I want to subtract the power consumption of specific circuits from the overall power consumption

[victor.cherkashi]

Hello guys,

I have a panel with 42 circuits. Power meter is installed on the panels feeder.
I want to subtract the power consumption of specific circuits from the overall power consumption measured by the meter with current transformers (CTs) that is connected to the entire electrical panel.

Can I do it by wiring back those circuits thru the same current transformers? Order of phases to be maintained.

 

[__dan]

It looks like you're suggesting routing the load side wires back in reverse direction through the mains "CT's". That might work. You would have to experiment and independently meter the loads so you can confirm those magnetic fields do cancel (inside the mains ct's).

The CT's themselves have pulse train outputs usually on modern units to make them safe. They're not a CT externally.

But if you're inside the same mains doughnut where it's a CT internally, you may be able to cancel select loads by going back through in reverse direction. You would have to try it to see if you get the results you want.

 

[petersonra]

It should work. But you might want to test to make sure it really is if it is something that needs to be right.

 

[LarryFine]

Would this be worthy of adding a second panel?

 

[herding_cats]

There are a few ways to do this:

1. Leave the CTs where they are. Shut off all breakers except the one you want to data log.

2. Move the CTs to the individual circuit and then data log there, then moving the CTs around to other circuits.

3. There are some companies out there that build a data logger that has multiple CTs, as you could purchase a new data logger like this with 42 channels for example. Solar companies use them a lot to analyze power for homes, but it's all single-phase power. If I remember right I think the manufacturer on one of them was "In-Ocean" or something like that.

I wouldn't run the wires back through the CTs though for accuracy. FYI A lot of CTs are uni-directional if you try it to see if it works. If you run the wire backwards you will get bizarre readings.

 

[jaggedben]

...

Can I do it by wiring back those circuits thru the same current transformers? Order of phases to be maintained.

Yes.

 

[jaggedben]

It looks like you're suggesting routing the load side wires back in reverse direction through the mains "CT's". That might work. You would have to experiment and independently meter the loads so you can confirm those magnetic fields do cancel (inside the mains ct's).
...

How would they not cancel? Unless scientific precision is needed they will cancel closely enough.

 

[herding_cats]

It would read but just be aware you have doubled the loop. Total readings are 2x of actual power if that makes sense. It's being read twice.

 

[jaggedben]

... FYI A lot of CTs are uni-directional if you try it to see if it works. ....

A current transformer itself is completely bi-directional. (How do you think they handle alternating current?) Any 'CT' that is 'unidirectional' must either contain more actual components than just a CT, or else be hooked up to a meter that isn't programmed to take advantage of its bidirectionality.

 

[jaggedben]

It would read but just be aware you have doubled the loop. Total readings are 2x of actual power if that makes sense. It's being read twice.

Not if you run the branch circuit through in the opposite direction.

 

[jaggedben]

Yes.

Just pay attention to the direction the wires pass through the CTs.

 

[victor.cherkashi]

It would read but just be aware you have doubled the loop. Total readings are 2x of actual power if that makes sense. It's being read twice.

Today, I had a conversation with the metering company "utiliVisor." They mentioned that the sub-meter they usually supply is the CENTRON Polyphase (V&I) has no issues with that. According to them, circuits in the current transformer running in reverse will be subtracted from the total consumption of the panel.