📄 Selecting a Dimmer
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Selecting a Dimmer

Choosing the correct dimmer rating for your load is critical. Dimmer ratings are given in Amperes (A), so you must calculate the current draw of your load.

Usually, appliances specify their power consumption in either Watts (W) or Amperes (A).


Current-Based Calculation (Amperes)

Since AC current is sinusoidal, you cannot simply match the dimmer’s rated current with the load current. You must calculate the effective RMS current. If you


























are unsure how to do this, follow this simplified rule:

I(dimmer) ≥ I(load) × 0.77   or   I(dimmer) ≥ I(load) / 1.3

This 0.77 factor (1/1.3) provides a safety margin to account for inrush current and overload.

Reference:

  • 40A dimmer → max AC load: 31A

  • 24A dimmer → max AC load: 18.5A

  • 16A dimmer → max AC load: 12A

  • 10A dimmer → max AC load: 7.7A

  • 8A dimmer → max AC load: 6A

  • 4A dimmer → max AC load: 3A


Power-Based Calculation (Watts)

If your device specifies power in watts (P), use Ohm’s law: I = P / U

Where:

  • I is current in Amperes (A)

  • P is power in Watts (W)

  • U is voltage in Volts (V)

For 220V: I = P / 220

For 110V: I = P / 110

Example: 1100W load at 220V → I = 1100 / 220 = 5A

With a 30% safety margin: I × 1.3 = 6.5A → Choose an 8A dimmer

You can refer to a table below for the max power supported at 110/127V and 220/230V, based on different dimmer ratings and a 1.3 safety factor.

Dimmer
For 110/127V
220/230V
40A
max 3.4kWt
max 6.4kWt
24A
max 2kWt
max 4kWt
16A
max 1.3kWt
max 2.6kWt
10A
max 8.5kWt
max 1.7kWt
8A
max 0.7kWt
max 1.3kWt
4A
max 0.35kWt
max 0.66 kWt

* 1 kWt=1000W

Recommended Safety Margins

  • Resistive loads (incandescent bulbs, heaters): 30% margin

  • Inductive loads (some motor types): 50% margin

  • High inrush loads: up to 70% margin


Compatible Load Types

AC dimmers are suitable for the following types of loads:

  • Incandescent bulbs – Ideal resistive load for dimming

  • Dimmable LED bulbs – Designed to work with phase-cut dimmers

  • Gas-discharge lamps (halogen, neon) – Require a minimum voltage to start (typically 30–40% of nominal), limiting dimming range

  • Heating elements – Pure resistive loads, perfect for dimming

  • Electric boilers, heaters – Fully compatible

  • Instant water heaters – Must match the dimmer’s current rating

  • Electric kettles – Ensure power is within the dimmer’s limits

  • Fan heaters – Check minimum dimming level for fan operation

  • Oil-filled radiators

  • Underfloor heating – Electric mats or water pump control

  • Hairdryers and fans – Minimum dimming level of 40–50% is required

  • Water pumps – Requires RC snubber for protection

  • Other resistive devices – e.g., irons, toasters

  • Some electric motors – Require built-in or external RC snubbers

Not recommended with:

  • Non-dimmable LED bulbs – May flicker or fail

  • LED drivers – Most are incompatible with phase dimming

  • CFL bulbs – Incompatible internal electronics

  • SMPS and electronic power supplies – Risk of damage

  • Electronic current stabilizers – Conflict with dimmer operation

  • High-power inductive loads without protection – May produce voltage spikes