Why Did This Outlet Still Have Power?

You ruled out a capacitor, but did you rule out a transformer?

I have no idea where to even look for a transformer. The power comes into her ulitilty room from the attic. There is a Blk. Wht. and ground on one sideof the switch and single black on the opposite side.

? ? ? ? Transformer ? ? ? ? ?. . . . on the light fixture outside ? ? ? the Light sensor ? ? ? ?

A transformer can only return stored energy for a very short time, unless there is something I don't understand...

The time required to take the cover off the switch is far more than the time a transformer could store energy.

It sounds like there is a photo sensor, or possibly a motion sensor. The photo/motion sensor will require a low voltage power supply of some kind, which is almost certain to contain a capacitor...

Always wear gloves when handling any electrical wiring.

Did you hook everything back up and did you turn the power back on and try to duplicate the arc under more stable conditions?

Is there any other power source that could "back-feed" into the system?

The, "would NOT fully switch OFF" statement indicates a big problem. It should be on, or off. if wired properly.

What did you mean?

The swithc was probably 20 years old or older. It simply would NOT go all the way into the OFF position.

You mean the light fixture may have a small capacitor inside the fixture?

That's it. GA.

It looks just like this.

One single No. 14 x 3 wire coming out of the attic into the wall.

A Blk. a Ground and A Neutral on one side, a single Blk. on the other side.

Wiring goes out to the fixture....just like the one shown here.

That looks like an older fixture with a CdS (cadmium sulphide) photodetector. Usually the circuitry in those included a capacitor to provide a time lag so that the light didn't trigger from a passing car's headlights.

Nothing is ever dead until the leads are shorted together and a voltmeter verifies it.

Lesson learned! I would have never guessed something like that.

The wholelight fixture is dead tonight.

Switch is rewired and OK, but the spot lights are not operating. The fixture is old. Probably shorted something inside.

I can only guess. This house was built in the 1940's and has been rewired by who knows how many people.All is well.As for now the outlet with switch is OK. Light outside is not. I will take off the old fixture and get back to the single romex x 3 strand that i see coming out from the attic. I should have power there. ...I know I have Yellow Jackets!

Personal Safety First!

Now that you are not sure where the original power came from, and rather chase your tails trying to find out where that power that initially shocked you also came from, it would be a lot easier /simpler for you to run a new set of 3 wires (BX /Romex) type. Connect the new wires back to the main breaker box that you know where power should be coming from... But be sure that the mains is really OFF before touching anything!

Since there is no longer power coming from the unknown old wires, (since lamp still didn't work after switch replacement), the old wires can either be pulled out completely, capped or shorted together for safety...

All circuits need a return, but you describe a single black coming out of the switch. My guess is therefore that the return circuit comes out of the back of the fitting and finds a different way back to the distribution board (against the UK wiring code for this very reason). Somewhere along that way it has been commoned with the return from another fitment which was live at the time. The fuse protecting that second fitment has now blown.
As for capacitors in power supplies, these are not present in the input of either transformer or switched mode power supplies. The capacitors used to stabilise the DC output cannot drain back to the input.

I am not fully understanding your description of what happened. However, this house has circuit breakers, no old type fuses.

After I reinstalled a brand new switch, the swithc has power but the light does not work. I HAVE NOT un-done the circuit box and removed the old light fixture as yet.

I will test the wires when i do ( after i kill them dang yellow jacekts!).

If something is still amiss, I'll call in someone qualified.

Thank you for the comment.

There are a lot of low power devices that do not use SMPS or transformers when line power isolation is not necessary.

Here is a basic schematic of a capacitive coupled power supply which is very common on things like outdoor lighting control circuits and other line powered devices that have very low power requirements.

If the manufacture went with a high value resistor across C1 the self discharge time could be on the order of 10+ minutes or if they were really cheap, which I have seen many times, they may have went with a design similar to what this schematic shows and had no self discharge resistors at all.

So yes the dusk to dawn circuit in the OP's outdoor light could very well have had a small capacitor in it that could have stored enough charge to produce one good POP when shorted out! A .5 uF or more low ESR capacitor charged to 160+ peak volts, like any common 120 VAC power line carries, can easily make one good and surprising spark!

If the OP's in part of the world that uses a nominal 220 - 240 VAC the peak voltage could be up around 300 - 350+ volts allowing for an even smaller capacitance to still give a good hot and surprising spark.

High pressure sodium outdoor lights have capacitors....

