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About this tool
Check whether the appliances on one extension board exceed its amp rating, the cord ampacity, the 80% continuous rule or safe voltage drop.
This checker adds up everything plugged into one extension board and converts it to amps with I = watts / (volts x power factor), then compares that current against the lower of two limits: the amp rating printed on the board and the ampacity of its flexible cord. It also applies the 80% continuous-load ceiling from NEC 210.19(A)(1) for anything running three hours or more, and estimates voltage drop from the two-way copper run so a long thin cord does not quietly cook itself. Use it before plugging a heater, kettle or air conditioner into a strip that was only ever meant for chargers and a lamp.
Open Extension Cord Load Checker on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Compares the load against the board rating AND the cord ampacity, whichever is lower.
Applies the 80% de-rating that governs anything running three hours or more.
Warns when a fridge or AC compressor start-up spike would exceed the board's rating.
About 1380 W at 230 V (6 A x 230 V), and only 1104 W if the load runs three hours or more, because the 80% continuous-load ceiling applies. That rules out a 2000 W heater or geyser on a 6 A strip entirely.
Only into a 16 A board on 1.5 mm² or thicker cord (or a 15 A / 14 AWG cord on 120 V), and never into a light-duty strip. A 2000 W heater draws 8.7 A at 230 V continuously, which is above the 4.8 A continuous ceiling of a 6 A board.
Thicker than you would use short, because voltage drop rises with length: keep the two-way drop under 3% of supply voltage. A 1000 W load on 120 V through 15 m of 16 AWG already drops about 2.7%, so beyond that go to 14 AWG or 12 AWG.
Heat means the current is at or above what the contacts and cord can carry — usually a high-wattage appliance, a coiled cord that cannot shed heat, or a daisy-chained second board. Unplug the largest appliance immediately and have an electrician inspect the strip and the wall socket before using it again.
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