Molly Ayala
Trade size is a measure of the diameter of a component wire, also used in light-duty chain. It is a nominal size, meaning it is what the item is referred to in size, rather than its actual dimension. For example, 1/2 EMT has an outside diameter of 0.706, an inside diameter of 0.622, and is 0.500 thick. Trade sizes vary depending on the material and trade, such as plumbing, electrical, HVAC, or woodworking. In the context of electrical boxes, trade size refers to the diameter of the component wire used in the box. Electrical boxes, also known as junction boxes, enclose wire connections and protect against short circuits and bad weather. They come in various shapes and sizes depending on their purpose and installation needs.
Characteristics and Values of Trade Size in Electrical Boxes:
| Characteristics | Values |
|---|---|
| Definition | A measure of the diameter of the component wire. |
| Other Names | Wire Gauge, Nominal Size |
| Use | Used to refer to the size of an electrical box or component vs. the actual dimension. |
| Examples | 1/2" EMT is 0.706" on the outside and 0.622" on the inside. |
| Varies By | Trade (plumbing, electrical, HVAC, woodworking) and material (copper, wood, etc.). |
| Calculation | For straight pulls, the length is eight times the nominal diameter of the largest raceway (trade size). |
| Angle Pulls | Width of the box should be at least six times the trade diameter of the largest raceway plus the sum of the remaining raceways on the same wall. |
| Considerations | Locknuts, bushings, and the number of conductors affect the width, depth, and size of the box. |
| Standards | National Electrical Code (NEC), local building codes, and Texas SFM Electrical Code. |
| Types of Electrical Boxes | Junction box, handy box, new work box, old work box, ceiling box, etc. |
| Shapes | Rectangular, square ("double-gang box"), round, octagonal, and ceiling boxes. |
| Materials | Metallic or non-metallic (e.g., plastic, metal, or wood). |
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What You'll Learn
Trade size is a nominal size
"Trade size" is a nominal size, meaning it refers to the name of the size of an item rather than its actual dimensions. For example, a 1/2" EMT conduit has an outside diameter of 0.706", an inside diameter of 0.622", and is 0.500" thick. Trade sizes are used in various trades, including plumbing, electrical, HVAC, and woodworking, and the measurements can vary depending on the trade and the material. For example, with HVAC copper, the outside diameter is measured, while with plumbing, the inside diameter is used.
In electrical work, trade size typically refers to the diameter of the component wire or conduit. Conduit is named for the size of the bundle of wires that can safely pass through it rather than its own inside or outside diameter. This can be frustrating for those doing DIY electrical work, as it is not always clear what the actual dimensions of a conduit or other electrical component are. However, understanding the conventions can help ensure that matching conduit and straps are purchased.
When working with electrical boxes, also known as junction boxes, it is important to select the correct size to safely enclose the wire connections and protect against short circuits, which can cause fires. The National Electrical Code (NEC) and local building codes regulate the types of electrical boxes allowed and how they should be installed. The size of the box will depend on the number and size of conductors and fittings enclosed within it, and both the box volume and box fill must be calculated to determine the appropriate size.
For straight pulls in electrical boxes, where the raceway enters and exits on opposite sides, the length must be eight times the nominal diameter of the largest raceway. For angle pulls, where conductors enter one side and exit from a different side other than the opposite, the width of the box must be at least six times the trade diameter of the largest raceway plus the sum of the remaining raceways on the same wall. The depth of the box should also take into account the dimensions of the locknuts or locknuts of fittings and the bushings of the connected raceways.
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Trade size depends on the material
Trade size is a measure of the diameter of a component wire. It is also used in light-duty chains, where it is referred to as "Wire Gauge". For example, 18 = 18, 16 = 16, and so on. Trade size is also used in the context of electrical boxes, which are also known as junction boxes.
The trade size of an electrical box is dependent on the material of the box and its intended use. Electrical boxes are available in a variety of shapes and sizes to fit different installation needs. The most common shape is a standard rectangle, which houses a single electrical switch or outlet and comes in metal or non-metallic units. Square electrical boxes, or "double-gang boxes", house two devices, such as a combination of outlets and switches. Round or octagonal boxes are used for lightweight fixtures or safety devices in the ceiling, such as lights or smoke alarms. Ceiling boxes are designed for heavier fixtures, like ceiling fans or chandeliers, and need to be made from materials that can support extra weight.
The material of an electrical box is also important to consider when determining trade size. Electrical boxes are typically constructed from metallic or non-metallic materials. Plastic electrical boxes, for example, are inexpensive and easy to install, but can only be placed behind drywall and used with non-metallic cables.
Additionally, the type of electrical box, such as a handy box, junction box, new work box, or old work box, will also determine the appropriate trade size. For example, a handy box is mounted on the surface of a wall and can contain light switches or receptacles, whereas a junction box allows circuits to split and branch in different directions.
When selecting an electrical box, it is important to refer to the National Electrical Code (NEC) and local building codes, which regulate the types of electrical boxes allowed for specific applications and their installation requirements.
