Is my 220 volt outlet wrongly wired?

[radhak]

I have a new toy : the non-contact voltage tester from HF



First of all, I took some time accepting it's accuracy. At some outlets, it beeps and buzzes without even touching, while at others I need to sorta insert the nose in (like in the picture) to get the same reaction. When I tried some switches, I found the same level of distance-related variation.

Finally though, I have come to accept that it is more accurate that I had expected, almost to the level of calling it 'reliable'.

Now the problem : When I bring it near the power outlet for my lone 220v in the garage, it comes alive at both the left and the right sockets/slots (not at the 'earth' slot) ; this is not the case with any other outlet. I then tried it at the TS itself, where the power-cable reaches the box, same reaction. I touched the saw (foolish of course, with the doubt, but then...) and didn't get killed/electrocuted. The saw runs too.

So the question is - is this how the 220v should behave? or is there something to be investigated?

[billwmeyer]

If I understand your question correctly, It should show power on both the left and right socket, as these are both individual 110 lines thus making it 220. On you house outlets only the hot wire should show power. I am not familiar with that type of meter and my level of proficency in electricity is more shade tree type.

Bill

[Tom Slick]

220v in a 3 wire installation has two hots and a ground, no neutral. If it's a newer installation it will have a neutral that is straight across from the ground.

To think about it another way. If it's a 3 wire 30 amp circuit (like a dryer circuit) If the ground is at 12:00 the hots are at an angle at 4:00 and 7:00. If it's a 4 wire installation it'll have the ground at 12:00, hots at 3:00 and 9:00, and neutral at 6:00.

[LCHIEN]

yes, that's proper behavior.

[eezlock]

220 volt wrongly wired ?

No, it is wired correctly. Two hot wires and a ground.

[steve-norrell]

Correct and safe plug-in?

Is that the proper plug for a 220 volt outlet?

Steve

[mineengineer]

It wired right but........

those kind of voltage detectors woork pretty good but sometimes they will give you a false positive. On some wiring runs that parrallell each other (physically not electrically) a run that is de-energized will still give a positive signal for voltage if a live run is close to it and follows it for a few feet. I was wiring a two story shop once and was pulling new romex which was not connected to anything at either end and it showed a voltage because it was parrallelling a piece of romex that was live. You can also lay a piece of pipe a few feet away alongside a live wire and the pipe will test positive. I guess the detector is looking for 60hz ac signal and the emf field from another conductor can play games with the detector. For safetys sake check with a voltmeter to make sure there is voltage or not and always treat any unkown with respect like it was hot.

[radhak]

Thanks Link for the explanation - helps in understanding. Actually, it brings me to why I was doing this test : two days ago I replaced the stock power cable to my Unisaw with a longer yellow cable. This is slightly thicker, and has copper innards (the older black one had something silver - zinc, maybe?). I was very careful in replacing everything exactly as it was by color (took pictures first).

But with the recent thread about the women trying to 'shock' her husband, and Loring stating it would be easy to switch the wires to do so, I had visions of me touching the table top and ending up a black skeleton with spiky hair .

I ran the saw without touching any part of it and it ran fine. I waved/touched the voltage detector all around the saw and it stayed silent. So would you think it's safe for me to use the saw?

[Tom Slick]

with 220v you are fine; the saw won't run if you wired it wrong. If it were 110v and you connected hot to ground and didn't connect the neutral you could get a shock.

[Marv]

Back to what Steve asked. The outlet pictured does not look like a 220V. outlet. I presume that he was only showing the unit operating on a regular 120V. and not showing the actual 220V. outlet.

[radhak]

Oh yeah, that picture is not me - it's a stock pic from HF. My 240 volt outlet has the eery slitted-eyes .

[Jerry P.]

I use a tester similar to that every day at work.
It can test from 50V to 600V.
A good way to use it to test to see if power is off, is to test a known "live" outlet before testing to see if power is off, then again checking the "live" outlet. This checks tester operation!
You should also keep in mind that the tester uses batteries. If you don't use it for a good while,(months), remove the batteries to prevent corrosion.

Jerry

[eccentrictinkerer]

Thanks Link for the explanation - helps in understanding. Actually, it brings me to why I was doing this test : two days ago I replaced the stock power cable to my Unisaw with a longer yellow cable. This is slightly thicker, and has copper innards (the older black one had something silver - zinc, maybe?). I was very careful in replacing everything exactly as it was by color (took pictures first).

FWIW, the wire is copper, but is "tinned".

Also, the gadget you are using detects electrical "potential".

I recently checked a circuit that showed the hot wire was hot, but circuit was dead.

Turns out I had no neutral! Now I'm looking for a neutral detector.

[LCHIEN]

Radhak, if you wire a machine and are worrkied about being electrocuted, , its simple to check if its going to be OK.

The main thing that'll shock and/or kill you is touching an exposed hot contact point. Someplace that's wired to or connected by a short of some sort to one of the electrically hot wires.

In a 120V device this means that after you wire it together, you can use an ohm meter to check from the hot blade to any exposed metal points on the tool. Now, I can never remember offhand of the wide blade or the narrow blade is the hot one, but it doesn't really mater. Although only the hot is theoretically required to be checked, You should check both blades to any exposed metal points on the tool that you would be able to touch - Because sometimes the sockets are wired backwards - It would not surprise me to find that 1% of the sockets in the USA are wired backwards (that's another story). Any connection measuring under 100,000 ohms should be fixed. Actually it should be millions of ohms. But you have to be careful how you measure, megaohm measurements on a meter can be tricky-you have to avoid touching the metal part of the probes.

Now if its OK, check the ground if it has one. The ground pin on the plug is should be shorted (less than an ohm or so-many cheap meters have probes that are more than an ohm themselves) to the case and or any exposed metal parts. If it does not have a ground pin on the connector then the unit should be double insulated with a plastic case and basically constructed so its not easy to short any exposed metal to one of the hot wires with a single fault.

For a 220V device, its the same procedure, but now you really have to make sure both hot connections are not connected to the case.

For the record, the little wand device Radhak is describing is not a potential detector, but a potential Field detector. Potential is really the same term for voltage. A field is a property that an alternating voltage will have and is basically related to radio waves. There are also magnetic field detectors which detect alternating current in nearby wires and such - this is what makes motors go and clamp on current meters work.

Electric fields fall off very rapidly with distance and also can have dips and valleys caused by adjacent fields cancelling them out. So its hard to use the presence of a field as a indication of the strength or voltagin the wire but its useful for detecting its presence, espcially if yoiu move it around a bit to avoid thoses localized dips in strength.

[woodturner]

If it's a 3 wire 30 amp circuit (like a dryer circuit) If the ground is at 12:00 the hots are at an angle at 4:00 and 7:00. If it's a 4 wire installation it'll have the ground at 12:00, hots at 3:00 and 9:00, and neutral at 6:00.

Just a "heads up" that dryer circuits do vary in different areas, with different configurations of both 3 prong and 4 prong receptacles.