What BAD THING happens when you combine different voltages on one wire?

[Sparky]

Laying out a few scenarios. For the sake of simplifying discussion, assume

1) the wires used are sufficient to carry the HIGH SOURCE AND THE LOW SOURCE combined, however, in cases where Really Bad Things happen, these are not impervious to melting or exploding.

2) IN cases using DC ONLY, polarity is observed.

HIGH SOURCE = the high voltage applied

LOW SOURCE = the low voltage

Case 1: 120v AC + 120v DC(same number of watts, each source)

Case 1b: 120v AC + 120v DC (differing
number of watts, each source)

Case 2: 12v DC + 36 VDC (same number of watts, each source)

Case 2B: 12v DC + 36 VDC (differing
number of watts, each source)

Case 3:120v AC + 12v DC (Same number of watts, each source)

Case 3b:120v AC + 12v DC (differing number of watts, each source)

 

[Sparky]

I assume in each case there will be varying levels of smoke escapage on appliances used for load, but are there any cases where a person can decouple the contrasting voltages, or somehow use them? Could they drive a stove burner for instance?

 

[gnubie]

What's the purpose? In various industries it is not at all unusual to combine DC, AC and signalling on single wires but it is very application specific.

In days past TV studio cameras would have triaxial cable with an outer shield common / neutral, a next layer DC pilot conductor and finally a central conductor that carried DC, 50/60Hz 300V-ish main power, and higher up in frequency audio for the operator, video feeds and all sorts of things.

 

[Sparky]

The purpose? Idk. Signaling is one case, as you suggested for TV cameras. For a while (maybe still, idk) it was stylish to run ethernet using modified house plugs over 120v wiring.


Idk about other uses. Seems in the signaling scenario, one could separate the applied voltage again, so could one separate different power supplies & loads?

This is a thought experiment from a bored person, not much more ?

 

[gnubie]

EoP is pretty common still.

 

[HaldorEE]

Laying out a few scenarios. For the sake of simplifying discussion, assume

1) the wires used are sufficient to carry the HIGH SOURCE AND THE LOW SOURCE combined, however, in cases where Really Bad Things happen, these are not impervious to melting or exploding.

2) IN cases using DC ONLY, polarity is observed.

HIGH SOURCE = the high voltage applied

LOW SOURCE = the low voltage

Case 1: 120v AC + 120v DC(same number of watts, each source)

Case 1b: 120v AC + 120v DC (differing
number of watts, each source)

Case 2: 12v DC + 36 VDC (same number of watts, each source)

Case 2B: 12v DC + 36 VDC (differing
number of watts, each source)

Case 3:120v AC + 12v DC (Same number of watts, each source)

Case 3b:120v AC + 12v DC (differing number of watts, each source)

The term RMS is used to equate the heating effect of AC current to DC current.

120VAC is actually a constantly changing voltage going from -200V to +200V. If you pass 100W RMS (actually no reason to say RMS since this is implied by using the term W when referring to AC) through a resistive element it should get just as hot as passing 100W of DC through the same resistive element would.

Note: Putting DC together with AC on the same wires will work as long as you filter out the AC from whatever is using the DC. However, passing DC current through your transformer windings will heat them up, potentially causing them to fail.

 

[HaldorEE]

Studio condenser microphones use what is called phantom power. This is a low current DC voltage that is induced onto the audio signal. This is example of exactly what you are talking about. If your current needs are low and you have center tapped transformers at each end it can work well.

https://www.sweetwater.com/sweetcare/articles/what-phantom-power-need/

 

[Sparky]

Thanks for the responses. NGL, I was hoping for a little more catastrophe. Like dogs & cats living together, goldfish howling at the moon, mass hysteria type events to take my mind off covid. But your responses have been very informative.

 

[HaldorEE]

Thanks for the responses. NGL, I was hoping for a little more catastrophe. Like dogs & cats living together, goldfish howling at the moon, mass hysteria type events to take my mind off covid. But your responses have been very informative.

Well, as long as the AC is not oscillating at 432 Hz. Everybody knows about the power of 432 Hz.