# How should we tag questions that deal with power and data through the same cable?

Lots of people think it's better to have a single cable that carries both power and 2-way data to a device, rather than one cable for power and a second, separate cable for data. Do we already have a tag for that -- perhaps "powerline"? Should we make up a new tag -- perhaps "bias-tee" or "power+data" or "cable-reduction" or something else?

How should we tag questions related to that single-cable ideal? I'm tempted to tag them all with the "powerline" tag, but the phrase "powerline communication" often refers to the very specific idea of running data through the same 2 wires in the walls of a house used for mains power ( https://electronics.stackexchange.com/questions/tagged/line-power ).

I want a more general tag I can apply to systems where 2 wires carry combined data+power, where the power is supplied as DC power, or at least the power is much lower voltage than mains power. Systems such as model trains ( DC power line communications ), laser modulation ( I need to design a Bias-T circuit for a diode laser - help choosing component values ), coax cables that simultaneously carry power up to a pre-amp on the roof and TV signals from the pre-amp down to the TV (mentioned in Injecting a communication signal over DC power supply lines ), etc. Perhaps a tag "bias-tee" would be adequate for those kinds of systems.

However, even "bias-tee" refers to the specific configuration of an inductor and a capacitor to combine and separate the power and data. I suppose we could stretch it a bit and also apply it to things like analog telephone circuits that substitute a gyrator for the inductor.

I want an even more general tag I can use on questions about systems that may use techniques other than bias-tee to run power and data through the same cable -- such as the center-tapped transformer, used in some kinds of power-over-ethernet; or bundling 2 power conductors well-insulated from the 2 or more data conductors in the same cable, used in other kinds of power-over-ethernet.

That more general tag would be useful on questions such as " Safe Powering Methods - Working with Children " -- where the original poster just wants to send power and data through the same cable, and is willing to consider all of the above ways of doing that.

How should we tag questions that deal with power and data through the same cable?

• Is there any reason why the "modulation" tag is not good enough here? I guess you want a term that specifically means the power signal is the carrier? – Jon L May 25 '11 at 14:37
• Yes, I would like a term that specifically means "the power signal is the carrier" (as in the "1-wire bus"). I also want a more general term that means "power and data in the same cable", which includes "the power signal is the carrier", and also "modulation puts data at high frequency, and bias-T merges that modulated data with low-frequency power", and the center-tap PoE trick, and also "cables with lots of wires, where power is carried on a completely separate pair of wires from the baseband ("unmodulated") data wires" (something like USB or NMEA 2000). – davidcary Jun 11 '11 at 3:03
• I think you mean "wire" or "conductor" and not "cable". Multiconductor cables are extremely common. – Scott Seidman Oct 17 '13 at 21:26
• @ScottSeidman: Huh? If I really meant "wire" or "conductor" and not "cable" when I said "2 or more data conductors in the same cable" and "cables with lots of wires", what would that even mean? – davidcary Oct 18 '13 at 13:22
• Then I'm afraid I'm just missing the issue. Judging from the answers the issue is getting, most seem to be focusing on the issues of using the same conductors simultaneously for power and data. Can you give some more examples of QUESTIONS that would need this tag? Every RS232 cable, for example, carries power and data, but has absolutely noting to do with power line comm (selected as an answer below). It feels like you're combining two ideas that have little to do with each other. – Scott Seidman Oct 18 '13 at 13:36
• @ScottSeidman: According to Wikipedia: "RS-232", "No method is specified for sending power to a device." RS-232 was never intended to carry power. (Perhaps you are thinking of USB? or FireWire?). These "two ideas" you mentioned -- if we had two separate tags for them, rather than muddle them together as I proposed, what would you name those two tags? – davidcary Oct 19 '13 at 13:19
• Son of a gun, could have sworn there was a Vcc in there someplace, but was mistaken. As for the two tags, one would be powerline communication, the other doesn't need a tag – Scott Seidman Oct 19 '13 at 17:59

• @david: There's a wiki associated with each tag that can be used for clarifications like that. Also you can specify duplicate tags that should map to it, like power+data – endolith Apr 17 '11 at 19:41