Video: Are You Moving Your Electronic Parts Safely?
August 6, 2021
A typical conductive caster measures approximately 10 cm in diameter but has a contact area of only 1 square cm. To put this in perspective, the NFPA probe used to measure the resistance from the surface of an ESD floor to ground has a contact area of 31 square centimeters. The distance between conductive particles used in a typical chip technology ESD floor can measure from .5 cm up to 10 cm with an average of 2 to 5 cm. Therefore ANSI/ESD STM 7.1 resistance testing will not predict whether a particular floor will consistently provide reliable electrical contact between casters and flooring. The only way to make a determination is by conducting a statistically valid sampling of resistance measurements using the carts, casters and flooring that will be purchased by the facility. This should be done before any flooring is ordered. Once a floor has been installed it is too late to address the problem. Most flooring manufacturers do not provide data or warranties involving caster contact resistance.
In this video, Dave explains why caster contact can be the achilles heel of ESD flooring and how to mitigate this risk.
Standard ESD Resistance Tests Do Not Fully Evaluate a Floor’s Suitability for Grounding Carts, Chairs, and Mobile Workstations
What’s the purpose of installing an ESD floor? The most common answer to this question is “we need ESD flooring to prevent static charges on mobile personnel when they handle static sensitive parts and systems.” In other words, we need the effectiveness of a wrist strap, but we don’t want to deal with the restrictions of wires and cords.
While this answer highlights a key attribute of a properly functioning ESD floor, it sets the bar very low. It also short sells the many advantages an ESD floor actually offers. Like every other static mitigation component, ESD flooring is only one piece of a larger comprehensive system that keeps all parts, machines, tools, packaging, work surfaces, and personnel at the same potential.
Hi, I’m Dave from StaticWorx.
You recognize this? It’s the five pound probe we use to test static-control floors and other things. The reason we’re talking about it right now is when we evaluate a static-control floor what we normally look at, if you talk to most people is they want to know what the electrical resistance is from one point to another, they want to know what the electrical resistance is from point to ground. They want to know what the electrical resistance is from a person to ground, and then they want to know how much voltage the floor can generate when it’s walked on. Does that cover everything? Far from it, and unfortunately the more people I’ve talked to over the last year, I’ve come to realize no one is checking their floors to find out the most important thing: is the product grounded? Are the ESD chairs that you might be using, are they grounded? Are your carts grounded? Carts have conductive wheels.
So we’re using a five pound weight with two and a half inches in diameter of contact area. Take a look at this caster, look how a little contact area it actually has. I put a dime on this caster, I’m only actually touching roughly half the dime.
So over the years, different technologies in ESD flooring, have evolved. I’m going to show you just a few of them because some of them were our floors, some of them were other people’s floors, but the understanding was as long as we grounded people, as long as their heel strap would make contact with conductive points on the floor, we were good to go, as long as the floor did not generate charge on a person who may walk on that floor.
Look at this floor, this floor the only thing that’s conductive here are these chips. I can put a dime and not touch a chip, I can put two dimes, I could probably put three dimes, if I happened to have another one, but look at my caster, I can put my caster on there and it’s not touching any conductive material. So if I’m relying on that floor to ground a chair, to ground that wire cart with the trays on it, with the moving circuit boards, this isn’t going to get it done, and you’re not going to know that because you didn’t test for it.
So this kind of a floor evolved to this type of a floor. It’s a little more attractive, the speckles are smaller, but I can still put a dime on there in certain spots and I have to play with it, but I can find spots where there’s no conductive points. When we tested this technology, we found that it failed 84% of the time, that means with the carts that we tested it with 84% of the time, it wasn’t doing what it was supposed to do, at least with one caster. That led to looking at the old technology, which is, also a very reliable technology of veins. I can put a dime any place on these floors with the veins, and it’s always going to make contact with conductive materials.
But if I want to use chips instead of veins, I can now do that. This new version of GroundLock, it’s a interlocking floor, there is no way I can put anything on here that’s the size of the dime without touching several conductive points. So if you want to look at this, maybe just from a statistical perspective, think of the floor as it’s only doing 50% of its job. If you’re worried about grounding people and keeping people from charging, the other 50% of the job of a floor is to allow you the mobility to be able to move products around on carts, maybe on automatic guided vehicles, and different types of material handling trays that the floor becomes the ground. So you need to know whether that floor is doing what it’s supposed to do.
So there’s a couple of ways you can do this. One of them is you can repeat the test that we did. You can read the article, we just published in In Compliance. We can loan you meters, if you’re working with us with our floors, we can tell you how to do these tests, but they’re required, you just have to look a little bit further, look at the ANSI 4.1 requirements. You need the floor and whatever fixtures are on it, to provide a path to a groundable point, that’s less than 10 to the ninth (10E9). Some of these things I just showed you, I’m not getting into the meter and all that, they don’t do that. So call us, have us send you a sample, do a mock-up, get your meters out, but start asking more questions than whether or not the floor is just grounding the people in my building.
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