Metal halide lights have capacitors....

Mercury vapor and low pressure sodium lights can have capacitors.....

Nothing that big.

Have you replaced the switch, and is everything OK?

I'd not worry is this is the case.

Nope, not at night I'll do it tomorrow while she is at church and I can kill everything again.

Replaced the switch today.Power to the Switch, nothing at the light fixture. I taped the photo cell black and no light.. . . as of tonight, still no light.

I'll pull of the fixture next week end and replace all. I hope I have power inside the junction box . I really do not want to start pulling wire inside that low little attic.

As a side note;

* broke a shock on my truck going into town for parts......hit a leaf covered pot hole you could have hidden an Abrams in.

** Got the $h!t stung out of me by a nest of yellow jackets hidden just under the eave by the light fixture

I can't wait for Monday to start! Its got ot be better then thuis week end!

In such cases, where we are unsure whether there is a capacitor in the system or so, how do we "kill the power" completely or be sure there is no stored charge in transformers or capacitors waiting to hit you?

I understand the precaution of working with gloves and everything, but apart that?

The light he has looks like a standard incadescent type. The photocells on my lights have no capacitor, they are thermal bymetalic strips and the thermal time causes a delay. Transformers discharge their energy in milliseconds. By the time he has killed the main power any capacitor should be discharged within about 5 seconds (code requirements).

I still think the power is coming from somewhere else that we don't know about-

(Power saver - it is on the line side of the meter?)

Is there a capacitor on the HVAC fan?

do not know.

Yes, there is an AC, a refrigerator and a well pump on this property.

So are you saying that before touching the hot wires in such a case, we should short the neutral and hot for a few seconds or so before proceeding to work on them?

When not having a measurement device, these are handy, but must be used correctly.

Yes, but verify that there is no power via a multimeter first. This is because most modern meters are very high impedance and would not necessarily discharge an upstream capacitor. Touching the wires together will discharge any capacitors waiting on line to bite you.

Note that I am making a distinction between power as one would see on a live line as supplied by the electricity utility and the presence of a charged capacitor on the line. There is really no difference but the operation of a meter when checking for charge from a capacitor may not be reliable, as I pointed out in my first post. However, you can place high reliance in a meter to detect the presence of utility power.

If you have a high quality meter that you know responds reliably and detectably to capacitor charge then these comments can be pretty much ignored. You will know there is some voltage on line and can then take steps to deal with it.

But, without that expensive meter, momentarily touching wires proven to have no utility power to them will guarantee that any capacitors on the line are discharged.

Jon.

I would look for an inconsistant surge coming in on the neutral ground. This is especially true when you are located in a rural situation.

I know I will get Poo Pooed or laughed at, but I milked cows in a very rural area, in the Northeast US the neutral carried 45volts "inconsistantly" on the neutral off the public power supply.

The cows were/are extremely sensitive to low power surges of this sort because they are well grounded, especially on a wet concrete floor. This stray voltage cost me many thousands of dollars, due to cows reluctance to produce milk in a milking parlor under these conditions. Multiple grounding rods are required to circumvent this problem. A stray voltage monitor is required to detect this sort of power source.

Understood. There are a few items like the fridge, AC and well pump hooked into the house's utility box outside...... Any of them could be the culprit.

static electricity, you are wearing a nylon and cotton and touch the wires and gott sappet with a static current, and in the dark and working on the power outlet you thought in your mind that you did got it from the grid somehow. atliest my theory...

You could be right, but I've never seen a static discharge that blue, smell of ozone and burn like that did.

it could be that someone tied into the power Before the meter and hid the connection.Disconnect the light and check and see if you have power when you turn on the mains, Also should be FIRST check for power before you turn on the mains.Next if it is tied in before the mains someone could have put a fuse in between the light and the main connection.and it blew.and that could be why you dont have power if you turn on the mains. Go and buy yourself a Meter also.

Thank you for the heads up.

I will untie everything next week end when I return for the 'rest of the list' of to-do's at Mom -in-law's house.

I have two meters ( probe type) They did not register anything .

Is there something more accurate and reliable for house-hold current jobs like this?

