Hello, I have purchased a Sensor Current Switch 100A, NPN part # CR9321-NPN. It was my understanding that when installed it would have a switch which in the open state when the circuit was energized and when the circuit was de-engized the switch would close.
I received and installed the CR9321-NPN, the circuit which this was installed on was 120VAC and the load was drawing 0.5 amps. The sensor current switch leads were open with the circuit both energized and de-energized.
I don’t know if I purchased an item thinking it would do something it is incapable of or if it is designed to perform as described above and is defective.
Your input is appreciated.
Greetings,
This sort of device uses the magnetic field generated by current flow to actuate a switching mechanism, with “on” typically translating into a contact closure. As such, it would appear that your statement of expected function may be reversed. Or just mis-typed…
Some amount of voltage drop across the device in its closed state will occur. Depending on the measurement technique used, that voltage drop may or may not prevent recognition of a “closed” state.
It could also be imagined that the power factor of the sensed current waveform may affect function of the sensor. Many electronic devices only slurp current near the peak of the AC waveform, and I’d not be surprised if the apparent amount of current required to actuate the switch would shift under those conditions.
Some additional information on how you’re testing the device would be useful, and note that the sensitivity of the device can be increased by looping the current-carrying conductor through the window multiple times.
Hello Rick,
Thank You for the prompt response. I am using a basic Fluke, T5-1000 “Electrical Tester” to check for continuity between the two leads on the CT. I am seeing an open switch with infinite ohms both with the CT energized and de-energized. When the circuit is energized the fan motor draws 0.5 amps.
I am a retired electrician; I have installed a lot of CT’s for power monitoring / consumption (I’ve never installed one to have a switching function to perform monitoring the circuit for being energized or the circuit being de-energized).
We have installed a radon mitigation system, the fan is in the inaccessible area of the attic. What I sought to do was to have a contact which would close on loss of power to the fan, this would be tied to our home’s alarm/security system. Should the fan motor fail and go into locked rotor or cease to function it would either trip the circuit breaker or cease to draw current - in either failure mode, the CT would sense the loss of power and the switch would close, the switch is tied to a wireless transmitter sending a signal back to our alarm panel. The CT is installed in the circuit breaker panel, on the 120VAC wire coming off the circuit breaker.
Should I be seeing the current sensor switch going from open when the circuit is energized to closed when de-energized?
Thank You very much
The device should provide a “switch closure” when current flow is detected.
Because it’s a solid-state “switch” however the resistance you’d measure across it depends A Lot on the test signal your instrument applies.
The specifications for your T5-1000 seem to indicate that it only measures up to 1000Ω.
It’s entirely possible that for small test currents the sensor would look like a higher resistance than that. It’s datasheet tells us to expect a 1.5V drop when conducting 120mA.
If the output is made from a bipolar transistor as the datasheet suggests, that figure might fall to only 1.2v or so when it’s only carrying 1mA. It’s “resistance” would then look like 1.2K and be out of your meter’s range, even though the sensor is operating normally.
I’d suggest trying again using a different meter that has a higher resistance measurement capability and/or a diode test function.
Hello Rick,
The current switch from DigiKey works, it does open and close.
I had a vintage Simpson 260 with leads still in the box.
The CR9321-NPN is closed when it senses current flow and opens on loss of power.
The current switch operation I would need, would have the opposite functions. Open when sensing current flow and the switch closes on loss of power. Would that be a CR9321-PNP?
I’m not sure that the alarm system component which would tie to the current switch has sufficient gitty up and go to drive the transistor, it only has a 3 volt battery.
Thank You Very Much,
Tom
To what wireless device are you trying to connect? Its specific requirements would inform possible solutions.
Most of the solutions that come to mind though would involve soldering together a small handful of components. The upside of that is that the sort of delayed-response you’re after should be relatively easy to achieve.
Hi Rick,
The alarm company stated that they would use the door side of a door alarm contact.
When the cover is removed here is what is inside:
In my communications with our security/alarm system provider they emailed me saying this is what they would use and the current switch is to go to the “closed” position when the system is to receive an alarm notification.
At my main electrical distribution panel is where the feed for the radon mitigation fan derives its power from. I was going to install the current switch on the wire coming off the circuit breaker, pop the two current switch leads out a 1/2" knock out on the side of the panel where they would mount the wireless switch transmitter.
What prompted me to investigate doing this sort of alarm system notification for the radon fan, is the fan is in an inaccessible location in our attic. Yesterday the radon mitigation system was installed, when they installed it they put in a means for me to see how much vacuum the fan is drawing in the basement, I was unaware that they were going to do this, so I do have a means of knowing that the system is working correctly.
For now I can sleep at night knowing the system is functioning correctly. I will let this all settle down and come back to it at a later date. If possible, I recontact you in the early spring of next year.
I sincerely appreciate all your thoughts and input, Thank You!
Wishing you a very Merry Christmas and a most pleasant New Year!
Tom