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Author Topic: Power Monitoring of Inductive Appliances - How do you do it?  (Read 3756 times)

Offline maj34

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Just wondering if anyone here is using the popular Aeon Labs DSC06106-ZWUS (image attached) to measure power usage of inductive loads such as:
  • Air Conditioners
  • Fans
  • A refrigerator
  • A washer
  • Or anything else that has a motor

As you may or may not be aware - you should not do this as the device is only rated for resistive loads.  And this is the case for most of the Z-Wave switches I've seen.  Even those that are sold as "Appliance Switches" are not rated for inductive loads; this is unfortunate and a little deceiving since most appliances are inductive in nature.  For example, if you look up this device right now on Amazon it shows that it can be used to monitor a washer (and it says this text is "From the Manfacturer"!!).  But it's the rating label of the device (as approved by NEC/CSA/UL, etc) that's important. 

Go ahead - try to name a 15A appliance that is resistive (other than a heater)?  There probably are a couple, but the majority will not be pure resistive.

Apologies if this opens a can of worms (or a can of worry) for some people.

So is it safe?  Officially, no - it's not.  Each country has an electrical code (NEC in USA, CSA here in Canada) that specifies rules and using this device for any of the above purposes violates that rule.  It's a misuse of a device, and right there in the manual for the device it says Aeon Labs is not liable for damages, etc, due to a misuse.  I agree with them on this one, although I do think they suggest that this is safe for inductive loads by calling it an "appliance switch and monitor".

So is it safe - unofficially? Maybe for energy monitoring only.  In my opinion, the reason this device is rated for resistive loads only, is because its relay is not rated to interrupt inductive load current.  This type of current, by its nature, will cause a small arc across a set of contacts should the contacts open.  Eventually this may ruin the device and may have other safety implications.  However, if the device is always ON (which is how you may use for an AC or a refrigerator, the contact will always be engaged and there will be no arc.

Disclaimer: This is a theory only.  I cannot comment on why such a device is not officially approved for inductive loads.  You should always use devices as designated by their manufacturers recommendations (and by NEC/CSA approvals, etc). 

All of that said, is anyone out there using these devices for energy monitoring of AC units or other motor-based appliances?  Personally I'm thinking I might use it anyway (as described above as an energy monitor).  Would just like to know if other people have or have not had any issues with using it this way...

Offline Tony G

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Re: Power Monitoring of Inductive Appliances - How do you do it?
« Reply #1 on: May 23, 2013, 01:22:22 am »
Hmm... you raise a good point.  I was thinking of getting one of the Aeon Labs Aeotec DSC18103-ZWUS micro smart energy switches.  The manual http://www.homeseer.com/pdfs/Aeon%20Labs/AL_SES_G2_Manual_V15.pdf lists the following specs:

? USA: 120V 60Hz input, 1200W or 10A max output.
? EU/AU/IN/BR/CN: 230V 50Hz input, 2300W or 10A max output

with no mention of resistive or inductive loads.  Although the image  of the actual unit (attached) says use with resistive loads! 

How confusing.

Is anyone else using these with appliances? I also would like to use this with different appliances, such as televisions, water coolers, refridgerator, etc.  Failure rates? /Tony
« Last Edit: May 23, 2013, 01:24:31 am by Tony G »
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Offline akbooer

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Re: Power Monitoring of Inductive Appliances - How do you do it?
« Reply #2 on: May 23, 2013, 02:26:20 am »
Aside from the safety/lifetime issues you raise, I have been wondering about the accuracy of the measurement in such situations.  I'm rather assuming that these devices measure VA (volt amps), that is just the scalar product of the two, rather than real Watts which takes into account the phase angle in the case of inductive (or capacitive) loads.

I monitor my house power consumption with both clamp-on sensors and a data logger connected to the utility meter (which I take to be accurate!).  The clamp-on measurement is very considerably higher (like twice) for low whole house consumption in a faily quiescent state - a situation I believe to be due to a significant number of inductive loads (phone chargers, transformers for various appliances ...)
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Offline oTi@

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Re: Power Monitoring of Inductive Appliances - How do you do it?
« Reply #3 on: May 23, 2013, 08:48:17 am »
A/V, HVAC, fridge, computer gear, garage door; for energy measurement only; some on micro smart switch, some on smart switch.

FWIW, this is on the Aeotec 'lighting compatibility / fluorescent lighting' web page:
Quote from: http://aeotec.com/support/163-z-wave-lighting-compatible.html
The switching products will work with fluorescent lights, as well as large appliances, that draw up to a 5 amp current. Such devices specifically have a dash current. Where the load is ohmic the switches are compatible up to 10 amps.

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