Smart Switch Load Check Calculator

Compare a smart switch or relay module against a connected load using watts, amps, voltage, power factor, inrush multiplier, derating, and per-channel limits.

📌Real Load Presets

⚡Switch and Load Inputs

Circuit voltage (V)

Use nominal supply voltage: 120, 240, 24, or 12 V depending on the controlled circuit.

Total running load (watts)

Use steady nameplate or measured watts for every load controlled together.

Load class and power factor profile

The profile supplies power factor, typical inrush, and expected relay stress.

Inrush multiplier (x running amps)

LED drivers, motors, and transformers can draw several times running current at turn-on.

Switch total amp rating (A)

Use the rating for the load type when the datasheet lists separate lamp, motor, or resistive ratings.

Active output channels sharing load

For multi-channel relays, enter only the outputs that share the entered total load.

Per-channel amp rating (A)

Use the smaller channel rating if it differs from the total device rating.

Derating rule for steady load

Derating compares running amps against a safer long-duration capacity.

Switch Load Results

Running Current 0 A Watts divided by voltage and PF

Derated Capacity 0 A Safe steady switch limit

Channel Load 0 A Per active output channel

Inrush Check 0 A Peak turn-on current model

⚙Switch and Load Spec Comparison Grid

180 W Entered steady load before amp conversion.

120 V Circuit voltage used in watts-to-amps math.

0.90 PF Power factor profile for AC current estimate.

5 A Total switch amp rating before derating.

80% Selected steady-load derating multiplier.

5 A Per-output channel rating for shared loads.

8x Peak current multiplier applied at turn-on.

Check Overall status from steady, channel, and surge margins.

📊Reference Tables

Load Class	Power Factor Used	Typical Inrush Range	Why It Matters
LED driver or smart bulb group	0.85 to 0.95	6x to 10x running current	Low watts can still stress relay contacts when many drivers energize together.
Incandescent or halogen lighting	1.00	1.2x to 1.8x running current	Simple resistive math, but cold filaments create a brief turn-on bump.
Resistive heater or heat lamp	1.00	1x to 1.2x running current	Steady current and continuous-load derating are the main constraints.
Small AC fan motor	0.60 to 0.75	3x to 6x running current	Motor ratings and relay contact type matter more than watts alone.
Pump motor	0.80 to 0.90	5x to 7x running current	Locked-rotor and restart current can exceed a general lighting switch rating.
Low-voltage DC output	1.00	2x to 4x running current	Channel current rises quickly at 12 V or 24 V because voltage is low.

Switch or Relay Rating	Common Rated Load	Derated Continuous Load	Best Fit
5 A smart dimmer or small relay	600 W at 120 V resistive equivalent	4 A using an 80% rule	LED lighting groups and small non-motor loads within the lamp rating.
10 A smart wall switch	1,200 W at 120 V resistive equivalent	8 A using an 80% rule	General lighting, bathroom fans, and moderate mixed loads.
15 A plug-in module	1,800 W at 120 V resistive equivalent	12 A using an 80% rule	Appliance-style resistive loads where the module is rated for them.
16 A DIN relay module	3,840 W at 240 V resistive equivalent	12.8 A using an 80% rule	Panel-mounted control of larger resistive or properly rated motor loads.
2 A low-voltage channel	48 W at 24 V DC	1.6 A using an 80% rule	Small LED strips, valves, relays, and actuator outputs.

Running Watts	120 V at PF 1.00	120 V at PF 0.70	24 V DC at PF 1.00
60 W	0.50 A	0.71 A	2.50 A
120 W	1.00 A	1.43 A	5.00 A
300 W	2.50 A	3.57 A	12.50 A
600 W	5.00 A	7.14 A	25.00 A
1,500 W	12.50 A	17.86 A	62.50 A

Preset Scenario	Voltage and Load	Switch Rating	Primary Check
Kitchen LED cans	120 V, 180 W LED driver load	5 A lighting-rated dimmer	Low running current but high LED turn-on multiplier.
Bathroom fan	120 V, 85 W small motor	10 A wall switch	Power factor and motor inrush raise the amp check.
Plug-in heater	120 V, 1,500 W resistive load	15 A module	Continuous derating is the limiting factor.
Dual irrigation valves	24 V, 36 W transformer load	5 A per relay channel	Per-channel current is checked after channel splitting.
Small pool pump	240 V, 750 W pump motor	20 A motor-rated relay	Motor inrush margin is more important than steady watts.

