Rotary Dimmers by Forbes & Lomax

The Rotary Dimmer by Forbes & Lomax is a push-to-switch, rotate-to-dim lighting control based on the elegant nickel and brass switches of the 1930s. Rotary dimmers can be mixed with toggle switches, push buttons and outlets on the same plate.

Established in 1987, Forbes & Lomax is a UK-based heritage electrical brand recognized by architects and designers for refined switch and outlet design.

• Can I order online? Yes, if your lights are standard dimmable LED, you know the plate type and gang count, and the plate is 4 gang or under. Standard means a line voltage bulb or fixture that dims on its own, with no driver, transformer or power supply in the run. If there is one, the module is chosen by that device rather than the fixture, so check Electrical & LED Compatibility below.
• What should I confirm? Junction box depth and how many circuits run to the location. Your electrician will know both.
• Does the Painted or Invisible plate need finishing? Yes. The Painted plate is painted and the Invisible inner plate is papered or painted, both before the electrician fits them. Allow for it in the schedule.
• When should I request a custom quote? Drivers, transformers, 0-10 V, 5 gang or more, or anything you are unsure about should be confirmed by our sales team in order to ensure compliance and compatibility. Please reach out to us at contact@cassonhardware.com.
• Can I install it myself? No. Line voltage, licensed electrician only.

Full specifications, module ratings and installation requirements are below.

The dimmer mechanism is identical across all three plates. What differs is how the plate meets the wall, which finishes are offered, and what has to happen on site before the electrician fits it.

Metal

• Construction: Solid metal, finished by hand. Plate and knob are supplied in the same finish.
• Site Work: None. Fitted as supplied.
• Finishes: The full range. Aged Brass is the one exception, and applies to the plate only.

Invisible

• Top Plate: Transparent acrylic with bevelled edges, secured without visible fixing screws.
• Inner Plate: Primed aluminium, supplied ready to be papered or painted. Each unit ships with both plates.
• Wallpaper: The inner plate can be used as a template to cut a piece to fit.
• Over Stone or Tile: The inner plate can be faux painted to match the surrounding surface.
• Sequence: The inner plate is decorated as part of the wall finish, before the top plate goes on. Allow for it in the schedule rather than at handover.
• Finishes: Applied to the knob and screws only. Aged Brass is not offered.

Painted

• Construction: Etch-primed metal, supplied unpainted. The plate itself carries no metal finish.
• Method: Lay the plate flat and apply two to three coats with a small roller. Rolling, hand-painting and spraying each give a different look.
• Top Coat: A clear matte varnish can be applied to protect against marks.
• Glaze Paint: Undercoat the plate in the same colour as the walls.
• Sequence: Paint the plate separately and let it dry completely before fitting. Screw heads can be painted to match and touched in afterwards.
• Finishes: Applied to the knob only. Aged Brass is not offered.

Plate heights, widths and thicknesses are listed under Specifications below.

Selecting the Right Module

The module is set by what your fixture is and what drives it, not by wattage alone. Measure the total connected load on that dimmer, then select from the table.

• Supply: Line voltage, for conventionally wired installations.
• LED Module: Available to order online on all three plates.
• Specialty Modules: Incandescent, magnetic low voltage and 0-10 V are available in every finish and on every plate by request.
• Minimum Load: No formal minimum is stated for the LED module, however 5 W minimum is recommended in order for the dimmer to register that a fixture is connected.
• 0-10 V Wiring: A current-sinking signal dimmer. It connects to lighting drives through a Lutron PP-DV power pack or equivalent relay, purchased separately. All connections must be Class 2 and the install requires additional wiring beyond a conventional dimmer.
• Magnetic Low Voltage: For magnetic transformers only, 600 VA maximum with a 50 W minimum load. Must not be used with solid-state electronic low voltage.
• Electronic Low Voltage: Not supported. An ELV or reverse phase dimmer is not made in this range. Where a fixture requires one, a non-dimming toggle switch is the only option.

Dimming LED

Dimming LED is difficult across the whole lighting industry, not just this range. Compatibility can usually be predicted from a fixture's specification sheet, which is why we ask for it, but some trial and error is normal. Send your lighting schedule to contact@cassonhardware.com and we will review it with Forbes & Lomax.

