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View Full Version : Why a small shock through a switch that was off?



leejosepho
12-21-2008, 05:37 PM
I just added a new circuit in my basement, and I am sure I did everything correctly. I ran Romex to a junction box, then wired down to a switchbox box with two switches. One of the switches is lighted when off, and I had the power on while attaching its single light a few feet away ... and I got a very slight shock between the bare ground wire and the black while stripping the end of the black wire. With the box grounded, the switch was lit up while the run to the bathroom light was still completely open, and I had assumed no power would be coming through the switch while it was off. So, what caused that bit of current that gave me a slight tingle? What I felt was so light that I first thought it was just from my arthritis or whatever while squeezing the wire strippers.

jar546
12-21-2008, 07:24 PM
Unless the circuit is shut off, all switches have power to them whether they are on or off. The power is always there waiting to be sent to the fixture.

jwelectric
12-21-2008, 07:31 PM
I just added a new circuit in my basement, and I am sure I did everything correctly. I ran Romex to a junction box, then wired down to a switchbox box with two switches. One of the switches is lighted when off, and I had the power on while attaching its single light a few feet away ... and I got a very slight shock between the bare ground wire and the black while stripping the end of the black wire. With the box grounded, the switch was lit up while the run to the bathroom light was still completely open, and I had assumed no power would be coming through the switch while it was off. So, what caused that bit of current that gave me a slight tingle? What I felt was so light that I first thought it was just from my arthritis or whatever while squeezing the wire strippers.

Current flowing through the pilot light on the switch

leejosepho
12-21-2008, 07:44 PM
Current flowing through the pilot light on the switch

I suspected that, but I would think "off" would actually mean "off"!

So then, there is always some current flowing through the light bulb on down the line even when the switch is off and even though the pilot circuit is already complete through the grounded switchbox?

Cookie
12-21-2008, 07:57 PM
Never assume my friend.

Cass
12-22-2008, 03:41 AM
Were you using uninsulated wire strippers?

jimbo
12-22-2008, 03:56 AM
I suspected that, but I would think "off" would actually mean "off"!

So then, there is always some current flowing through the light bulb on down the line even when the switch is off and even though the pilot circuit is already complete through the grounded switchbox?


The pilot circuit is NOT completed through the ground connection. It is never allowed to run any current to ground. The small current used for the pilot flows through the circuit load (light bulb, or your body!).

This is why switched like that will often cause flakey operation of fluorescent bulbs ( flicker, etc).

Thatguy
12-22-2008, 06:59 AM
Current flowing through the pilot light on the switch

Yes. The 1 mA that passes through a neon lamp is just perceptible.
I don't think most phantom voltages can deliver enough current to be sensed, unless you got the shock at the end of at least 200' of Romex.

leejosepho
12-22-2008, 03:59 PM
Were you using uninsulated wire strippers?

No, but I was touching some of their exposed area.


The pilot circuit is NOT completed through the ground connection. It is never allowed to run any current to ground.

I understand, but it did first light up even before the fixture and bulb had been attached ... yet now the pilot goes out when the bulb is removed from the fixture at the end of the line. Go figure, eh?! Overall, it just surprises me that "off" does not always really mean "off"!


I don't think most phantom voltages can deliver enough current to be sensed, unless you got the shock at the end of at least 200' of Romex.

The shock (barely a tickle) was at the end of a 35' piece, and now that I see the switch's pilot goes out when there is no bulb at the end of the circuit, everything seems fine.

jimbo
12-22-2008, 07:14 PM
I disagree that this would be referred to as phantom voltage. It is real voltage. There happens to be a high resistance in series, which limits the current which can flow through your body.

This probably also reinforces the idea that a switch should not be relied on as the means to remove power from a circuit prior to work.