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Forum Index : Electronics : Use of 3 phase meters for 3 ciruits instead?

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Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 83
Posted: 08:17am 19 Nov 2021
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Hope this is in right enough forum....and not too stupid a question.

Is there any reason 3 phase meters can not instead be used to measure 3 circuits off a single phase - that is feed the same phase in to all 3 phases and run 3 circuits off each "phase" for metering of each circuit? Not sure if sync or phase angle is a common measured parameter, if so rather than 120 degrees it would be 0!
Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.
 
phil99

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Joined: 11/02/2018
Location: Australia
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Posted: 11:17am 19 Nov 2021
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It depends on the model. Basic units are often just 3 volt meters and 3 ammeters in one package, so they should be ok. Others also measure frequency, power factor for each phase and phase sequence. They may also have alarm outputs for any / all the above when above / below limits. The manufactures data sheets should have the answer.
 
Davo99
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Joined: 03/06/2019
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Posted: 12:45pm 19 Nov 2021
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There are some pretty Cheap KWH meters On EAliGood.

I'd say the older the meter the better chance you have especially if it's an old Spinny Analogue type.

I have an old house power meter I use which is very handy for showing current direction when Playing with Induction generators so you know where the power is going and setting speeds etc.
 
phil99

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Posted: 11:18pm 19 Nov 2021
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"if it's an old Spinny Analogue type"

A single phase one is ideal for such things. I use one too, but a 3 phase one is unlikely to work properly on single phase as the disc is the rotor of a modified induction motor and the the phase differences matter.
 
Warpspeed
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Joined: 09/08/2007
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Posted: 01:42am 20 Nov 2021
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There is a good possibility this will work, but I cannot see what the advantage would be over using just a single wattmeter ?
Cheers,  Tony.
 
Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 83
Posted: 07:46am 20 Nov 2021
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  Warpspeed said  There is a good possibility this will work, but I cannot see what the advantage would be over using just a single watt meter ?


Will a single watt meter report on 3 circuits contemporaneously? Also some may be limited to 10 amps?  Of course 3 watt meters with adequate power capacity could be used. 3 mountings and likely larger form factor resulting.

There are 3 phase chint meters with RS-485 outputs which was what I was looking at.

I was contemplating logging three circuits all from the one phase, maybe with an arduino, if I can get a working interface.
Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.
 
Warpspeed
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Posted: 08:47am 20 Nov 2021
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A three phase wattmeter measures total power for all three phases combined, you don't get a separate power reading for each individual phase.

If you have a three phase circuit, and you are billing someone, all you want to know is TOTAL power used, and that is what you get.

If you want to log thee or more individual circuits you will need an individual wattmeter for each individual circuit.
Cheers,  Tony.
 
phil99

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Posted: 11:55am 20 Nov 2021
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The original post doesn't indicate what is to be measured. If it is energy then as Warpspeed says, a regular kW-Hour meter just gives the total. If it is power then a suitable electronic panel meter for a switchboard can be found. There are more types than you can poke a stick at.
 
Warpspeed
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Posted: 12:11am 21 Nov 2021
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My own three phase smart meter just indicates total Kwh for all three phases combined, and the direction of power flow.

The power utility could not care less what proportion of the total was drawn from each individual phase.
Cheers,  Tony.
 
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