Power strip outlet derate
Compare your light watts to a power strip’s amp rating after a continuous-load derate (often 80%).
allowed_W = strip_A × volts × (derate% ÷ 100) · headroom = allowed_W − light_W
When to use
This tool helps when you want a power strip outlet derate planning figure with the assumptions written down. You will enter power strip rating (amps), voltage (v), continuous derate (%), and total light / décor watts on the strip.
Compare your light watts to a power strip’s amp rating after a continuous-load derate (often 80%). Keep units consistent (feet vs inches, watts vs amps), then use the formula box to see how each term contributes.
Stop and ask a licensed electrician when loads, hardwired outlets, or roof work go beyond temporary plug-in holiday displays.
80% is a common planning target for multi-hour holiday loads.
Worked example
Example inputs from the form defaults — Power strip rating (amps) = 15; Voltage (V) = 120; Continuous derate (%) = 80; Total light / décor watts on the strip = 900 — are plausible homeowner figures, not a survey of your roofline.
Compute with: allowed_W = strip_A × volts × (derate% ÷ 100) · headroom = allowed_W − light_W. Show intermediates before the final count or cost.
When the calculator and scratch math disagree, fix units first; the power strip outlet derate model is only as good as consistent inputs.
Limits / assumptions
Units: keep every length in one system (feet or inches end-to-end) and every electrical quantity in the units the labels name. Mixing without converting invents a wrong answer.
Where the formula fails: odd roof geometry, wind on inflatables, worn sockets, and conditions not listed on the page are outside the model. Zero or nonsense inputs should error — do not force a number.
Not a substitute: the power strip outlet derate result is a planning aid. It is not an NEC determination, not a licensed electrician’s opinion, and not a manufacturer max-connect chart.
Not electrical advice. Follow the strip label, cord ratings, and local code. Do not daisy-chain power strips outdoors.
FAQ
Is derate the same as the breaker 80% rule?
Same idea — continuous loads heat plugs and cords; planning under ~80% of the strip rating is safer.
Strip says watts not amps?
Divide listed watts by voltage to get amps, or enter watts directly as light watts and set strip amps so strip×V matches the label.
Daisy-chaining strips?
Avoid stacking strips. Use this for one strip plugged into a wall or a rated outdoor cord.
GFCI trips?
Also check total circuit load with the GFI circuit headroom calculator.