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Old 03-14-2009, 07:39 PM   #1
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What does split core mean?

I want to get a data logger (a device you attach sensors into and it takes measurements every x minutes which you later download to your computer so you can graph the data). One thing I want to track is my electric water heater element (a Rheem model 82V120HE-1) which the manual describes the electric data as

"Heaters furnished with standard 240 volt AC, single phase non-simultaneous wiring and 4500 watt heating element." and it's on a 30 amp breaker.

Will the sensor below be able to measure when my tank draws amps (the sensor is an Onset CTV-B, the data logger an Onset U12-006) it's described as

"A split-core AC current sensor responsive over the range of 0 to 50 amps AC for use with U12 data loggers with external input channels. With an input current of AC current, sine wave, single phase 50 Hz or 60 Hz, load power factor 0.5 to 1.0 lead or lag."

It's looking like it will, except I have no idea what split core means. Thanks


Last edited by Piedmont; 03-14-2009 at 08:01 PM.
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Old 03-14-2009, 08:08 PM   #2
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Split core means the CT's (current transformers) are not solid around so you do not have to remove the wire to install them. You can open the CT's to get them around the wire. Just like the laws of an Amprobe meter.

The jaws of an Amprobe are a current transformer. They are a "split-core" CT because you can open them to get them around the wire.
The inner steel ring of the jaws is the core.


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Old 03-14-2009, 10:10 PM   #3
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A word of caution about current transformers (CTs). CTs are just like any other transformer, they have a primary and a secondary. The primary is the wire that goes through the hole in the middle. The secondary is the two small wires that go to the meter or transducer.

NEVER, even for an instant, have current running through the primary of a CT with the secondary leads disconnected.

It doesn't matter if it's split-core, solid-core, bus-core, or anything else.

The first thing to do with any CT is to insure that the secondary leads are connected. If they're not, and current is running through the primary of the CT, VERY high voltage (over 3000 volts) will be present at the secondary terminals. For maybe a second. Then no voltage at all, because the CT has shorted out inside.

The first thing I test when troubleshooting power metering equipment is the CTs. 90% of the time, they're burned up. Almost always because the installer (or someone working on the system) didn't know to never open-circuit the CT secondary.


P.S. Your datalogger will work on your water heater circuit. It is indeed AC (not DC), single phase, sinewave (as opposed to a distorted waveform, like from an inverter), 18.75 amps (less than the 50 amp capacity of the CTs), and since it's a resistive load (as opposed to an inductive load, like a motor), the power factor will be 1.0
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Old 03-14-2009, 10:19 PM   #4
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... Deleted.... my question was answered. Thanks Micromind!
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