Voltage Reference

[CaptainCanuck]

Hi everybody, newbie here. I've been doing some reading trying to get a better understanding of AC power, 3 phase, neutral vs hot vs ground, etc., etc. My question is simple. When the term "referenced to" is used, as in (something/some entity) is "referenced to ground", does that mean that it is physically connected to an object or conductor that is at the reference potential, in this case an object or conductor at ground potential? In other words, could you substitute "referenced to" with "connected to"?

- Cap'n C

 

[(*steve*)]

No.

If you're talking about a car battery you might say that the positive terminal is at 12V referenced to the negative terminal.

You definitely don't want to connect them together.

Voltage readings are always relative to some reference point. The wording you're asking about is just telling you what the village is referenced to.

It's a bit like saying that the top of my head is at 1.87 meters referenced to the bottom of my feet.

 

[davenn]

My question is simple. When the term "referenced to" is used, as in (something/some entity) is "referenced to ground", does that mean that it is physically connected to an object or conductor that is at the reference potential, in this case an object or conductor at ground potential?

not quite

In other words, could you substitute "referenced to" with "connected to"?

NO, definitely not

It means where you are measuring the voltages between ... where the 2 probes of the voltmeter are connected to
lets take your 3 phase example

you could be measuring the voltage between any 2 phases or between one phase and ground or neutral


in a DC circuit, you would be normally placing your negative meter lead on the 0V/negative rail in the case of a single rail power supply
and you would be doing measurements throughout the circuit referencing to that 0V rail

take this part of a circuit .....





I have circled the expected voltages ... as referenced to that solid black 0V rail
negative probe of voltmeter on the 0V rail and the positive probe to those measurement points

hope that helps


Dave

 

[davenn]

I was busy doing my cct when steve answered

 

[CaptainCanuck]

I should have been more clear and I should have linked to the passage I was referring to, and sure enough now I can't find it. I get all that about voltage references (and I appreciate the responses, as a newbie a review is always helpful), but in this case the writer used it as a verb, as in "I took this <physical entity I can't remember, probably conductor of some kind> and referenced it to ground". So my question was in that context. If I come across the example I'll post it.

 

[CaptainCanuck]

OK, I found the passage that prompted my question (among other examples). My memory didn't serve me perfectly well, but I was close enough. The discussion is here :http://forums.mikeholt.com/showthread.php?t=172607
The passage is: "The reason the neutral is the groundED conductor, is that it is bonded to the equipment grounding system/grounding electrode system at exclusively one point, where it gets a voltage reference to ground." To me the implication is that the conductor he refers to has a "voltage reference to ground" necessarily by virtue of of the fact that it has a physical connection to ground and I wanted to confirm that the term "voltage reference" can be used to imply a physical connection as in this case in addition to it being used in the way you do above in the context of measuring potential between to points.

 

[(*steve*)]

I agree with your reading of that phrase in that context, but only because of what I consider to be very poor wording.

If something is connected to ground it (ideally) has no (zero) voltage with respect to ground.

I'm actually unsure of what the writer means by using that phrase. Perhaps they mean that this point becomes the reference point for other voltages, and they can also be referenced to ground.

It is important to understand that in systems where neutral is bonded to earth/ground at some point, that the neutral potential often differs from ground potential. This happens because neutral currents cause a voltage drop in the neutral conductor. Unless there is a fault current the ground potential remains at the same potential throughout the system. In a well managed multi phase environment, neutral currents are minimised and this difference is ideally small.

 

[davenn]

The passage is: "The reason the neutral is the groundED conductor, is that it is bonded to the equipment grounding system/grounding electrode system at exclusively one point, where it gets a voltage reference to ground." To me the implication is that the conductor he refers to has a "voltage reference to ground" necessarily by virtue of of the fact that it has a physical connection to ground and I wanted to confirm that the term "voltage reference" can be used to imply a physical connection as in this case in addition to it being used in the way you do above in the context of measuring potential between to points.

in a home electrical system and many other cases. The neutral is bonded to earth at the fuse/meter box