What Are Reducing Washers?

Reducing washers are metal rings used in pairs to reduce a larger knockout or hole to accept a smaller conduit connector, hub, or fitting. In practice, they let you use an existing enclosure opening when the raceway size has changed or when the original knockout is larger than needed. They are commonly used with steel boxes, cabinets, and panel enclosures. A reducing washer set does not replace the actual connector or locknut. It works with those parts by stepping the opening down to the required size. On many jobs, they are chosen because they are faster and cleaner than replacing the box or trying to modify the opening in the field.

Where Are Reducing Washers Used?

Reducing washers are used in commercial, industrial, institutional, and maintenance work anywhere an enclosure opening is oversized for the raceway being installed. Typical examples include panelboard entries, junction boxes, pull boxes, wireways, disconnects, control panels, and retrofit equipment. They are especially common in service and renovation work where an existing knockout pattern does not match the new conduit layout. They can also be useful when standard enclosure knockouts are available only in larger sizes than the fitting being installed. In new work, they are often a convenience item. In retrofit work, they are often a problem-solving item.

How To Choose Reducing Washers

Start with the actual opening size in the enclosure and the trade size of the fitting or connector you need to install. Then confirm the washer set is intended to reduce from that larger opening to that smaller fitting size. Also check the enclosure material and thickness, because some combinations of locknut, bushing, and fitting body can become tight on thread engagement when multiple parts are stacked together. If bonding continuity matters, review whether the fitting and enclosure arrangement still provides the required grounding path. For wet or washdown locations, reducing washers may not be the right answer if a raintight or sealing method is required. In those cases, a hub, Myers style arrangement, or different enclosure entry method may be more suitable. For visible finished work, also consider whether the reduced opening will leave a neat appearance around the fitting.

Trade Rules Of Thumb

A common rule of thumb is that reducing washers are most useful when the enclosure opening is already there, the size reduction is straightforward, and the fitting still seats properly without forcing the assembly. Another practical rule is to avoid stacking improvised parts when a proper reducing washer pair is available for the exact size change. If the installation starts to require multiple adapters, unusual thread engagement, or uncertain bonding, it is usually worth stepping back and choosing a different fitting method. For service work, many electricians keep common reducing washer sizes on hand because they solve frequent panel and box entry issues quickly. These are practical trade habits, not code rules, and final suitability should always be checked against the equipment listing, fitting requirements, and local inspection expectations.

Sizing Guidelines

The key sizing point is that reducing washers are selected by the larger opening size and the smaller trade size being adapted. Verify both before ordering. Do not assume the knockout size stamped on an enclosure always matches what is present in the field, especially on older gear or modified boxes. Measure if there is any doubt. Also confirm that the connector, locknut, and any insulating or bonding bushing still have enough usable thread after the washer pair is installed. As a practical guideline, reducing one standard knockout size to the next smaller fitting size is usually straightforward, while larger step-downs deserve a closer look at fit, support, and finish. Where conductor protection, bonding, or environmental sealing is part of the design, those requirements should be reviewed together with the washer size selection.

Common Installation Practices

Typical installation uses one reducing washer on each side of the enclosure wall so the larger opening is captured and reduced evenly for the smaller fitting. The fitting is then installed through the reduced opening and secured with the appropriate locknut or other hardware. Installers usually check that the washers sit flat, do not distort the enclosure wall, and do not interfere with adjacent knockouts or hardware inside the box. In panel and cabinet work, it is also common to verify that the reduced opening does not crowd wire bending space or block covers and barriers. Good practice includes checking for sharp edges, maintaining bonding continuity where required, and using the correct bushing or connector type for the raceway and conductor method being installed.

Common Mistakes

One common mistake is ordering by conduit size alone without confirming the actual enclosure opening size. Another is assuming reducing washers solve every mismatch problem, even where a raintight hub, bonding fitting, or different enclosure entry method is needed. Installers also run into trouble when thread engagement becomes too short after adding washers, especially on thicker enclosure walls or when bushings are required. A further mistake is using reducing washers on damaged or irregular openings where the washer cannot seat properly. In retrofit work, it is also easy to overlook how the reduced fitting location affects conductor bending space, cover clearance, or locknut access. Most of these issues are avoidable if the opening, fitting stack-up, and enclosure conditions are checked before the raceway is installed.

Brand Comparisons

Bridgeport is widely recognized in the conduit fitting market and is commonly specified where contractors want a familiar trade brand with broad acceptance in standard commercial and industrial work. Hubbell is also a well-known name and may be preferred where buyers are already standardizing around Hubbell electrical products or want to align with an existing installed brand family. Ortech can be a practical value option for many routine applications where the goal is to complete standard box and enclosure reductions without overcomplicating the bill of material. T&B and Iberville are also commonly seen in the broader market, especially where matching existing fittings or enclosure hardware matters. In many cases, the right brand choice is less about brand loyalty and more about getting the correct size combination, finish, fit, and jobsite consistency. If a facility already uses one brand heavily, matching that installed base can simplify maintenance and replenishment.

Related Products

Reducing washers are often purchased with conduit connectors, locknuts, insulating bushings, bonding bushings, chase nipples, close nipples, hubs, box connectors, and enclosure accessories. For panel and cabinet entries, buyers may also need grounding hardware, sealing locknuts, or raintight fittings depending on the environment. In retrofit work, reducing washers are frequently part of a larger repair kit that includes knockout seals, locknuts, bushings, and short nipples so the installer can adapt whatever opening is found on site. If the application involves wireway, pull boxes, or control cabinets, it is worth reviewing the full entry assembly rather than treating the washer as a standalone item.

Frequently Asked Questions

Are reducing washers sold as a pair?

They are commonly used as a pair, with one washer on each side of the enclosure wall. Product packaging can vary, so it is worth confirming the listing and pack details before ordering.

Can reducing washers be used in panelboards and cabinets?

They are often used in panelboards, cabinets, and junction boxes when the opening is larger than the fitting being installed. Suitability still depends on the enclosure, fitting type, bonding method, and local code acceptance.

Do reducing washers provide bonding by themselves?

Do not assume that. Bonding depends on the full fitting assembly, enclosure type, and installation method. Where bonding is required, verify that the complete arrangement meets the project and code requirements.

Can I use reducing washers for outdoor or wet locations?

Sometimes, but not automatically. If the entry must be raintight or sealed, you need to confirm that the full assembly is suitable for that environment. In many outdoor applications, a different fitting method may be the better choice.

What is the most important measurement when ordering reducing washers?

The most important measurements are the existing enclosure opening size and the smaller trade size you need to adapt to. If there is any doubt, measure the field opening rather than relying only on assumptions from the drawing or enclosure label.