Experimenting with 2 CTs in series

[yyzguy]

As an experiment I wired 2 50A CTs in series to monitor a 2 phase 220Vac unbalanced circuit.   I’ve compared the results to having 2 separate 50A CTs on each leg of the same circuit.

I did this with both my Dryer and my Air Conditioner.

With the 2 CTs wired in series, it’s necessary to “flip” one of the CTs in order for the phase to be correct.

It works pretty good.   The result from the series CTs don’t match exactly to that of a pair of CTs, but i think it’s close enough.   I’m not sure the expected error with any particular CT.   My results are less than 1% different, so I imagine that’s within any expected tolerance.

I’ve attached 2 screenshots of my Dryer’s amp draw.   One of the pictures shows the dryer with just the tumbler running, no heat.   In that case one of the legs of the 220v circuit shows zero amps, while the other shows the amps for the tumbler only.   The total is close, but not exact.   I show the dryer again, with both heat and tumbler running.

I’ve attached 2 other screenshot showing my Air Conditioner amp draw.   The air conditioner tends to be balanced.    Just as with the dryer, the two legs measured separately add to just about the same total as measured by 2 CTs connected in series.

[yyzguy]

Well, I spent about 30 minutes editing the previous post and adding additional information.   Apparently there’s a time limit before no more edits are allowed.

Hopefully there’s enough information that it makes sense.  Otherwise, if you have questions please post.   If it’s too confusing, I’ll start over with a new post.

 

 

[Peter]

The air conditioner is a straight 240 volt load, it does not use a neutral.

The dryer has 120 volt coxntrol and drum motor and 240 volt heater, and requires a neutral for the 120 volts. The series CT does not see the correct load for just 120 volt use

[Author]

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