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What is proper grounding for a hazardous goods storage area?

How to properly ground a hazardous material storeroom that has two lights?

Mel’s work plan is as follows:

  1. Mount 20mm steel conduit  horizontally onto the room concrete wall.
  2. Run an earthing wire from the room lights and mount onto the steel conduit.
  3. Mount an earthing wire with an alligator clip onto the steel conduit for earthing each drum when they are in use.

Hi Mel, thank you for your excellent question regarding proper grounding for hazardous material storage.  Properly bonding metallic components in hazardous storage areas is a vital requirement to ensure proper safety. Differences in potential and static electricity can cause sparks and/or hazardous currents to flow through combustible materials, resulting in fire and/or explosion. It sounds like your project has requirements to eliminate these hazards.

When discussing static control it is important that one understand the difference between “Bonding” and “Grounding” (also known as Earthing), as you will need to do both in order to provide proper protection.  Our concern is that simply pulling a ground wire from the existing lights is probably inadequate, and could quite possibly have negative consequences.  If some component on the same circuit as the lights were to fault, you could end up forcing hazardous current into your combustible storage room.  That would be very bad indeed.

As engineers, we become very concerned about answering questions along these lines as there are simply too many issues to handle via email.  Ensuring that you have adequate and effective grounding, that you do not have isolated grounding, and that you have proper bonding between components, is trickier than it you may think.  Also, providing a low resistance-to-ground electrode, generally requires on-site testing and computer modeling.

We would highly encourage you to contact an expert in this field to review your project plan.  If not us, please consult with someone who understands the nuances of grounding and bonding in hazardous storage areas.  Also, please keep in mind that filling and un-filling of combustible chemicals may have additional grounding and bonding requirements.

We hope you find this information valuable and thank you once again for considering E&S Grounding Solutions.

Best regards,
The E&S Grounding Solutions Engineering Team

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3 Responses

  1. Hi Lou,

    Thanks for your posting. I couldn’t find NEC Table 260 either. Can you tell me where it is referenced?

    The current National Electric Code is the 2011 version, although most cities & states are still enforcing the 2005 and/or 2008 versions. The 2002, 1999, 1996, 1993, 1990, and older versions of the code are primarily out of date. Although it is possible that some cities are still using the 2002 version. I really couldn’t speak to what was allowed in the older codes, as my memory is not that good, but plain iron rods would be a code violation under the latest standards that require grounding electrodes to have corrosion protection (typically a thin copper coating). I also recommend 10-ft rods, as they have a sphere-of-influence nearly twice that of an 8-ft rod, and they more easily meet burial requirements under the NEC.

    Also remember that all ground electrodes, including static electrodes, must be brought to the same potential within the electrical system. Isolated ground rods are a violation of the NEC.

    Have you looked up NFPA 77? It is a much better guide for static control and bonding in Hazardous areas.

  2. Lou

    Thanks for this info. It was helpful, except the part the ref. to NEC Table 260, etc. I could not locate the info, and on an older NEC (dated 1992) it stated to use an 8 foot deep, no less than 5/8″ diameter iron rod. So I am assuming this would certainly take care of any static electrictity, etc. on a metal hazmat storage shed that has two lamps, etc. No info on clamps or welding and of what size branded cable is recommended, to the grounding rod. But how nice it would have been in the NEC if it was just a bit more specific, eg. for all Class 1 Div 2 HazMat metal storage sheds, ……..etc. etc. But thanks for what you did provide. It was a bit more than what I had.

    Lou

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