wires, ensuring it’s fully seated and the wires are securely held.
* For connecting devices (switches, outlets), follow the manufacturer’s instructions. Typically, the hot wire is connected to the brass-colored screw, the neutral wire to the silver-colored screw, and the ground wire to the green screw or grounding terminal.
* **Grounding:** Proper grounding is critical for safety. Ensure all metal boxes and devices are properly grounded.
* If the AC cable includes a bonding strip, connect it to the metal box using a grounding screw or clip. The bonding strip provides a path for fault current to return to the source, tripping the circuit breaker and preventing electrical shock.
* If the AC cable has an insulated grounding conductor, connect it directly to the grounding terminal in the box and to the grounding screws on the devices.
* Use grounding pigtails to connect devices to the grounding system if necessary.

**Step 6: Securing the Cable**

* **Support the Cable:** Secure the AC cable to building structures using cable staples or straps. Support the cable at intervals specified by the NEC (typically every 4.5 feet horizontally and within 12 inches of boxes or fittings).
* **Avoid Over-Tightening:** Do not over-tighten the staples or straps, as this can damage the cable. Ensure the cable is securely supported but not crushed.
* **Protect from Damage:** Protect the cable from physical damage by running it through conduit or using guard strips in areas where it might be exposed to impact.

**Step 7: Testing and Inspection**

* **Visual Inspection:** Carefully inspect all connections and wiring to ensure they are properly made and that there are no loose wires or exposed conductors.
* **Continuity Testing:** Use a multimeter to check the continuity of the grounding system. Ensure there is a continuous ground path from the metal boxes and devices back to the grounding electrode system.
* **Voltage Testing:** After restoring power to the circuit, use a voltage tester to verify that the voltage is correct at the outlets and devices.
* **Final Inspection:** Have a qualified electrician inspect the installation to ensure it complies with all applicable codes and regulations.

Important Safety Considerations

* **Always Disconnect Power:** Before working on any electrical circuit, always disconnect the power at the breaker panel.
* **Verify Power is Off:** Use a voltage tester to verify that the power is off before touching any wires or components.
* **Wear Safety Gear:** Always wear safety glasses and gloves when working with electrical wiring.
* **Follow Electrical Codes:** Ensure all work complies with the National Electrical Code (NEC) and local electrical codes.
* **Use Approved Materials:** Only use electrical materials that are approved for the intended application.
* **Proper Grounding:** Proper grounding is essential for safety. Ensure all metal boxes and devices are properly grounded.
* **Don’t Overload Circuits:** Avoid overloading electrical circuits, as this can cause overheating and fires.
* **If You’re Unsure, Consult an Electrician:** If you’re not comfortable working with electrical wiring, consult a qualified electrician.

Common Mistakes to Avoid

* **Skipping the Anti-Short Bushing:** This is a critical safety component. Never omit the anti-short bushing (redhead).
* **Damaging Conductors:** Be careful not to nick or damage the conductors when stripping the insulation or cutting the cable armor.
* **Loose Connections:** Ensure all wire connections are tight and secure.
* **Improper Grounding:** Proper grounding is essential for safety. Follow all grounding requirements.
* **Using the Wrong Type of Cable:** Select the appropriate type of cable for the application and environmental conditions.
* **Ignoring Electrical Codes:** Ensure all work complies with the NEC and local electrical codes.

Alternatives to Armored Cable

While AC cable is suitable for many applications, other wiring methods may be more appropriate in certain situations.

* **NM-B (Romex) Cable:** The most common type of wiring used in residential construction. It’s less expensive and easier to install than AC cable, but it’s not as durable and is not suitable for exposed wiring runs.
* **EMT Conduit:** Electrical Metallic Tubing (EMT) is a thin-walled steel conduit that provides excellent physical protection for conductors. It’s often used in commercial and industrial applications.
* **Rigid Conduit:** Rigid metal conduit provides the highest level of physical protection for conductors. It’s used in harsh environments or where the wiring is subject to severe impact.

Conclusion

Using armored electrical cable can provide a durable and reliable wiring solution, especially in situations where physical protection is needed. However, it’s crucial to follow the proper techniques and safety precautions to ensure a safe and compliant installation. By understanding the different types of armored cable, using the appropriate tools, and carefully following the steps outlined in this guide, you can confidently and safely install AC cable in your home or business. Remember, if you’re ever unsure about any aspect of electrical work, consult a qualified electrician. Electrical work can be dangerous, and it’s always better to be safe than sorry.