Measuring impedance of wall socket

and

Both good points. If you build a uP controlled tester with a couple of fast simultaneous sampling A/D converters for voltage and current, and apply the load close to midpoint between voltage zero crossings (at a voltage peak) with a fast solid state switch, you could probably get enough samples to estimate impedance vs freq over a reasonable range before the RCD (GFI in the US) trips. But the short sample period would defeat part of the purpose of the high current test load, which is to heat up any high resistance connections which will often change resistance noticably in under a minute of high current testing, at least from what I remember of an article on line impedance testing I read in EC&M a decade or two ago, probably written by an impedance tester salesman of course. You could still do the sustained high load test on Line-Neutral of course. And while you were at it you could put a separately switched low current load to ground in to test the RCD.

This may be more than the OP wanted to know; the toaster with multimeter approach should work fine unless you want to do a lot of testing or investigate power line comms or lightning surge control.

On Fri, 29 Jul 2005 16:30:45 -0400, Spehro Pefhany wroth:

I knew a girl once who sizzled when she sparked. She never left welts on my leg but I did get some scratches on my back.

Jim

This reminded me of something. I didn't witness it, but my aunt once told a story about when her son, at maybe the age of three, managed to unplug the phone cord from the phone, and stuck the end in his mouth. She noticed this about a millisecond before the phone rang, at which point she said he "went ballistic."

Another thought...

Is he an engineer now? :-)

I often wonder which is the cause and which is the effect. When electrical engineers tell stories of doing things like this when they were a kid, I wonder if they did it because they already had some engineer in them, or if that was the event that turned them into an engineer...

Big software guru in networks.

Good question. I was always taking things apart when I was a kid, got in a lot of trouble over that ;-)

...Jim Thompson

Some serious fraction of the gadgets I buy have to be re-engineered some before they work at all!

John

I was always taking things apart when I was a kid, still do sometimes just to take a peak...

That's where I got myself into trouble, taking apart spinning wheels, pedal-type sewing machines, and wind-up clocks ;-)

...Jim Thompson

It's the putting it back together that's tricky isn't it ?

Graham

That was why I took apart dead radios and TV sets, then sold the ones I fixed. After that, I was working in a TV shop at 13 after school and Saturdays.

As did I. My father (an EE Prof) didn't take too kindly to me not being able to put back together his typewriter, when I was six. His cow-orkers told him that he should treat me as a son, not a grandson. I tagged along with him whenever possible (until he died, forty years ago).

I'm told that at the age of 3 ( too young for me to remember this one ) I managed to dismantle a railway carriage lock on the return jouney from London. My parents found themselves trapped and had to call for assistance !

Graham

One method, pertinent at 500KHz and up;

"Technique for Measurement of Powerline Impedances in the Frequency Range from 500 kHz to 500 MHz" Kwasniok, Bui, Koslowski, Stuchly. IEEE trans Electromagnetic Compatibility V35 #1 p87-89 Feb'93

Their rough results show peaks and dips between 10 and 1000 ohms over the band - Peaks at 2 and 20 MHz, dips at 4MHz.

You could use a safely-coupled/limited/filtered spectrum analyser to generate this data, outside of the powerline frequency, as with any two-wire network. An HP 3577 used for this shows a range of impedances between 10 and 500 ohms.

At the line frequency, a rough idea can be obtained by monitoring voltage distortion (as delta V) vs current drawn (delta I) for any power component with a capacitive input rectifier.

RL

service entrance,

the US, at 120

OP wanted to

such a

a wildly

Time out, to think about this. How could there be a single value? Different sizes and lengths of conductors can exist from circuit to circuit, and different loads could be connected on any given circuit or from circuit to circuit. The circuits can be wired with NM, or AC or in conduit, etc. Each junction causes an impedance bump, and the number of junctions as well as their physical layout varies. Attached equipment could have LC line filters or be purely resistive.

I think the question has to be crisply defined to get a definitive answer.

Ed

I agree, which is why I put the word "the" in quotes. The 6 ohms is a very rough, average, ballpark number, I have no doubt it can and does vary a lot.

-----

I have this problem you see. My wife kicked me out of the garage, and now i have to work in the garden shed. The only problem is that I dont have a rubbish bin, so my shed is slowly being impeded by beer bottles. So therefore the impedance of your wall socket is determined by how mauch beer you drink and how often you clean out the shed. What the f*ck is a wall socket? Is that one of them things you plug the vacuum cleaner in, or is the tv antenna socket thing. I even have a wall socket in my joint that you canplug a gas heater in....BURP...

The impedance depends on the frequency, and I don't know your application.

Back in college I designed a number of carrier current transmitters that put the local college AM station directly into the power line. That was a bitch. At 500 khz there are a LOT of random variables....

Lots of wireless intercoms use the power lines inside a house for coupling, and the line impedance is important at the frequency of interest, which is high enough to be considered RF ........

If you are only worrying about the 60 hz line impedance, you will have less of a problem (grin).

So you see, the application dictates what the answer will be.

You will get plenty of answers here for the 60 hz measurement.

Andy

That would depend entirely on what equipment was plugged in nearby.

Older daisywheel printers could take out X-10 systems for hundreds of feet.

Line impedance also, of course, is highly frequency dependent.

The neighborhood transformer arrangement would also be a factor.

service entrance,

the US, at 120

OP wanted to

such a

a wildly

Any decent line filter on any old printer or whatever will totally trash the line impedance at 120 kHz.

Assume it is zero.