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18 Cu. In. Round Plastic Old Work Switch Box – With or Without Ground Clip
These 18 cubic inch round plastic switch boxes are designed for old work (retrofit) installations in existing walls or ceilings. Made from high-strength, non-metallic thermoplastic, they offer excellent durability, corrosion resistance, and electrical insulation.
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PSBR18-OW: Standard version with integrated mounting clamps for a secure and easy installation.
-
PSBR18G-OW: Same features as the standard model, but includes a grounding clip for use in grounded wiring systems.
| SKU Variant | Weight | Diameter | Height | Width | Depth | Length |
|---|---|---|---|---|---|---|
| PSBR18-OW | 0.22 lbs | 4.38″ | 4.38″ | 4.38″ | 2.68″ | — |
| PSBR18G-OW | 2.16 lbs | — | 4.38″ | 4.38″ | 2.68″ | 2.75″ |
Manufacturer Resources
PSBR18-OW
Product Specs
- Box Shape:
- Round
- Product Type:
- Switch Box
- Special Features:
- With Ground Lug (PSBR18G-OW)
- Application:
- Installing round electrical boxes in existing walls
- Cubic Capacity:
- 18 cu in
- Gang Options:
- 1-Gang
- Mounting Feature:
- Old Work
- Product Group:
- Electrical Boxes
- Product Subgroup:
- Junction Boxes
- Cable Entry:
- (4) Clamps
- Product Material:
- Plastic
- Department:
- Electrical
Centaur PSBR18-OW – Frequently Asked Questions
1) Can the Centaur PSBR18-OW round box be installed in an existing finished wall or ceiling?
Yes, that is exactly what it's built for. The PSBR18-OW is an old work (retrofit) box, so it mounts into drywall that is already up without needing access to a stud or joist face. Cut the round opening, feed the cable in, and the integrated clamps hold it against the back of the wallboard.
2) What is the difference between Centaur PSBR18-OW and PSBR18G-OW?
Same box, one added part. The PSBR18G-OW carries a grounding clip (ground lug) for grounded wiring systems; the PSBR18-OW is the standard version without it. Everything else, round plastic body, 18 cubic inch capacity, four clamps, old work mounting, is identical. If your circuit has an equipment ground to terminate at the box, order the G version.
3) What size hole do I cut for the Centaur PSBR18 round old work box?
The box body measures 4.38 inches across with a 2.68 inch depth, so cut to the 4.38 inch round profile and make sure you have at least 2.68 inches of clear cavity behind the drywall. Use the box itself or a matching round template to scribe the opening, an oversized cut leaves the clamps nothing to grip.
4) Is a plastic box like this OK where a metal box was pulled out?
Non-metallic thermoplastic is standard for NM cable work and gives you corrosion resistance and built-in insulation, but it does not serve as an equipment grounding path the way a metal box does. If the old metal box was being used to bond the system, pick the PSBR18G-OW with the ground lug so the equipment ground has a terminating point.
5) Can I hang a ceiling fan from the Centaur PSBR18-OW?
No. This is a standard old work plastic outlet box held by drywall clamps, not a fan-rated or fan-support box. Ceiling fans and any fixture over the normal weight limit need a listed fan-rated box with a brace or joist mount. Use this one for light fixtures and junction points only.
6) Is 18 cubic inches enough box fill for a ceiling fixture with a couple of cables?
18 cubic inches is the usable volume of this round Centaur box, and it is a 1-gang box. That volume governs how many conductors you can legally put in it under the NEC box fill rules, so count your conductors, clamps, and device allowances against 18 cu in before you commit. For a simple fixture outlet with two 14/2 or 12/2 cables it is generous; for a junction point with three or more cables plus a fixture, do the fill math first.
7) How does cable get into the Centaur round old work box, and do I need separate connectors?
Four built-in clamps handle the cable entries, so no add-on cable connectors are needed for NM cable. That is also why the clamps matter to your fill calculation, internal clamps count as one conductor volume allowance under the box fill rules.
8) Can I use this round Centaur box for a wall switch as well as a ceiling light?
It is a 1-gang round box rated for ceiling or wall use, so a single switch or receptacle works, but round boxes take a round cover or a device mounted on a round plate. For a standard rectangular switch plate in a retrofit wall, most electricians reach for an old work rectangular 1-gang box instead. The round profile is the better choice for fixture and fan-less ceiling outlets and for junction points.
9) Are these Centaur round old work boxes sold individually or by the case?
They ship 30 boxes per order, which is how most electrical contractors and MRO buyers want them for a multi-unit rough-in or a standing repair stock. The Standard and the With Ground Lug (G) versions are ordered separately, so decide which one you need before you place the order.
How fast can I get the Centaur PSBR18-OW delivered?
Most orders ship the same day from our distribution partners, with quick delivery throughout the
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Need it urgently? Contact Us for expedited shipping options.
Can I return it if it doesn’t work for me?
Yes—ZenSupply offers a hassle-free return policy. If the product isn’t the right fit,
reach out to our support team for a return authorization or setup a return by following our return instructions.
Does the Centaur PSBR18-OW come with a warranty?
Absolutely. The Centaur PSBR18-OW is backed by a manufacturer’s warranty.
For full warranty terms, check the product documentation or Contact Us.
How do I get technical support or installation help for the Centaur PSBR18-OW?
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