Measuring Power Consumption Of 230VAC circuit?

[RalphVa]

Just so wrong. The current in each 230V line is the same. Even in the unlikely event of ain unbalanced load (current flow in the neutral), the current is the average of the two line currents, not the sum.

They both have to be the same to get the 240v. The white "neutral" will return both red and black lines.

What some of you don't understand is about the Kill-a-watt gizmo. I have a 120v one, too. It measures the actual kw-hr of usage over time. It's great for devices that go off and on over time, and you want to know how much they're actually running.

Just connect it across either the red or black line to white through a 120v plug. Plug the kill-a-watt gizmo into the 120v plug. Multiply your kw-hr by 2.

Ralph

 

[Chewwy]

That's the point!!
They might not be quite as bad as 10%, but you can't simply plug one in and expect real accuracy. About the only way to solve that issue is to measure the reading against a precision meter at low, mid, and high readings to develop an accurate scale. I have had similar experience with analog pressure and temperature sensors connected to a PLC. Those require the actual reading to be multiplied by a gain factor with an offset factor added in to get a correct reading.

One gets what they pay for. A Simpson analog VOM is around +/- 2% full scale, but it’s $300+. Can’t expect much accuracy for $25.

 

[npalen]

They both have to be the same to get the 240v. The white "neutral" will return both red and black lines.

What some of you don't understand is about the Kill-a-watt gizmo. I have a 120v one, too. It measures the actual kw-hr of usage over time. It's great for devices that go off and on over time, and you want to know how much they're actually running.

Just connect it across either the red or black line to white through a 120v plug. Plug the kill-a-watt gizmo into the 120v plug. Multiply your kw-hr by 2.

Ralph

Interesting! So, for us laymen, exactly how would the plug be connected? I'm guessing the neutral side of the plug would go to the neutral in the breaker box but not sure about the "hot" side of the plug.

Edit: After further thought, the hot side of the plug would simply piggyback to the red or black as you mention. This would be, I assume, how a 120VAC is normally wired off of a 240VAC. What I don't understand, though, is how the Kill-a-watt would sense the voltage and current in the red or black.

This would be in a sub panel so the neutral and ground are not bonded for what that's worth.
Edit: But they are bonded in the main panel of course.

 

[npalen]

One gets what they pay for. A Simpson analog VOM is around +/- 2% full scale, but it’s $300+. Can’t expect much accuracy for $25.

I have a Simpson analog VOM that you could have for $300. Works great but does have a lot of experience, however.

 

[Chewwy]

I have a Simpson analog VOM that you could have for $300. Works great but does have a lot of experience, however.

Thanks. I still have the one I bought in 1978. It only cost about $100 then.

 

[CobyRupert]

Just so wrong. The current in each 230V line is the same. Even in the unlikely event of ain unbalanced load (current flow in the neutral), the current is the average of the two line currents, not the sum.

The power is the sum of the two line currents times 120V.
The power is also the average of the two line currents times 240V.

You’re both right! “Kumbaya my lord...”

 

[Industrial Toys]

I have Simpsons that I would let go for $300.00 CDN!

 

[RalphVa]

Interesting! So, for us laymen, exactly how would the plug be connected? I'm guessing the neutral side of the plug would go to the neutral in the breaker box but not sure about the "hot" side of the plug.

Edit: After further thought, the hot side of the plug would simply piggyback to the red or black as you mention. This would be, I assume, how a 120VAC is normally wired off of a 240VAC. What I don't understand, though, is how the Kill-a-watt would sense the voltage and current in the red or black.

This would be in a sub panel so the neutral and ground are not bonded for what that's worth.
Edit: But they are bonded in the main panel of course.

Not sure exactly how you'd connect the Kill-a-watt. Think it actually has to be in the line carrying the current and cannot just sense it like a voltmeter.

Ralph

 

[npalen]

Not sure exactly how you'd connect the Kill-a-watt. Think it actually has to be in the line carrying the current and cannot just sense it like a voltmeter.

Ralph

Okay. I apparently misunderstood what you said in post #51 above.