• Compatibility Notice: There is no guarantee that every fixture labelled dimmable is suitable for smooth dimming on a TRIAC module. Performance depends on the make of fixture and the driver used. This is an industry standard and may require prior confirmation or testing.
• Dimming Range: Some flickering can occur at the top or bottom of the range, even on a compatible fixture. Optimizing the dimming range resolves most cases. See Installation below.
• Bulb Selection: For screw-in LED, Philips Ultra Definition is recommended. These dim smoothly to low levels and hold colour quality across the range.
• On-Site Testing: Where a fixture is unusual and certainty is needed before a full order, a single dimmer can be purchased and tested in position.
• Circuit Loading: One lighting type per dimmer. Recessed lights and a chandelier on the same circuit will perform poorly even where each is individually compatible.

• Electrician: Must be installed by a licensed electrician, in accordance with appropriate electrical codes and regulations.
• Wiring: Supplied as 3-way, works as single pole or 3-way. All modules wire conventionally except 0-10 V.
• Circuit Position: A rotary dimmer can be wired at only one position on a 3-way or 4-way circuit. Every other position must be a toggle or non-dimming rotary switch.
• Junction Box Depth: Recessed at least 1/8" below the finished wall surface. Refer to the Junction Box Assembly Diagram below. Check existing boxes before ordering.
• Plate Finishing: Painted and Invisible plates are decorated before the electrician fits them. Refer to Plate Overview above.
• Non-Dimming: Rotary switches are available on all three plates where a rotary style is wanted but only push on/off is required.
• Optimizing: The dimmer selects the correct dimming mode automatically once connected. Set the minimum and maximum levels for your fixtures, then apply the Program Lock. On a compatible fixture this resolves most flickering. Changing the mode by hand is a last resort, after optimizing has been tried.
• Momentary Switches: Not line voltage. They work only with home automation systems including Lutron Homeworks, Crestron, Savant, Vantage and Control 4.
• Areas of Application: Light-duty commercial, residential.

Plates of 5 gang or more, and any circuit with a driver, transformer or 0-10 V dimming, are quoted by our sales team. Send the following to contact@cassonhardware.com and we will price it against your schedule.

• Plate type: Metal, Invisible or Painted
• Fixture make and model for every light on the circuit, and the driver or transformer type if there is one
• Total connected wattage per dimmer
• Number of switching positions on the circuit
• Gang count and what else shares the plate
• Fittings finish
• Junction box depth on site

Plate Sizes

All plates are 4.53" (115 mm) high. Metal and Painted plates are 1.8 mm thick. The Invisible plate is a 3 mm acrylic top plate over a 1 mm primed inner plate.

Dimmers, toggle switches, push buttons and outlets can be mixed on the same plate. Multi-gang plates are supplied to accommodate as many devices as required. Contact us with your device schedule for a quote.

Device Dimensions

• Knob: Ø 0.79" (20 mm). One dimmer fits per gang of a standard junction box.

Fittings finish availability differs by plate. On the Metal plate the finish applies to the plate and knob together; on Invisible and Painted it applies to the fittings only.

• Aged Brass: A plate finish only. Aged Brass mechanisms are not made, so the knob and screws are supplied unlacquered brass and patina alongside the plate rather than matching on arrival.
• Living Finishes: Unlacquered Polished Brass and Aged Brass darken and develop a patina with handling and exposure. This is intended and not a defect, and variation between pieces is normal.
• Lacquered Finishes: Nickel Silver, Brushed Stainless Steel, Antique Bronze, Lacquered Brushed Brass and Matte Brass hold a consistent colour and will not change.
• Matte Brass: Carries a baked lacquer coating that resists fingerprints.
• Care: Wipe clean with a dry, non-abrasive microfiber cloth. Avoid chemical or alcohol-based cleaners.

• Rotary Dimmers: Conform to UL 1472, certified to CSA C22.2 No. 184.

Review and ensure all certifications are applicable for your local code.

Product Sheets

• Rotary Dimmer Cut Sheet
• Painted Switch Range Cut Sheet
• Plate Dimensions
• Forbes & Lomax Brochure

Module Documentation

• 120 W LED / 300 W Incandescent — Wiring
• 120 W LED — Optimization
• 120 W LED — Compatibility & Troubleshooting
• 500 W Incandescent / Halogen
• 600 VA Magnetic Low Voltage
• 0-10 V

Installation & Assembly

• General Instructions for Electricians (Switches & Dimmers)
• Junction Box Assembly Diagram (Rotary Dimmer)
• Invisible Plate Installation Notes
• Circuitry Visual Aid
• Home Automation Integration

Plates & Finishes

• Finish Swatches
• Custom Engraving
• Plate Cleaning Guidelines
• Sustainability Statement