✅Load Check Tips

Check the smallest rating. Compare running current against the derated total switch limit and the derated per-channel limit. A multi-channel relay can pass total amps while one output is overloaded.

Separate steady load from inrush. Watts-to-amps math checks heat during normal operation. LED drivers, transformers, and motors also need a peak turn-on check against the relay contact type.

This calculator is a planning check for load matching. Confirm the exact device datasheet, load category, enclosure temperature, protection device, and local electrical rules before using any smart switch or relay.

When you use a smart switch to turn on lights, the smart switch use a relay to provide electricity to the load. For the installation of a smart switch to be successful, you must match the electrical load that the smart switch is to be controlled by to the smart switch relay. Many people dont perform this critical task of matching the load to the relay, which can result in the smart switch failing early or the smart switch refusing to power the electrical fixture.

Comparing the number on the nameplate of the electrical load with the ratings on the smart switch is a simple step that you must perform to ensure that the smart switch will be able to handle the load. Each electrical load draw current in a different way. For example, LED drivers often have low wattage ratings, but draw several time that wattage when first switched on.

Match a Smart Switch to the Electrical Load

Exhaust fans often have low wattage ratings for there running loads, but the fans place stress on the relay due to their low power factor and long startup surge. Resistive heaters have a steady electrical current, and have a power factor that is near one, causing them to create heat within the smart switch. Relays are not rated for the wattage of the load, but for the different type of current that each type of load draws.

The calculator provided here can perform the mathematical calculations necesary to determine if the smart switch can handle the electrical load. After entering the voltage of the circuit, the total running watts of the load, the load class, and the switch ratings, the calculator will convert the running watts into running amps, using the power factor of the load class. The derating percentage that is entered will determine how many amps the relay can carry continuously.

Furthermore, the calculator will divide the total running amps by the number of active channels of the smart switch. Finally, the calculator will multiply the running current by the inrush factor to determine the peak of the inrush current, which you will compare with the switch ratings to ensure that the load match the smart switch. The power factor is a critical element to the calculations of whether a smart switch can handle an electrical load.

A load with a low power factor will draw more current than if it had a high power factor. The load class selector allow for the power factor to be selected appropriately for the load. Derating relays is important for ensuring that relays do not overheat.

For example, a relay that can carry 15 amps for short periods of time may overheat if it is required to carry 12 amps for long periods of time. The derating percentage allow for the smart switch to account for warm environments and long periods of operation. Furthermore, derating percentages that are set to a more conservative number than the switch specifications allow for the possibility that the switch will be installed in an insulated box.

Inrush current is another factor in the calculations. For example, if the inrush current of an appliance is too high, the relay contacts may weld together. You can enter the inrush current into the calculator and the calculator will model it to determine whether or not it will match the smart switch.

Each room typically has different type of electrical loads. For example, there may be both exhaust fans and LED lights. In this case, you can enter the total watts into the calculator along with the load class.

Furthermore, there are different load profile that can be tested in the calculator, and you can compare each load with the smart switch to determine if it can handle each type of load. Multi-channel relay modules allow for different channels to have their own on/off switches. You can divide the total amps drawn by the load by the number of active channels to determine whether the current of each channel is within the limit of that channel alone.

This prevents relay failure caused by each channel being near its limit. Temperature has an effect on the relay, but the calculator does not measure it. For example, relays may pass the calculations if they are in a cool environment in the house, but may overheat and fail if they are in a warm enclosure such as teh kitchen hood.

In this case, you can increase the derating percentage so as to allow the relay to dissipate more heat. The most common failure of a smart switch is due to the installer failing to account for the different specification of the switch. For example, the installer may fail to account for the impact of the power factor, the inrush current, and the individual limit of the channels within the smart switch.

Each of these specification are forced to be accounted for in the calculations that this calculator performs. The goal is for the smart switch to match to the electrical load so that the relay will last for a long time. By ensuring that the smart switch accounts for the running current, the per-channel current, and the inrush current, the relay will not fail.

Furthermore, by recognizing these common issue early in the installation process, you could of changed the smart switch and its components before the installation is complete.