Uni-directional clamp meter

[plugwash]

I think it is particularly easy to understand if one considers the simple situation when PF=1 (i.e. no reactive components). AFAICS, in that situation, and in direct analogy with the even simpler situation with DC, current and voltage will be in-phase for energy flow in one direction or 180° out-of-phase if it is moving in the other direction

Right.

Indeed so, and in the context of electrical energy (and electrical power), the established convention is surely that 'consumption' refers to conversion into some form other than electrical? Do you not talk about electrical heaters/appliances/whatever 'consuming energy'?

Right.

Similarly we think of devices that convert "some other form of energy" to electricity as "producing" power.

Is it not then reasonable to view production of power as "negative consumption" (or equivilently consumption of power as "negative production")

 

[JohnW2]

I think it is particularly easy to understand if one considers the simple situation when PF=1 (i.e. no reactive components). AFAICS, in that situation, and in direct analogy with the even simpler situation with DC, current and voltage will be in-phase for energy flow in one direction or 180° out-of-phase if it is moving in the other direction

Right.

I'm glad that we are agreed

Indeed so, and in the context of electrical energy (and electrical power), the established convention is surely that 'consumption' refers to conversion into some form other than electrical? Do you not talk about electrical heaters/appliances/whatever 'consuming energy'?

Right.

Goodness, again

Similarly we think of devices that convert "some other form of energy" to electricity as "producing" power. ... Is it not then reasonable to view production of power as "negative consumption" (or equivilently consumption of power as "negative production")

I think you're now getting more into 'colloquial language' - and (perhaps pedantically) sticking to the physics definition of 'power' as a rate, I'm not very comfortable with negative/positive power production/consumption (what would 'consumption' or 'production' of a rate actually mean?). Change the word to 'energy' and my comfort would return! ... although we are agreed that, strictly speaking, energy can (under normal circumstances!) neither be created not destroyed, I think we are also agreed that, in the context of electricity, 'production'/ 'consumption' relates to the conversion of non-electrical energy to electrical energy, or vice versa, respectively.

Kind Regards, John

 

[eveares]

It would detect the so called "direction" of the AC current the same way a non contact voltage tester can tell the difference between a line conductor and a non line conductor such as neutral.

You would get substantial capacitive coupling with the clamp on the line wire, but not on the neutral wire as neutral is usually at a potential of 0 to a few volts against the line conductor when the circuit is complete.

In other words there is a potential difference of around 230 volts between the line conductor and the neutral conductor.

 

[JohnW2]

It would detect the so called "direction" of the AC current the same way a non contact voltage tester can tell the difference between a line conductor and a non line conductor such as neutral. ... You would get substantial capacitive coupling with the clamp on the line wire, but not on the neutral wire ...

I don't really understand that.

... as neutral is usually at a potential of 0 to a few volts against the line conductor when the circuit is complete. ... In other words there is a potential difference of around 230 volts between the line conductor and the neutral conductor.

... and that I understand even less ... you seem to be saying both that L-N difference is "0 to a few volts" and that it is "around 230V". (my money is on the latter ).

Can you un-confuse me?

Kind Regards, John

 

[eveares]

There is usually a potential difference of around 230 volts between the Line and Neutral conductors.

neutral is usually at a potential of 0 to a few volts against the line conductor

When I say against, I mean neutral is at 0v and line is at 230v. In other words I was using the word against in the sense of comparison of the line and neutral voltages to each other.

I don't really understand that.

While it is true that AC does not have a true direction as it is alternating both ways, but I think you can easily understand that the device can identify the line conductor by the voltage induced in the sensor through capacitive coupling.

See here for information on capacitive coupling: http://www.testequipmentdepot.com/a...derstanding-capacitive-voltage-sensors_an.PDF

 

[JohnW2]

While it is true that AC does not have a true direction as it is alternating both ways ...

As you should see if you read all of this discussion, although the current flow obviously 'alternates' in direction, flow of energy does have a direction, even with AC - and that direction will be manifested by the phase relationship between voltage and current.

...but I think you can easily understand that the device can identify the line conductor by the voltage induced in the sensor through capacitive coupling.

I really can't see what that has got to do with the above, or to any of the discussion in this thread. Whatever, the reason why a non-contact tester detects the line conductor, by capacitive coupling, is because line voltage is high relative to earth, whereas neutral voltage is close to earth potential (being connected to earth at the substation).

Kind Regards, John