undefined | Better HN

0 pointsaaronmdjones4y ago0 comments

GP mentioned impedance, not resistance. You won't feel anything touching the 12/24V terminals in your car because they're DC. Your skin has a high resistance, but when faced with AC, has a low impedance. This makes AC much more dangerous, as you conduct 120V AC much better than 120V DC.

Even 50mA will likely kill you, as outlined on the "death graph" as we electricians call it. This is independent of voltage.

https://upload.wikimedia.org/wikipedia/commons/7/7f/IEC_TS_6...

Blue is harmless and imperceptible, green is harmless, yellow is harmful, red is fibrillation.

Edit: This illustrates why 30mA (or less) RCD protection is common (and required) in various jurisdictions, depending on the kind of circuits you're serving.

0 comments

3 comments · 2 top-level

jhgb4y ago· 1 in thread

> This makes AC much more dangerous, as you conduct 120V AC much better than 120V DC.

But at higher frequencies, you should experience the skin effect, right?

aaronmdjonesOP4y ago

I can't answer that question, as I'm only an electrician, not an electrical or RF engineer.

That said, we're referring to power delivery here, and the highest frequency I'm aware of in this space is the 400 Hz power distribution systems used on warships.

Reason0774y ago

Right, and in particular, "Type B" RCD protection is required for solar inverters in various jurisdictions. These provide protection against DC fault currents.

j / k navigate · click thread line to collapse