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Got one for you guys. Is there any reason why I should argue against putting ESD flooring inside an electrical room with 480/277V and 208/120V panels present?

I would gladly accept any NEC references and/or safety regulations to support the argument.

Reason why I am asking: Boss of cleanroom design firm is amazing at cleanroom design but is not well versed at basebuild and other engineering disciplines. I am the sole electrical person with two years experience so I want to find out if my reservations are right before arguing my position.

* Thank you everyone for your responses. Boss heard what I had to say and decided to stick with a sealed concrete slab in the electrical room.*

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    \$\begingroup\$ So what exactly is your position ? \$\endgroup\$ – Eugene Sh. Jun 21 '17 at 17:09
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    \$\begingroup\$ I am against it for safety reasons. I get the bad feeling vibe when I think about someone standing on a low resistance/ static dissipation floor right next to 480V panelboards. \$\endgroup\$ – J-InTheJ-Box Jun 21 '17 at 17:19
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    \$\begingroup\$ Well, I remember getting zaps from my anti-static grounded ankle strap when touching a non-grounded metal chassis of a badly wired mains-powered device... I am glad the resistance wasn't that low. \$\endgroup\$ – Eugene Sh. Jun 21 '17 at 17:23
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    \$\begingroup\$ I believe the dissapative range for ESD flooring is in the 1e6 to 1e9 ohm range. At 480 volts, that would equate to 480uA of current flow. Have to add in the resistance of the human, which would bring that value down. \$\endgroup\$ – Steve Jun 21 '17 at 17:57
  • \$\begingroup\$ You're right. The overall current between the voltage present and the total resistance to ground through the human body, shoes, and ESD flooring is quite low. A non-ESD floor would result in much lower overall current flowing through the body. But, as was asked then answered below, this electrical room is outside the cleanroom envelope and across the hall. \$\endgroup\$ – J-InTheJ-Box Jun 21 '17 at 18:29
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The question is not only one of limiting the current in this environment but also having a current limiting resistor with an appropriate voltage rating. The common voltage rating on ESD current limiting resistors is around 250 volts. Any mats that would be put in place would need to be certified for use in higher voltage environments.

You would also have to give thought to the test equipment that is used to ensure that the mats are still meeting specification. In this higher voltage environment, I would like to see something that is the equivalent of a HiPot test.

Here is one reference from an ESD mat manufacturer that specifically recommends against mats in environments where the voltage is > 250 volts. They also list several other references that may prove helpful in your investigation.

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  • \$\begingroup\$ Having worked at Jabil Electronics, I saw the need for having the higher rated voltage ESD flooring out on the production floor. However, this particular application that I am speaking of is inside an electrical room, outside the cleanroom envelope and with no reason for the researchers using the cleanroom to go inside the electrical room. The only people expected to go into the electrical room are maintenance staff and electricians. \$\endgroup\$ – J-InTheJ-Box Jun 21 '17 at 21:19
  • \$\begingroup\$ Sounds like you are thinking it through correctly. Best wishes in winning your case for the sake of everyone's safety. And you should save your company some capital expense at the same time. \$\endgroup\$ – Glenn W9IQ Jun 21 '17 at 21:22
  • \$\begingroup\$ Through researching this topic and having other conversations, I think i've ruled out safety as an issue. The currents are just too low (micro to nanoamps) to cause you any harm. That just leaves cost. \$\endgroup\$ – J-InTheJ-Box Jun 21 '17 at 22:53
  • \$\begingroup\$ Did you find mats with an appropriately voltage rated resistor? \$\endgroup\$ – Glenn W9IQ Jun 22 '17 at 0:54
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    \$\begingroup\$ I'm not going to look for ESD flooring to put in the electrical room. ESD flooring simply does not belong in there since this space is not attached to or accessed by the cleanroom. It will be a conventional slab on grade, typical electrical room powering ~800kVA worth of facility equipment, mechanical support equipment, RAHUs, big MAUs, and research laboratory tools and equipment. \$\endgroup\$ – J-InTheJ-Box Jun 22 '17 at 15:51
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Does anyone handle electronics in that room? If not, there is no need. Given valid the safety concerns you have (perhaps a short at the ESD dissipation resistor) and @Eugene Sh.'s observation, I agree with you.

Disclaimer: Not an electrician or an attorney.

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  • \$\begingroup\$ Thank you. This electrical room is outside the cleanroom envelope and across a non-esd flooring hallway. Since its purely an electrical room, there will be no reason to bring ESD sensitive materials into it. \$\endgroup\$ – J-InTheJ-Box Jun 21 '17 at 18:25

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