Why do we still deal with 60 cycle hum?

[lowfreqgeek]

I'm late to the party, but physics doesn't change. I don't know why that's so hard to understand.

 

[bucephylus]

No they don't, not at the typical 12V battery level. The human body's impedance is too high for there to be the 15mA or so needed to cause cardiac issues. I'm an EE and have worked in enough fields with gear that can kill you that 120VDC / 50VAC is potentially enough to kill you and where specific measures need to be applied to prevent it.

Great.

My first job out of undergrad was a Field EE for Bechtel at a two unit nuc plant under construction. The only deaths that occurred on the job site were electricians contacting 12 - 20 VDC circuits in the MCC’s. Other more spectacular events included one instance of a crane operator tangling into the 500 keV high lines; current arcing from the wheels; operator made smart decision not to jump. Also, Civils dumping water down an electrical conduit into the high side of a Load Center - 4.16 keV. Lots of fun.

A car battery is capable of delivering WAAAY more current flow than a household circuit. WAAY more than 15 mA. Current kills.

 

[bucephylus]

I'm late to the party, but physics doesn't change. I don't know why that's so hard to understand.

Thanks for the lecture.

You may or may not recall that the Scientific Method involves DISPROVING ideas. Good scientists do NOT prove ideas.

 

[crazycloud]

A car battery is capable of delivering WAAAY more current flow than a household circuit.

Yes, but not into a typical human body. Not my earlier comment about impedance of the human body - (IEC60749 was what we used - happy for you to show why this international standard is incorrect), and apply Ohm's Law. I also worked in power distribution for many years, until quite recently and the 120/50 rule was applied in all areas where we worked.

 

[bucephylus]

Yes, but not into a typical human body. Not my earlier comment about impedance of the human body - (IEC60749 was what we used - happy for you to show why this international standard is incorrect), and apply Ohm's Law. I also worked in power distribution for many years, until quite recently and the 120/50 rule was applied in all areas where we worked.

I’ll make sure to explain that to the two dead electricians when my days are finished. BTW, what exactly is the current path for the theoretical body impedance? From one hand to your foot? What happens when that same potential is applied across one hand? Etc.

Edit: OK, perhaps the car battery was a poor example. Still, the difference between DC and AC exposures is significant. I could equally say that the few times I’ve crossed up on 120vac has been not especially significant. And, the two deaths I described were experienced electricians contacting circuits at the site that they were unaware of. They were probably 50A - 60A circuits. Those are my data points.

 

[Hawk256]

DC voltage potentials drive much more current through you, when you complete the circuit.

You couldn't be more wrong as I see has already been explained to you.

 

[bucephylus]

You couldn't be more wrong as I see has already been explained to you.

Please feel free to elaborate. Specifically, which part? About the deaths at the job site I worked? About impedance of the human body?

BTW, while you are at it, what is the relevance of this “electrocution” discussion to 60 Hz pickup noise? Just curious.

On the topic of impedance of the human body, you do realize that impedance is complex, primarily capacitive; and that electrocution is actually a complex breakdown behavior; point being, it’s not a simple Ohms Law calculation. But, by all means your informed opinion is appreciated.

 

[Turnaround]

Slower frequency kan kill you, just slower.

Duh!

Yah - it takes one-tenth of a second longer at 50 Hz.