Static discharge on grounded circuits?

[sjp42051]

I was called to a residence with complaints of light switches shocking the home owners. (From touching the metal cover plate screws) I experienced the shock when I was there. It seems to be static from rubbing feet on the floor. The strange thing is when the circuit is off, there is no static shock. This occurs over multiple branch circuits throughout the house. The house was built in 2014 and is grounded, although I did not take an official resistance test. I'm wondering if the circuit conductors are inducing a charge on the ground wire and causing the static shock on the metal parts of the switch. Would the ground having a parallel path on the neutral cause this? I have not come across this before and am unsure of the solution. Thanks for any input!

 

[letgomywago]

What's the floor material? Stained concrete or some insulating material? Could be that the switch wasn't ever bonded to the screw and the wire is over stripped and touching the yoke.

 

[infinity]

Is it a static shock that only happens once when you touch the screws or is it a continuous shock like something is energized? When you say that the system is grounded how did you confirm that?

 

[Speedskater]

Is it a instantaneous zap? or a faint continuous buzz?

 

[Sea Nile]

This is odd, are you sure it's static?
What's odd is that you don't get zapped with the power off.


Can the spark be seen if you can make the room dark enough? Can you hear the popping sound associated with a static spark?
Do you still get static spark when barefoot? And ditto what letgomywago said.

 

[sjp42051]

The floor material is a laminate with some sort of plastic or vinyl top coat which creates a lit of static. I have yo physically drag my feet on it to cause the shock and once I touch the switch there is an audible "pop" just like a static discharge would cause. I then have to drag my feet on the floor again to cause another shock. And only when the circuit is on.
Breaker trips when hot touches ground. Doesn't mean that the ground isn't tied to neutral somewhere upstream. So I assume it's grounded. I would have to investigate more. My meter did read continuity between ground and neutral though, however I thought maybe because it was close enough to the main panel, it was picking up that main bond.
Also, this is occurring on more than one circuit. It seems everywhere that the flooring is, the shocks occur. I have never heard of this happening on carpet, so I'm inclined to believe that it's an electrical issue.
Thanks for all the replies

 

[winnie]

Ok, so the light switch _when on_ shocks people, but not when off?

Are these by chance dimmer or smart or illuminated or otherwise powered switches, or just plain mechanical on/off switches?

Does the customer get a sustained shock or a single zap and then nothing?

One possibility: the switch is not properly bonded to the EGC. The switch is the sort which tries to use the EGC as a current path for the control logic. (Switches have (had???) an allowable leakage threshold, and some 'clever' designers intentionally use power supplies which require less current then this allowed leakage, intentionally using the EGC to carry current.)

-Jon

 

[ptonsparky]

Shut the switch off. Walk around the house with the intent of building static. Go back to the switch and let us know what happens.

Whip out your Fluke 87 with Min/Max record selected. Make sure your range is high, DC. Walk around, building static. Hold one probe in your hand move the other to the plate screw.

You have static. Nothing more.

 

[ptonsparky]

What is the humidity level in the home?

 

[sjp42051]

No smart switches or dimmers that I saw. Whether the switch is on or off the shock happens. When the circuit is deenergized, there is no shock which is why I was thinking there was some sort of induction happening somewhere. I'm not sure of the humidity level in the house but it seemed dry I guess

 

[synchro]

I have yo physically drag my feet on it to cause the shock and once I touch the switch there is an audible "pop" just like a static discharge would cause. I then have to drag my feet on the floor again to cause another shock. And only when the circuit is on.

When the circuit is turned off, are you sure that there isn't any static discharge with a "pop"that still occurs, even though there's not a significant shock that's accompanying it. The reason I mention this is that maybe a static discharge could be enough to initiate a current path through ionization of the air, and then poor bonding allows some 60 Hz current to temporarily flow through this ionization path as long as it is present. If this is happening, the transient of 60Hz AC current could be more perceptible as a shock than just the static discharge itself.

 

[sjp42051]

Yes I'm sure. That's what's so baffling to me. Although it sounds like you're saying the 120V circuit could be exacerbating the static discharge?

 

[LarryFine]

I would start by checking the integrity of the grounding with a solenoid tester and an extension cord.

 

[letgomywago]

I would start by checking the integrity of the grounding with a solenoid tester and an extension cord.

Didn't think about that just because there's continuity doesn't mean it's not high resistance. I still think it's 100% static though and unless they want a metal floor or to change the humidity it's kind of a mute point for the electrical system. Canada does make and use nonmetalic plate screws maybe that could be used here to solve the issue.

 

[sjp42051]

I did order some plastic screws but am curious to look further into the electrical. Thanks for all the good input and discussion everyone

 

[suemarkp]

Maybe run an insulated ground wire from the panel into that room. Touch that wire (bare end stripped) instead of the switch plate and see if you get a shock. Try again with the lighting circuit off. That should at least isolate the ground problem from something in that box or circuit to just touching any ground.

 

[sjp42051]

I will look into it further when I go back and let everyone know what I find. Thanks for all the feedback

 

[Sea Nile]

unless they want a metal floor or to change the humidity it's kind of a mute point

Thinking outside the box want to try an experiment? Try spraying this on the floor and see if it helps.