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[dhouston]

When the Kill-A-Watt meter first came out, I bought one (for about $65 IIRC) and reviewed it very favorably on the Usenet comp.home.automation group (which still existed back then). The company that makes them (or their US dealer, I don't recall which) answered all of my technical questions. It proved to be highly successful with the price falling quickly to $35 or so and was available at corner drugstores (which still existed back then). Among other things I used it to measure the phantom power use of X10 modules. (Scroll down in the following link.)
https://www.laser.com/dhouston/x10-sig.html
Now, it sells for about $20 and has even made it into a story about phantom power in the NYT.
http://www.nytimes.com/2016/05/08/science/just-how-much-power-do-your-electronics-use-when-they-are-off.html?ref=technology

I do suspect the NYT reporter is too young to remember that dumb appliances of an earlier era used far more power than today's smart replacements. For example, my 52" smart TV draws 65W maximum which is about what the average incandescent light bulb (which still existed back then) used.

[Tuicemen]

I picked up one of these units when I first started adding solar to my off grid place.
I would have loved to have gotten it for your price instead I payed double that! (loony dollars)
Still it was and still is a valuable tool for finding Phantom loads and total power consumption of any pluggable electronic device.

[JeffVolp]

It is also interesting to compare the VA and watts readings.  VA measures the heating stress to electrical conductors and inductors in X10 filters, and watts measures energy actually consumed.  For low power-factor devices, the VA reading can be several times higher than the actual watts consumed.  That can cause a lot more heating in an X10 filter than the power consumption would lead one to expect.

Jeff

[bkenobi]

Not having much of an electrical background, that's interesting but meaningless to me.  The takeaway I assume is that if I want to use a 5A filter and have a bunch of small loads, then a <5A total load might actually be too much for that filter.  Correct?

[Brian H]

Depends on the loads.
If they where things like incandescent loads. You could probably just add the current up.
Pushing an XPPF close to 5 amps even with incandescent loads can over heat them.

Devices like some dimmable LED bulbs. Can have Inrush and Repetitive  current much higher than their ratings.
I have a few 8.5 watt dimmable LEDs and the manufacturer says count each one as 80 watts when determining a load on a dimmer. Those peek currents can also heat up the coils in an XPPF filter.

We had a user here measure the current into their fluorescent fixtures with a typical meter and measured below the 5 amp rating for an XPPF. The XPPF overheated and melted.

[JeffVolp]

Power consumption of most electrical devices is specified in watts, not amps.  We calculate the amps from I = P/V, but that only works when the power factor is 1.0, with VA and watts being the same.  For low power factor devices, the current can be significantly higher than the calculation would show, but that additional current is "imaginary", being out of phase with the applied AC waveform.  So while it causes heating in the wires (and X10 filters), it does not result in any additional power consumption.

For example, the XTB-ANR uses a 1.8uF capacitor across the powerline to act as a super signal sucker to attenuate noise.  That has a capacitive reactance of about 1500 ohms at 60Hz.  One might think that would consume 9.6 watts (watts = voltage squared / resistance.)  But the 80mA of current is out of phase with the applied voltage, and results in virtually no power consumption.  It does produce 80mA of heating in the wiring running to it, and any resulting dissipation is a loss of real watts.

Jeff

[dhouston]

It is also interesting to compare the VA and watts readings.  VA measures the heating stress to electrical conductors and inductors in X10 filters, and watts measures energy actually consumed.  For low power-factor devices, the VA reading can be several times higher than the actual watts consumed.  That can cause a lot more heating in an X10 filter than the power consumption would lead one to expect.

The Kill-A-Watt can measure everything of importance - not all at the same time, of course.

It measures Volts, Amps, Watts, VA, PF, Hz, kWHr & HH:MM (Elapsed Time).

[dhouston]

Not having much of an electrical background, that's interesting but meaningless to me.

Then you should spend $20 for a Kill-A-Watt meter in order to supply useful information to those here who do have an electrical background as it will help them to provide meaningful advice.
http://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=sr_1_1?ie=UTF8&qid=1462837196&sr=8-1&keywords=kill+watt

[bkenobi]

I've had one for a couple years and for the things it measures (that I understand) it's great!

[dhouston]

I've had one for a couple years and for the things it measures (that I understand) it's great!

I suspect that you and others have the most difficulty understanding PF, VA, W & kWh.
Here are concise explanations of PF & VA:
http://powerfactor.us/whatis.html
And here is a less than concise explanation of Watts & kWh:
https://en.wikipedia.org/wiki/Kilowatt_hour

[dhouston]

So while it causes heating in the wires (and X10 filters), it does not result in any additional power consumption.

That heating in the wires does, as you note, affect the wire size needed and is the reason why most commercial users have a demand meter which measures peak current, allowing the utility to apply a surcharge to compensate for the heavier infrastructure needed to supply that peak. Most industrial sites will employ power factor correction in order to reduce that surcharge.
https://en.wikipedia.org/wiki/Power_factor

[bkenobi]

So if I have a 15A circuit with 14ga wiring in my home and install a <15A inductive load, I could smoke my wiring without popping the breaker?

[dhouston]

So if I have a 15A circuit with 14ga wiring in my home and install a <15A inductive load, I could smoke my wiring without popping the breaker?

Breakers and fuses are current based so they should prevent any smoked wiring in your scenario.

The current is real but because it is out of phase with the voltage, it's the V*A product that is only apparent. It's devices whose ratings are not purely based on current that are likely to be smoked. Breakers/fuses are rated for current (i.e. Amps) not power (i.e. Watts) nor apparent power (i.e. Volts * Amps).

[JeffVolp]

So if I have a 15A circuit with 14ga wiring in my home and install a <15A inductive load, I could smoke my wiring without popping the breaker?

As Dave said, you would be fine using the current rating.  But that inductive load might have a 500W power consumption number.  One might think that only pulls 4 amps, and that is what causes us to overload circuits (and X10 filters).

Out of curiosity I just measured one of the old-style twin-bulb fluorescent lights in my workshop.  It uses two "energy efficient" 34-watt bulbs and a magnetic ballast.  The Kill-A-Watt measured 57W consumption, and 101VA.  One would expect the two bulbs to consume 68W, or .54A.  It is actually pulling .81A, but some of that is inductive (out of phase).  Using that .54A number, one might think it is safe to feed 8 of them through a 5-amp XPPF filter (4.32A), but the set would actually be pulling 6.46A, clearly overloading the filter.  Since many of the loads we place on X10 filters have a relatively low power factor, that is why we should stay well under the 5-amp rating.

Jeff

[bkenobi]

Ok, so it comes down to calculating the current from the other available information and making incorrect assumptions.  If the device lists current, then that will be an acceptable peak value to use when sizing things.

So since incandescent bulbs are basically small heating elements which should be 100% resistive and 0% inductive, it should be safe to add up old school bulbs to determine how many can be on an X10 (or any other) switch.  If the maximum number of incandescent bulbs are installed on a switch with no margin and then later changed to CFL or some other type of bulb, does that mean you need to check to make sure it won't overload the circuit?  I've never thought about it, but then I've never had that many bulbs on a single switch to my knowledge.  If it were possible to overload by updating, that seems like a safety concern that should be on the box of bulbs, right?