If you don't already have one, get a Fluke VoltAlert or one of the several other brand similar devices. I never work on power circuits without first checking. These devices detect the presence of potential, whether there is any current or not. You simply hold the tip of the device near (does NOT need to touch) a wire, and if the wire carries a voltage, it will flash and/or beep. They are available for various voltage ranges. They are cheap ($15-25) and reliable, although you should always check on a known live wire every time you use it to indicate the absence of voltage. I have a Greenlee GT16 that is rated for 5-1000 VAC; one problem with it is that even though it has a sensitivity control, I can't get the sensitivity low enough to be sure which is the neutral or hot within a single cable unless the wires are separated. With the Fluke, I can. In fact if you run the Fluke along a standard twisted power cord, you can tell how tightly the wires are twisted, as the light will come on each time the hot wire is on the side of the cord nearest the sensor, and go out for the neutral and ground wires.

On the other hand, if your spark was caused by energy stored in a capacitor, that would be DC, and I'm not sure just how any of these devices respond to DC...

Shop secondhand/pawns for a 'wiggie'...i.e. a Wigginton volt tester...it's a solenoid type tester for ac/dc, the solenoid pulls against a spring and a scale pointer on the side indicates the voltage, a flip magnet on the top indicates polarity. Good to 600v ac or dc. Used to be in every electricians bag until modern 'digital' meters. Not much use under 80 volts.

Bees, wasps, and hornets won't fly after dark or when it gets cold.

It sounds like you may be dealing with a "hallway" circuit with that second black wire, and need to use a 3-way switch. Is there a second switch that operates that light?

The Romex 3 strand comes out of the attic into a switch circuit. It is connected with BLK. WHT and ground on one side and s single black on the other.

Until I take off the fixture outside, i will not know.

I am waiting for supply delivery so I have some slack time. I just might head over there in a little while and pull the thing off the eave and see what's what.

The flash came from your personal magnetism mate,not the electric.

It sounds like you are already in the habit of working one handed, but if that isn't the case, it is a good time to take up the habit.... Just put your other hand behind your back.

Getting shocked still won't be pleasant, but it is far less dangerous if it doesn't cross your heart.

.

Also, it is a good idea to 'tag out' any breakers your open, in case someone comes home or forgets and decides they should fix the power outage. Something as simple as masking tape over the opened breakers could work.

I realize that is probably not what happened in this case, just a friendly reminder.

Well, I just came back frmo Mother-in-law's house.

I traced all the wires and found no issues.

Straight forward , a light fixture feeding off of a light switch receptacle.

However, when I went to put the power back on, one room stayed dark. I went back over the breakers and turned each one off and on again.... it seems there was one breaker that is weak. . It did not spring back as hard as the other ones did. It is warm to the touch but not overly hot. I do not know if this contributed to the flash, but its good to know so i can change it out anyway.

You know what the absolute funniest thing about this situation is? Mother-in-law has 2 electrician grandkids (one certified to work off shore) , one certified for air conditioning and a third who is a Electrical Engineer. All 3 live within 5 miles of her house. Still she insisted on having me come look at it. Go figure.

Thank everyone for the input. As usual, I learned a lot . I always do on this forum. Its simply the best place to go any kind of advice. thank you all again.

*Saia freight is delivering supplies tomorrow... I am sooo glad to get back in that hot @$$ shop and sew some nets..... Thank Everyone again.

CR4 trained - beats even the best schools!

Since everything else has been covered. And it hasn't happened again.
Could it have been a static discharge?

Always a possibiliy I suppose. Hopefully I will not have to find out again and all is good for now.

It's not too unusual in older houses to find "undocumented" circuits. If there is one and the house still has switches on the return (white) rather than the power leg, it WILL give you leakage into the house wiring, leading to your situation. I had an early (1883) row house in NJ at one time and until I switched ALL of the switches to the power (black) wire, I had 60V AC in every metal switch plate. It was reverse feeding through the incandescent filaments. Prior to my rewiring, the house had a mix of switched legs and this caused the problem. I can only eonder just how much power was wasted (and billed) before that. What alerted me, was the 'tingle' I got every time I touched the switch on the bathroom lights. Since I found the same situation in other houses, I'm assuming that switches on the return were code acceptable at one time.

Thank you for the reply.

It is another lesson in my CR4 Training course.

you have more confidence that your Main was fully in the "off" position than I am, I'd be checking that long before searching for capacitors in lamps and transformers. just because you hear it click doesn't insure its been fully opened and no current path exists. something as small as a crushed bug in the contact area can provide an adequate path for enough current to floor you. It might not be enough for your lighting system but its enough to cause harm.

You are 110% correct. i was not being as cautious as i should have been.