Still Having Problems with Static build up on Street Signs and Stop Lights.

[muskiedog]

I have been trying to get information on static build up on structures located under power lines. My highway works are receiving staic type shocks when touching the signs that are located next to a power distrabution hub.

Is there any PPE or some way to disapte the build up on these items? Anyone else experiencing this.

Power company won't give me much help. Very vague. I think they are worried about opening this can of worms.

 

[ramsy]

My Redwing safety boots are ASTM F 2413-05 STD "Electrical Hazard" rated (I think to 600vac), also helpful for positively energized grounding sytems that periodically hurt people. But, insulated boots won't stop positive-static discharge going from workers bodies into a neutrally grounded object.

A boot with the ASTM F 2413-05 STD "Static-Dissipative" feature is designed for working with sensitive circuit boards, and fab. plants, because these conductive materials disipate static charges. "Static-Dissipative" is not something we need with energized grounding sytems, since high conductivity invites electrocution.

Confusion aside, if expensive work boots aren't required for a project, nothing is most likely to be issued.

Most gloves don't satisfy any STD's, but if your shure its only static charge, to be better than nothing all a comfortable-leather glove needs is contact resistence to slow the rate of discharge.

Before experimenting with full OSHA fines and liabilities by issuing non-dielectric gloves, you must be sure its static, because an energized grounding circuit is not slowed by resistance, it just fry's the resistor.

 

[peteo]

From what I've seen you're in the right place. Try the mikeholt web site for 'stray voltage,' meaning induced from another source (buried power lines) rather than static buildup. It sounds from what you've written, directly related to the local power lines. There have been threads on this forum many pages long which can be searched for thoughts, guidance, and experiences.

 

[don_resqcapt19]

How are the signs installed? What are they made out of? How big are they? Have you ever tested for voltage with any type of meter?
Don

 

[muskiedog]

Yes we have tested the equipment.

Yes we have tested the equipment.

We have had them tested for stray voltage, etc.. Had a power company rep out but he wouldn't give any direct instructions on how to deal with this. These are your road signs metal post and aluminum blank and your metal stoplight posts over the street. It is worst on a rainy or high humidity days. Workers get a slight tingling and when in a bucket truck get static type shocks. WE did look at underground locations but all of this is coming from the transmission lines on the towers above. Electromagnetic induction I believe. The signs and posts are storing energy like a capacitor.

I guess I will provide linesmens PPE gloves and boots until we find a way to eliminate the problem.

 

[RayS]

very strange that it is worse with rain/humidity increase (if it is really static)

I'd wonder also about stray currents from the ground causing "touch potential". This is sometimes a problem with livestock under transmission lines (due to inadequate grounding?)

If it truly is static, bonding the structure temporarily to ground should help. I have had to do this in the past when mutual inductance in cable tray wiring induced an aggravating level of stray voltage in the adjacent, locked out cables I was working on.

 

[winnie]

IMHO this is a job for _bonding_ rather than a job for _insulating_. You can only get an electrical shock when you are touching items that are at _different_ voltages. Bonding is the process of electrically connecting all of the various bits of metal together, so that there isn't a chance of shock. An extreme example of this sort of use of bonding is used on high voltage transmission lines, where the line workers wear _conductive_ metal mesh suits which they attach to the high voltage line. (This is specialized, highly trained work, and not what I am advocating here; just an extreme example of the process.)

The problem that I see is developing proper procedures and safety tools to correctly deal with what are probably 'nusiance shocks' (shocks that are easily noticed, but which are not supported by the energizing circuit in such a way as to present a real risk of electrical injury), while at the same time not introducing real danger. You need tools and procedures that allow you to ground/bond these signs from induction or stray voltage, but which won't cause injury in the event of a real electrical fault. I presume that these sign workers are _not_ electricians.

Basically you need something that is as safe as the instruction given at gas stations: prior to putting the fueling nozzle into the car, you are supposed to touch bare metal of the car with your other hand to discharge any static electricity, getting the spark through your hand rather than the fuel vapor. You need a procedure that an essentially untrained sign worker can be told: use this tool, do this to the sign, and then you will be safe.

Question for the rest of the forum: do there exist tools for temporarily bonding metal objects which include the necessary protection from high voltage shock and arc flash? Do there exist tools to permit a sign worker to safely bond a sign without requiring electrical training?

-Jon

 

[kingpb]

This is a common problem resolved simply by grounding. Make sure the resistance to ground is 25ohm or less. One ground rod per sign should be sufficient.

Steel transmission line towers and poles are grounded for this exact reason.

 

[winnie]

I respectfully disagree, but must admit that this is a hunch on my part.

The impedance of the energizing circuit (induction, leakage through the air, etc. between electrical wires and the signs) is _very_ high; the sign support post is probably buried in concrete for a couple of feet, and even if this ersatz 'grounding electrode' has thousands of ohms to ground, the potential of the signs should be that of ground. My gut is that improving the 'grounding' of the signpost won't change the shocks in the slightest, or will perhaps make these shocks worse.

