COMMERCIAL ELECTRICAL MATERIALS Apprentice Electricians Should Know

Brendan Lamothe

Key Takeaways

  • 1900 boxes and their variations are essential in commercial setups.
  • MC connectors and MC cables are widely used for their strength and durability.
  • Familiarity with conduit fittings and electrical components is crucial for effective work.

Overview of Commercial Electrical Materials

When starting out in commercial electrical work, you'll frequently encounter various electrical materials. The 1900 box is a staple. It's versatile, used for housing devices like receptacles or switches, and for creating junction points for wiring. The industrial cover fits over the 1900 box, giving it a clean finish when mounted on a wall.

Next, mud rings are essential. They come in different depths and allow you to hide wiring behind sheetrock while still being able to mount devices. Moving on, a bracket box is similar to a 1900 box but includes brackets for easy mounting on studs.

Gangable boxes allow for configuration by removing side plates, letting you create multiple-gang boxes as needed. These can be tricky to install correctly, but you'll use them often.

For connecting cables, you'll use MC connectors, both single and double barrel types. These connectors lock cables in place securely. Alongside these connectors, you'll handle MC cable, which is preferred for its durability and rigidity.

Conduit fittings are another common item, including connectors for ending runs at boxes and couplings for joining lengths of conduit. You'll need to identify different styles based on application needs, such as rain-tight or set screw types.

Blanks, like the 1900 blank, are used to cover boxes that won't house a device, securing the wires within. Larger setups might require a 12 x 12 junction box, offering more space and built-in stab-ins for MC cable.

Lastly, you'll work with relays frequently in commercial projects, necessitating a solid understanding of their operation and application in various electrical systems.

Common Commercial Electrical Boxes

1900 Box

A 1900 box is a versatile box commonly used in commercial electrical work. It's known for its various knockouts around the sides, allowing you to bring in multiple wires. Whether for holding a receptacle or switch, or simply serving as a junction box, you'll find yourself using the 1900 box frequently.

Industrial Cover for 1900 Box

The industrial cover fits perfectly on a 1900 box, providing a neat and professional appearance once mounted on a wall. This cover is essential for securing and protecting the internal wiring and devices housed within the box.

Mud Ring

Mud rings come in various sizes and depths, designed to be used with 1900 boxes. They are especially useful when planning to cover your installation with sheetrock. By allowing the box to be recessed, the mud ring ensures a clean finish for your receptacles or switches.

Bracket Box

The bracket box is essentially a 1900 box with added brackets. These brackets allow you to mount the box securely to a stud or other structures. This type of box is known by multiple names such as a four-square or 4 x 4 x 1, depending on the regional terminology.

Gangable Box

A gangable box, also referred to as a cut-in or pop-in box, allows you to gang multiple boxes together by removing the screws and plates on the sides. These boxes are useful when you need to expand to three, four, or more gangs. Although they can be challenging to install, especially behind sheetrock, their flexibility makes them a staple in commercial electrical setups.

MC Connectors

Single Barrel MC Connector

Single barrel MC connectors are designed for a single piece of MC cable. The cable wires extend out from the sheathing, which snaps and locks in place. You simply knock out a hole in the box, snap the connector in, and run your wire through it. These connectors come in various styles, including snap-in types and those with lock rings for more secure fastening.


  • Single cable capacity
  • Snap-in or threaded with lock ring options
  • Easy installation and secure locking

Double Barrel MC Connector

Double barrel MC connectors accommodate two cables simultaneously. Like single barrel connectors, they come in different styles. Some snap into place, while others use a lock ring for a threaded and secure fit. Double barrel connectors are essential for situations requiring more complex wiring setups.


  • Dual cable capacity
  • Multiple installation styles (snap-in, threaded)
  • Ideal for more complex wiring needs

Connector Type


Installation Style

Single Barrel

1 cable

Snap-in or threaded

Double Barrel

2 cables

Snap-in or threaded

Knowing these MC connectors will streamline your work in commercial electrical setups.

MC Cable

MC Cable, or Metal-Clad Cable, is a type of electrical cable that is widely used in commercial settings. The primary difference between MC Cable and other types like Romex is the sheathing. MC Cable features a more rigid and durable metal sheathing, making it better suited for environments where it may be subject to physical damage.

The conductors inside MC Cable are similar to those found in Romex, but the robust exterior provides additional protection.

Types of MC Cable

  • Standard MC Cable: Composed of insulated conductors enclosed in a metal sheath.
  • MC-PCS Cable: Includes power and control signal cables, often used for dimming and lighting control circuits.
  • Armored MC Cable: Has an added layer of armor for maximum durability.


MC Cable is ideal for:

  • Commercial Buildings: Because of its durability and resilience.
  • Industrial Environments: Where cables may be exposed to potential physical harm.
  • Residential Use: In certain cases, depending on local electrical codes and regulations.

Installation and Use

When installing MC Cable:

  • Use MC Connectors to secure and terminate the cable.
  • Choose between snap-in connectors and threaded connectors based on your preference and the application.
  • Handle with care to avoid damaging the metal sheath which protects the internal conductors.

MC Cable provides a reliable and robust solution for a wide range of electrical installations. Understanding its applications and proper installation methods helps ensure safe and efficient electrical system setups in both commercial and residential environments.

Conduit Fittings


Connectors are essential for attaching conduit to boxes or other fittings. There are various types, including:

  • Single Barrel MC Connectors: Designed for a single piece of MC cable.
  • Double Barrel Connectors: Allow for two cables.
  • Snap-in Connectors: Feature a locking mechanism that clicks into the knockout hole on the box.
  • Threaded Connectors: Require a lock ring to secure them in place.


Couplings join two lengths of conduit together. Key types include:

  • Compression Couplings: Fit tightly together without the need for threading.
  • Set Screw Couplings: Use screws to fasten the conduit.
  • Rain Tight Couplings: Suitable for outdoor environments to prevent moisture ingress.

Knowing the differences between connectors and couplings will help streamline your work in various scenarios.

Covers for Electrical Boxes

1900 Blank Cover

A 1900 blank cover secures over a 1900 box, especially when there is no device installed inside. This type of cover is essential for making secure, tidy joints inside the box.

  • Appearance: Flat, sturdy metal or plastic with pre-drilled holes for mounting.
  • Usage: Cover boxes where only wire joints are made, without devices like switches or outlets.
  • Installation: Aligns with the 1900 box’s mounting holes and is fastened with screws.

Make sure to have both 1900 blank covers and device covers on hand to maintain covered, safe connections in all situations.

Electrical Components


Relays are integral components in commercial electrical systems. They function as electrically operated switches, allowing you to control a circuit using a low-power signal. This is essential for automating various electrical tasks.

Relays typically consist of:

  • Coil
  • Armature
  • Switching Contacts

When the coil is energized, it generates a magnetic field, pulling the armature and changing the state of the contacts. This simple mechanism is versatile and useful in many applications.

Types of Relays

  • Electromechanical Relays: Utilize mechanical movement to open or close contacts.
  • Solid State Relays: Use semiconductor devices to switch without mechanical movement, providing longer life and faster switching.

Common Uses

  • Lighting Control: Automated control of lighting circuits.
  • Motor Starters: For starting and stopping motors.
  • Safety Systems: Implementing fail-safes and emergency stop functions.

Key Features

  • Contact Ratings: Ensure relays can handle the required current and voltage.
  • Response Time: Important for tasks requiring quick switching.
  • Durability and Longevity: Especially critical in high-use scenarios.

Understanding these basic aspects of relays will help you effectively implement and maintain them in commercial electrical work.