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.

Note

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

Simplified Selection Rule

If you are unsure how to calculate the current, follow this simplified rule:

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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 Table

Dimmer Rating	Max AC Load
40A dimmer	31A
24A dimmer	18.5A
16A dimmer	12A
10A dimmer	7.7A
8A dimmer	6A
4A dimmer	3A

Power-Based Calculation (Watts)

If your device specifies power in watts (P), use Ohm's law:

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I = P / U

Where:

I is current in Amperes (A)
P is power in Watts (W)
U is voltage in Volts (V)

Formulas by Voltage

For 220V: I = P / 220
For 110V: I = P / 110

Example Calculation

Example: 1100W load at 220V

Calculate current: I = 1100 / 220 = 5A
Apply 30% safety margin: I × 1.3 = 6.5A
Choose an 8A dimmer

Maximum Power by Voltage

You can refer to the 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	For 220/230V
40A	max 3.4 kW	max 6.4 kW
24A	max 2 kW	max 4 kW
16A	max 1.3 kW	max 2.6 kW
10A	max 0.85 kW	max 1.7 kW
8A	max 0.7 kW	max 1.3 kW
4A	max 0.35 kW	max 0.66 kW

Note: 1 kW = 1000W

Recommended Safety Margins

Different load types require different 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:

Fully Compatible Loads

Incandescent bulbs – Ideal resistive load for dimming
Dimmable LED bulbs – Designed to work with phase-cut dimmers
Heating elements – Pure resistive loads, perfect for dimming
Electric boilers, heaters – Fully compatible
Electric kettles – Ensure power is within the dimmer's limits
Oil-filled radiators – Standard resistive heating
Other resistive devices – e.g., irons, toasters

Compatible with Limitations

Gas-discharge lamps (halogen, neon) – Require a minimum voltage to start (typically 30-40% of nominal), limiting dimming range
Instant water heaters – Must match the dimmer's current rating
Fan heaters – Check minimum dimming level for fan operation (typically 40-50%)
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
Some electric motors – Require built-in or external RC snubbers

Not Recommended

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