I would expect that the bucket truck (sitting on rubber wheels) or the worker (standing on what is perhaps a fiberglass ladder or in poorly insulating shoes) is being energized relative to the _grounded_ signs. In other words, voltage is being induced on the worker, who is then touching a grounded sign and getting shocked. In this case the solution is not grounding the sign further, but somehow grounding the truck or the worker before they touch the sign.

Perhaps something as simple as a ground wire reel used in aircraft fueling, run from the truck to the signpost.

The risk that I see is in attaching this grounding clamp, because if the sign really is energized and not well grounded (say a street light with an insulation fault), then attaching the grounding clamp could make for a very messy situation.

-Jon

 

[kingpb]

Winnie, your incorrect, sorry. I got the info about needing to ground them from our T&D group lead engineer here in our office.

 

[muskiedog]

Wouldn't the sign already be grounded? I think I agree with Winne! It could very well be that everything under these transmission lines is become charged. What is T&D?

 

[winnie]

With no further information I would personally _bet_ on kingpb being correct; he apparently works with others in this field, I am an electric motor researching making a guess. At the same time I would hold my own less experienced guess as an idea if grounding doesn't in fact provide the solution. My idea still feels right to me, but you have to weight that against the fact that I don't have much experience in this field.

A sign is not intentionally grounded with a proper made electrode, but is probably inadvertently grounded by the fact that it has a metal post sitting in concrete in the earth. The resistance between the sign and the earth may be hundreds or thousands of ohms. A properly made electrode system will have much lower resistance to earth. It may simply be that the signs are not grounded 'well enough'.

You will need to experiment to determine a solution, and there will be safety issues involved with any such experimentation. I strongly urge you to have a suitably experienced engineer working the problem, and not depend upon an open internet discussion forum for more than brainstorming ideas.

-Jon

 

[muskiedog]

Already have an engineer working on it. Just see what the forum had to say or experience. I was out yesterday looking at the signs and lights. We are going to place grounding rods on each corner of the equipment. What really amazed myself was that my AC power sensor stick 110-600v lights up whe you are underneath the transmission lines. Never realized how much juice is in the air.

Thanks for the help everyone.

 

[kingpb]

What is T&D?

Sorry, T&D stands for Transmission and Distribution, all high voltage stuff.

 

[winnie]

Muskidog,

Any updates on the 'shocking signs'?

-Jon

 

[robbietan]

the best advice I can give you is that let your people ground 'themselves' before touching anything static.
BTW - static has nothing to do with the power lines. power lines can 'induce' voltage but not static.

 

[muskiedog]

Update

Update

We are in the trial peroid of installing additional grounding rods for these structures. But I have recieved additional complaints from contractors that are re-painting the sign posts and stop lights.

No one wants to work on these.

Our employees are wearing PPE gloves to protect them selves until we verify that the grounding is going to work.

 

[cowboyjwc]

I have fixed problems such as this with a simple ground rod also, but and this is a big but, I did watch a show where the linemen ground their buckets right to the lines they are working on. Maybe if they just attached a jumper from the sign to the bucket that might disipate the charge. We used to do this in our plant where we would put a jumper from the building to the barrel and the barrel to the pump when transfering chemicals so that there would be no static discharge.

Just a WAG.

 

[RayS]

IMHO this is a job for _bonding_ rather than a job for _insulating_.
Question for the rest of the forum: do there exist tools for temporarily bonding metal objects which include the necessary protection from high voltage shock and arc flash? Do there exist tools to permit a sign worker to safely bond a sign without requiring electrical training?

-Jon

I'm with winnie- bonding may be called for.

I'm thinking the grounding mats and/or wrist straps used for electronics assembly may be the tool for "(safe) temporarily bonding". If I recall correctly, they have a 1meg resistor built in to dissipate static without the potential for large current flows.
http://www.desco.com/ViewProduct.aspx?pid=16475&h=983
here is link to a picture.

When I was a kid, we used to climb on everything around, including transmission line towers. These would deliver a nasty static shock sometimes- there was a guy who freaked out at it, and couldn't climb down for fear of the shock. Had to climb over and "ground" him with my hand. Told him to keep one hand on the metal all the way down and not come back up.

What I find odd is that the OP said it was worse in damp weather. I'd expect it to be worse in dry. Please let us know what results!

 

[ramsy]

I'm thinking the grounding mats and/or wrist straps used for electronics assembly may be the tool for "(safe) temporarily bonding". If I recall correctly, they have a 1meg resistor built in to dissipate static without the potential for large current flows.

We fought these wrist bands in one plant because hi-pot voltage was high enough for lethal let thru currents.

I'm not comfortable trusting my life to a resistor. Before experimenting with full OSHA fines and liabilities by issuing resistors or non-dielectric equip., not considered PPE, I would need to see it handle more than static, because an energized grounding circuit is not usually slowed by resistance, it tends to heat resistors at it burns thru them.