Measuring impedance of wall socket

Hi, I'm not sure this is the best forum to post this question in but I was wondering how one would go about measuring the impedance of a wall socket? (Strange question, I know) I have some general ideas but would like to confirm my thinking. Any websites or other resources explaining the general concept would be greatly appreciated. Much thanks in advance.

Poke your dvm probes into one side of an outlet, and plug a toaster or similar big resistive load into the other. Measure how much the voltage droops when you fire up the toaster.

Impedance is pretty much droop_volts/load_amps.

John

The impedance means the ratio between voltage and current plus the phase between them. So first you have to get rid of the DC stuff, also the 50/60Hz with a set of capacitors. Then take a sweepable or fixed frequency source and measure the voltage, the current, calculate the ratio and the phase.

Rene

My oldest son, when he was like 3 years old, did the impedance test using a bobby pin ;-)

...Jim Thompson

Hey, everybody do this measurement and report what you get. The toaster thing, not the bobby pin.

John

Not a strange question at all, the only thing I find strange about line impedance testing is how few testers are on the market and how few electrical inspectors use them, considering how well they uncover the most common and dangerous wiring faults (high impedance connections, a common cause of fires) which are not otherwise easy to detect. A google search on line impedance tester will however turn up a few commercial testers.

If I were to build one I would use a bank of motor run capacitors for a load, sized for about 10 A at 120 V for measuring typical US 15 Amp wall socket impedance. By applying the load to Line-Neutral and then Line-Ground voltage drop can be measured separately for all 3 conductors. Since the change in neutral to ground voltage provides the voltage drop on the neutral or ground (whichever is carrying current), the rest of the total voltage drop is due to the Line (Hot) conductor impedance. Any other means of applying a load and measuring voltage drop at a known current can acomplish the same thing.

He's a coward! I did it with my thumb! ;-P

Gum wrappers, however, do make a cool spark. ;-P

Cheers! Rich

I've done this at my last two jobs, but the measurement was made at the service entrance, and not at some wall socket. Both times, the result was about 1/10 ohm (in the US, at 120 volts). This is at 60 Hz. Rene suggests that by asking for "impedance", the OP wanted to know the result over a band of frequencies. I didn't have the equipment for such a measurement, but I did find a paper where someone had done it. The result was a wildly varying impedance vs frequency.

was

socket?

My son tested the outdoor socket on the back of the house with a weedpuller, and found it full of sparks, until the GFI breaker popped . Since I was not using any electric devices in the backyard, I didn't know about it for several days. Then the backup refrigerator in the garage, which is on the same circuit, started to smell funny.

The booby pin went off like a flashbulb. Fortunately just a mild burn to his palm. But lesson learned in true Thompson tradition... the hard way ;-)

Don't you just love those occasions? I had a freezer in my carport storage room... no cooling... exposure to 120°F+.

So the connector failed where the compressor plugged into the thermostat assembly.

I don't know how many weeks later the wife comes screaming into the house... "You have to clean it up." Gag.

So I replaced the connector and moved the freezer inside to a hallway adjacent to my office.

...Jim Thompson

Do you happen to know why not?

Most modern UK installations have an RCD on the socket rings, and this test would send it flying.

Paul Burke

The impedance always belongs to a frequency. You're measuring at line frequency here.

Rene

I performed "Tickling the dragon" by dropping a K2 neon bulb with the conductors slightly spread apart through the blades of a plug.

Refrigerators are not supposed to be on GFCIs (there is an exemption for them).

I did it with a butter knife across the blades of a plug. My son found a brass ball at the end of a pull chain fit nicely into an empty light socket (and made a nice sizzling and sparking, which left some welts on his leg). Do girls do stuff like that?

Best regards, Spehro Pefhany

entrance,

US, at 120

OP wanted to

such a

a wildly

I worked with X-10-type controls a while back. and I recall hearing that "the" line impedance at 120kHz was 6 ohms. I never tested this myself, but in retrospect, I (actually the guy who was designing the hardware) should have. You may find more info on power line impedance by researching power line carrier (PLC).

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I'll bet you didn't have to tell him not to do that again! ;-)

For exactly the reasons above. False trips are more costly than any safety offered. AIUI, the outlet must be single-use and behind the unit (so it's not a tempting target for a weed-whacker).