← Dimmers Guide | Contents | Next: Hardware Connection →

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.

Simplified Selection Rule

If you are unsure how to calculate the current, 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 Table

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)

Formulas by Voltage

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

Example Calculation

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.

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

← Dimmers Guide | Contents | Next: Hardware Connection →