Standard sizes for the various round electrical panel knockouts

Electrical panel knockouts and their corresponding hole sizes for drilling come in several standard sizes:

1. 1/2″ trade size: 7/8″ (22.5mm) hole2
2. 3/4″ trade size: 1-1/8″ (28.3mm) hole2
3. 1″ trade size: 1-3/8″ (34.6mm) hole2
4. 1-1/4″ trade size: 1-3/4″ (43.2mm) hole2
5. 1-1/2″ trade size: 2″ (49.6mm) hole2
6. 2″ trade size: 2-1/2″ (61.5mm) hole2
7. 2-1/2″ trade size: 3″ (74mm) hole2
8. 3″ trade size: 3-5/8″ (89.9mm) hole2
9. 3-1/2″ trade size: 4-1/8″ (102.7mm) hole2
10. 4″ trade size: 4-1/2″ (115.4mm) hole2

When drilling these holes, you can use either a hole saw or a conduit knockout punch of the corresponding size2. For example, for a 1/2″ trade size conduit, you would use a 7/8″ hole saw or a 1/2″ conduit knockout punch2.

It’s important to note that the trade size does not directly correspond to the actual hole size. The hole size is typically larger to accommodate the fittings and connectors used with the conduit.

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The difference between ‘trade size’ and actual size in electrical conduit is sigThe difference between ‘trade size’ and ‘hole size’ in electrical conduit and knockouts is significant:

1. Trade size: This is a standardized label used in the electrical industry to identify conduit sizes. It does not directly correspond to the actual physical measurements of the conduit or knockout3.
2. Hole size: This refers to the actual diameter of the hole that needs to be drilled or punched for the conduit to fit properly1.

For example:

• A 1/2″ trade size conduit requires a 7/8″ (22.5mm) hole1.
• A 1″ trade size conduit needs a 1-3/8″ (34.6mm) hole1.

The trade size system was developed to simplify conduit selection and ensure compatibility between components. However, it can be confusing for those unfamiliar with industry standards3.

Understanding this distinction is crucial for electricians and DIY enthusiasts when selecting the appropriate conduit size and drilling the correct hole size for their specific installation needs. The hole size is typically larger than the trade size to accommodate the fittings and connectors used with the conduit14.

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the hole sizes mentioned for electrical conduit also apply to knockouts needed for connectors and other fittings12. These standardized sizes ensure compatibility between conduits, connectors, and electrical boxes. For example:

1. A 1/2″ trade size conduit or connector requires a 7/8″ (22.5mm) knockout or hole.
2. A 1″ trade size conduit or connector needs a 1-3/8″ (34.6mm) knockout or hole.
3. A 1-1/4″ trade size conduit or connector fits into a 1-3/4″ (43.2mm) knockout or hole.

This standardization allows electricians to use the same knockout sizes for both conduits and their corresponding connectors, simplifying installation and ensuring proper fit. When working with electrical panels or boxes, the knockout sizes are designed to accommodate these standard trade sizes for conduits and connectors34.