There are regional differences that are probably causing some confusion. In the US, breakers have a nameplate rating 25% higher than their continuous load capacity. Go to Australia, for example, and the identical breaker will have a nameplate rating 80% of what it would in the US.

So you can run indefinitely at the nameplate rating in Australia, but only 3 hours in the US. And the startup current (inrush) can be much higher than the rating. Most breakers are thermo-magnetic. The magnetic part has a much higher tripping point and allows for inrush current. The thermo part trips when it gets too hot, and that'll be the current printed on the breaker.

No, continuous is very specifically defined in the NEC as 3 hours or more of runtime.

This article does a good job of explaining how failure modes/alternative usages can make that definition fuzzy: https://www.csemag.com/articles/understanding-overcurrent-pr...

Practically speaking, any intermittent device that _can_ run continuously or can fail to a continuous needs to be considered as such for safety purposes.

For example, a fridge should only run the compressor intermittently, but it has two obvious cases where the compressor could run indefinitely:

* An influx of heat, like filling an empty fridge with room temperature cans.

* A door being left open.

In the case of the kettle, it will likely be evaluated against it's "nominal" draw after the initial startup. If the auto-off sensor were to fail, it could run continuously at the tempurature.

I probably can’t speak to your jurisdiction, but no electrical inspector I’ve ever met would consider those loads continuous - in its precise, non-colloquial meaning - for the purpose of rating the circuit.

An appliance manufacturer may be under different UL regulations for failure modes of a device on a specific rated circuit. I don’t know anything about that.

[delayed]

If this is the standard then everything is a continuous load. A soldering iron or a hair dryer or a blender might get left on forever, who knows. Maybe I want the microwave to run 24 hours a day. If everything is a continuous load, why would the NEC make a difference at all?

Even in the context of your refrigerator example (which I don't necessarily agree with), a kettle should have two thermostats - a primary one that keeps the temperature setpoint, and a safety cutoff in case the primary stops working. In both fail and the kettle is somehow drawing its nominal power for hours at a time, the main safety hazard is going to be the kettle itself trying to dissipate >1Kw.