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Trade size and the National Electrical Code
Trade size is a measure of the diameter of a component wire. It is also used in light-duty chain. Trade sizes are used in a variety of trades, including plumbing, electrical, HVAC, and woodworking. The term "trade size" is often used in reference to electrical boxes, also known as junction boxes, which enclose wire connections and protect against short circuits and fires.
The National Electrical Code (NEC) contains regulations that must be followed when choosing, installing, and sizing junction boxes. These regulations specify the required junction box size based on the number and size of conductors and fittings enclosed within the box. The NEC also outlines the minimum dimensions for different types of installations, such as angle or straight raceway runs.
When calculating the size of a pull or junction box, the cubic inch rating of each conductor must be multiplied by the number of conductors based on each cubic inch rating. This total cubic inch rating is then used to determine the appropriate box size. For example, an 8-by-8-by-4-inch box can house conductors with a calculated cubic inch rating of 256.
The NEC also specifies the minimum distance between raceways that contain the same connector. This distance must be at least six times the trade size of the largest raceway, measured from the near edge to the near edge of the raceway entries. For straight pulls, where the raceway enters and leaves on opposite sides of the box, the length must be eight times the nominal diameter of the largest raceway.
It is important to always reference the NEC when selecting the appropriate size and type of electrical box for a particular installation. This ensures compliance with safety regulations and helps prevent hazardous conditions.
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Trade size and junction boxes
Trade size is a measure of the diameter of the component wire. It is also used in light-duty chain, where it is synonymous with wire gauge. Trade sizes are often used in electrical work, including electrical boxes, also known as junction boxes.
Junction boxes are electrical enclosures that protect electrical conductors at the points where they are spliced, tapped, and pulled. They are typically made of metallic or non-metallic materials and come in various shapes and sizes. The size of a junction box is important to ensure that it can accommodate all the necessary conductors and fittings. If a junction box is too small, it can lead to excessive bending of conductors, potentially damaging the insulation on the wires.
When sizing a junction box, it is crucial to consider the number and size of conductors and fittings that will be enclosed within it. The National Electrical Code (NEC) provides regulations and guidelines for selecting the appropriate size box, ensuring compliance with safety standards. The NEC requires that the box has enough space for the conductors and that the dimensions of locknuts, bushings, and fittings are considered to avoid extending beyond the wall of the box.
The type of pull, whether straight or angle, also determines the size of the junction box. For a straight pull, the length of the box should be eight times the nominal diameter of the largest raceway (trade size). In contrast, for an angle pull, the width of the box should be at least six times the trade diameter of the largest raceway, plus the sum of the remaining raceways on the same wall.
It is important to note that trade sizes may not always correspond directly to the actual dimensions of the component. Therefore, it is advisable to refer to sizing charts or seek guidance from professionals to ensure compliance with electrical codes and safety standards.
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Trade size and metric designators
Trade size is a measure of the diameter of the component wire. It is also used in light-duty chain. Trade size is also referred to as wire gauge. For example, 18 = 18, 16 = 16, and so on. Trade size is not the same as the actual size of the component. For instance, 1/2" EMT is 0.706" on the outside, 0.622" on the inside, and 0.500" nowhere.
The term "trade size" is used in various trades, including plumbing, electrical, HVAC, and woodworking. The way things are measured differs between these trades and have changed over time. For example, with HVAC copper, the outside diameter is measured, while with plumbing, the inside diameter is measured. With wood dimensional lumber, the measurement is based on the outside dimensions.
The National Electrical Code (NEC) contains regulations that must be followed when choosing, installing, and sizing junction boxes. These regulations specify the required junction box size based on the number and size of conductors and fittings enclosed within the box. The NEC also specifies the minimum distance between raceways containing the same connector, which must be at least six times the trade size of the largest raceway.
The Texas SFM Electrical Code 2023 outlines the metric designators and corresponding trade sizes for conduit, tubing, and related fittings. These designators and sizes are for identification purposes only and do not represent actual dimensions. For example, Metric Designator 12 corresponds to a trade size of 3/8.
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Frequently asked questions
Trade size is a measure of the diameter of the component wire. It is also used in light-duty chain. Trade size is also referred to as wire gauge.
Electrical boxes, also known as junction boxes, enclose wire connections. They come in various shapes and sizes to fit different installation needs.
The shape of an electrical box can indicate its purpose. A standard rectangular box is the most common type, housing a single electrical switch or outlet. A square box, or double-gang box, houses two devices. Round or octagonal boxes are for ceiling lights or safety devices like smoke alarms. Ceiling boxes are for heavier fixtures like fans or chandeliers.
Electrical boxes provide protection against short circuits, bad weather, accidental contact, and tampering, which can cause wiring damage or fires. They also allow electricians to easily access conductors to perform work.
The size of the electrical box depends on the number and size of conductors and fittings enclosed within. You need to calculate both the box volume and box fill. The National Electrical Code (NEC) contains key regulations for choosing, installing, and sizing electrical boxes.
