Gate keypad shocks people

[brweston]

There is a keypad on an automatic gate at a condo community on the coast. There is an ongoing problem with people driving up to it getting shocked. Before I was contacted they pulled the wiring totally out of the pedestal and it still happened. When they called me I immediately thought it was a static discharge from the automobile to the keypad via the driver. I suggested that they walk up to it and it does not shock a person on foot. I also asked them to discharge it and then back up to it from the other direction to see if it is environmental. It still shocked them. I am now pretty sure that my static evaluation is correct, but am not sure how to remedy the problem. I am sure other ECs have encountered this problem and I would appreciate any information on a remedy for this situation or let me know if you think it is not static from the car. Thank you.

 

[petersonra]

FL is pretty humid. hard to get much in the way of static in a humid environment.

Might be a nearby underground electric line that has failed insulation.

 

[growler]

One way that you will know if it's a static charge is the spark. If the spark jumps off the end of the fingers it's static because a static charge can be around 15K volts. 120V won't jump like that.

 

[don_resqcapt19]

FL is pretty humid. hard to get much in the way of static in a humid environment.

With my last pickup truck, I got static shocks getting out of the truck even on the most humid days we have here in Illinois in the summer.

Might be a nearby underground electric line that has failed insulation.

The fact that they don't get shocked when standing on the ground and touching the keypad seems to rule that out.

 

[GoldDigger]

...
The fact that they don't get shocked when standing on the ground and touching the keypad seems to rule that out.

Not necessarily. If there is an earth voltage gradient
1. A person in dry shoes might not have the same earth contact resistance as someone in the seat of a truck, and
2. The average distance of ground contact points from the pedestal will be greater for someone in a truck than someone standing next to the pedestal.

However, I think that theoretical exercise is going down the wrong road.

If the shock is repeatable on letting go of the keypad and then touching it again, then it is not static.
If you have a continuing sense of shock and not just an initial spark it is not static.
There may be something unusual about the pavement near the pedestal that makes a static buildup on the vehicle more likely.

 

[brweston]

Gate keypad

Gate keypad

A little more information. The shock only occurs on initial touch. It does not continue. I have requested pictures of the area, but I am told that the only power in the area is an overhead line about a hundred feet up the driveway. The company that owns the community has several other beachside communities with the same paving. Thanks for the input.

 

[gar]

150627-1451 EDT

Some experiments.

Use a high impedance meter.

1. Have someone drive car into position. Another person measures the instantaneous voltage from car body (a conductive location) to the keypad. Is there any instantaneous reading?

2. Same as (1) but short car body to keypad. Maintain the short. While shorted determine whether driver gets a shock by touching keypad.

3. If (2) and driver gets a shock, repeat (2), but have driver touching conductive part of car body, then while touching a conductive portion of the car does driver get a shock when touching the keypad?

.

 

[GoldDigger]

Good points. With some seat coverings the driver can build up a decent static charge relative to the car while staying seated.

 

[brweston]

Gate keypad

Gate keypad

Thanks for all of the input. I am aware of the (3) static situations rewiewed by Gar and have seen information that indicates that certain automobiles offer higher static than others. This is a community with high traffic and different people entering regularly. I was wondering if someone had an idea of how to stop it from happening. They have covered the keys with rubber cement, not pretty and tried several other measures. If defies some of the basic ideas about static and the situations that create it. There are some industrial products designed to prevent static in high speed machinery. Has anyone ever heard of an application like that that would work in this situation?

 

[ggunn]

I don't see how it could be anything other than static electricity. Someone in a car on rubber tires has no path to ground and could not be part of a circuit even if the pad were energized. Don't trucks often drag a piece of chain on the pavement so the drivers don't get shocked by static charge at toll booths?

 

[John120/240]

I don't see how it could be anything other than static electricity. Someone in a car on rubber tires has no path to ground and could not be part of a circuit even if the pad were energized. Don't trucks often drag a piece of chain on the pavement so the drivers don't get shocked by static charge at toll booths?

When I see chains hanging underneath a vehicle here is what you see 90% of the time. Often found on Fire Engines, Ambulances, snow plows. Do they as a secondary function reduce static shocks, I do not know.

 

[GrayHair]

I'm onboard with the static charge group. I saw power supplies go insane and crank out surprising voltages but don't remember anyone getting zapped. One system operated erraticly at nearly double the rated voltage, but usually the equipment got toasted. This is out of left field, but possibly something building/storing a charge as the gate operates? New rollers or guides if the gate slides?

It doesn't make sense. Which is why it will probably be a bear to find.

 

[Tony S]

Can the keypad be mounted so it is free of any ground connection, something like a wooden post?

The only sure way of detecting static is with a gold leaf electroscope, I haven’t seen one since I was at college 45+ years ago.

BTW
Tyres have had carbon in the composition for years.

 

[ritelec]

Free from any ground connection ???

Not always but often. If I drive the mrs santefe
When I get out of the car and close the door I get rapped. The car is on tires. I'm in rubber soled boots. ???

Was thinking like antennas coming out of the ground that you drive over and touches the car. Not sure if that would work as in my scenario I was in the car and the car gets me.

 

[ritelec]

A rubber pad over the keypad. Like the rubber pads they use to put on a cash register at a greasy dinner

 

[ritelec]

:- )

Has anyone tried using their tongue ?

 

[cadpoint]

It sounds like it's shorting on the extension arm or as said not isolated correctly
per design or a Gardner made a field splice for you to find.

Get the models numbers of everything involved!

Research the diagrams, research that everything is grounded on low voltage
side and not bundled with 120 V electrical. Make sure that the correct wire type
was used.

 

[don_resqcapt19]

...Don't trucks often drag a piece of chain on the pavement so the drivers don't get shocked by static charge at toll booths?

I haven't seen it in a long time, but 20 or 30 years ago, it was common to see the gasoline tank trucks dragging a piece of chain.

 

[Tony S]

A rubber pad over the keypad. Like the rubber pads they use to put on a cash register at a greasy dinner

That could well be the solution to the problem in hand. Inexpensive to add to the plus points

I haven't seen it in a long time, but 20 or 30 years ago, it was common to see the gasoline tank trucks dragging a piece of chain.

Not really necessary now as every country I can think of uses a resistance grounded hook up for the tanker before filling or discharge pipes are connected. The resistance preventing a sudden discharge of static from what is basically a big capacsitor.

All our discharge points had them. The drivers were a pain in the **** ****, driving off still hooked up.

 

[Fulthrotl]

I haven't seen it in a long time, but 20 or 30 years ago, it was common to see the gasoline tank trucks dragging a piece of chain.

farther back that that, but yeah, i believe it was for lightning protection.

the entire issue seems to be people in rubber tired vehicles
touching a grounded pedestal. all kinds of people, driving all
kinds of vehicles.

my thought is that vehicles are building up a static charge
approaching the gate, and discharging it on the pedestal,
and the pedestal is getting the blame.

if the pedestal had a charge on it, people in rubber tired vehicles
wouldn't notice any more than a pigeon on a 12kv line notices.

so, people are bringing the potential down the road, and dissapating
it on the pedestal. the question is, where are they getting it at?

we need more pictures and a full CSI forensics team on site, mister OP.