Two light switches sit side by side on the trade counter. One is marked 10A, the other 10AX. They look alike, and a fitter asks the obvious question: what is the X for?

What the A and the X Each Promise

The clearest explanation comes from BEAMA, the trade body for the UK electrotechnical industry. Its May 2020 technical bulletin, Load ratings for manually operated functional switches, sets out what the letters mean on a switch marked to BS EN 60669-1.

• A means a maximum 10A tungsten or halogen load, and a maximum 10A inductive load with a power factor of 0.6.
• X means a maximum 10A externally ballasted lamp load. BEAMA's wording is rated current for externally ballasted LEDs and fluorescent luminaires.

So "10AX" is two promises written as one: the A load and the X load. The X does not add capacity. It adds a statement about a specific kind of lamp.

Why Lamp Type Needs Its Own Letter

A tungsten or halogen lamp is a simple resistive load. A fluorescent luminaire or an LED fitting with a separate driver is different: the ballast or driver sits between the switch and the lamp, and can draw a short, sharp surge at the moment of switching. That is a harder job for the contacts than a plain resistive load of the same current, which is why the standard gives the lamp type its own letter.

BEAMA also defines a self-ballasted lamp as a CFL or LED lamp where the control gear is built into the lamp, which is how most retrofit LED bulbs are made. The X is defined for externally ballasted lamps, so a 10AX mark does not by itself speak for every LED bulb on the shelf.

10AX Plate Switch or 20AX Grid Module?

The choice usually comes down to the system, not the rating alone.

• Plate switches come as a finished faceplate. BG Nexus Metal switches such as the black nickel NBN12 are listed at 10A 10AX 250V and need a 16mm metal box. The BG Nexus Metal Brushed Steel range has the same style in a brushed steel finish.
• Grid modules clip into a frame and plate you build yourself, which lets you mix 1-way, 2-way, intermediate, retractive and other modules in one plate. BG lists its grid switch modules at 20A 20AX, and the R13 intermediate module needs a 25mm minimum box depth. Browse them in the 20A 20AX grid modules collection.

If a grid plate needs a bell push or relay input, a momentary module is the right part, and our retractive switch guide explains how those work.

Mistakes That Cause Callbacks

• Reading 10AX as 10A of anything. The marking describes lamp loads. A motor, a heater or an appliance is judged against the equipment's own instructions and the switch's other ratings.
• Assuming 20AX is always double 10AX. BEAMA's dual-mark example shows 20A for one load type and 10A for another. Read the whole marking.
• Ignoring driver inrush. A single LED fitting is easy. Thirty on one switch needs the manufacturer's guidance.
• Forgetting box depth. Slim plate switches and grid modules need different depths, so check the product page before the first fix.