Hacker News Reader

Comment by cowsandmilk | Hacker News Reader

Considering the electric code has an 80% rule for loads, anyone assuming they can use 100% of what is on a label probably should not be doing electrical work.

View on HN

Which electrical code? They vary from country to country and even state/province in some countries!

I agree with you, but. The NEC has an 80% rule for continuous loads (over 3 hours) that use a typical circuit breaker as overcurrent protection. If you use fuses or a 100% rated breaker as your over current protection, then you can use all of the available ampacity. Anyways, devices that use a 15A receptacle (for example) will not draw more than 12A continuous if they’re meant to run continuously (3 hours or longer).

https://www.se.com/us/en/faqs/FA104355/

Very true. My computer says 240V on it, so I should only use it up to 192V.

Interestingly, the peak voltage of 240V AC (typical) is 330ish+ volts.

Typical house wiring is required to handle 600v due to voltage transients and wear and tear.

So any component rated to 240V dc will fail immediately on AC, and even 400-500V DC is not a good idea.

I guess there is a reason there is a whole category of engineers for this kind of thing.

No, you just shouldn't assume that that's the case. In the case of a computer and mains, both of those are nominal voltages and there will be a range of voltages which are expected to function, and if you want to check for sure, you should check those ranges.

The point is, voltages are usually a 1:1 match. That includes when you're working with ranges, you want the supply range to be inside the load range.

And even for amps where you see that 80% rule, that's for keeping the load smaller than the supply. Solar panels aren't a load and don't work that way.

Reply on news.ycombinator.com