Alcohol Drying Room Grounding ?

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Davebones

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We had a area constructed last year that has some drying rooms for product . These were built and designed as Class 1 Div 2 area's . We dry product that contain alcohol in them . The rooms have a braided copper wire run around the wall's for doing any grounding with flexible ground straps .The contractor that installed this ran the braided copper to the building steel . The safety department had a audit done and they have asked us to verify the the grounding is less than 5 ohm's . They also said we should add a grounding rod for static . ( 1 ) Would a clamp-on be the best way to test this for less than 5 ohm's ? ( 2 ) If we added a ground rod in the room would this be a issue ? Since we are in a high lighting area that's why I ask about location . These room's are designed for the roof to blow out just incase so any opinion's on this is very much appreciated ...
 
what standard did they use to determine 5 Ohms was an appropriate value and just how is this to be measured?

I suspect that a ground rod will serve no real purpose.

OTOH, if they want to pay you to do stuff that serves no real purpose, as long as they pay, I guess it does not matter all that much in the grand scheme of things.
 
You should use a three point Fall of potential test to check your ground. If you don't have the equipment, you can hire any local NETA certified company, or most lightning protection contractors to do the test for you.
 
Strathead said:
You should use a three point Fall of potential test to check your ground. If you don't have the equipment, you can hire any local NETA certified company, or most lightning protection contractors to do the test for you.
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just curious. what standard says this is the appropriate test for whatever they are trying to accomplish?
 
petersonra said:
just curious. what standard says this is the appropriate test for whatever they are trying to accomplish?
Click to expand...

Not sure if this answers your question, but both Fluke and AEMC have extensive information on their web sites regarding "Fall of potential" testing. They also both have new methods of testing grounds that some agencies are accepting. I am pretty sure that NETA has published standards for testing ground potential It is just one of those things that you do. I don't know what standard says to use a voltmeter to check voltage, or a megohm meter to check insulation resistance, but I accept that is what they are for.
 
We had a client mixing oil based paint in 45 gallons drums in a room.He experienced several flashovers in the air to gound.Suspended in air above this mixing operation was installed a foil grounded system on a 3 foot grid . No problems after this install.:D
 
Chances are the building steel will have lower resistance to earth then any ground rod you add to this. Even if the building steel is not a qualifying grounding electrode per 250.52, it is likely still bonded to the electrical grounding system and has the grounding electrode system to lower it's resistance to earth. Your safety people need to focus more on elimination of potential places for static charges to build up then on resistance of intentional grounding leads. The whole area could be charged but it is when there is a discharge is when you have drastic consequences, keeping the entire area at one potential reduces the discharge possibilities, even if it is at a level above true ground. OTOH if you bring true ground into the space and don't properly reduce other potentials, you now have two areas of different potential within your area, build up enough of a charge and it may eventually arc across.

Is not exactly the same thing but is still some similarities to how we use equipotential bonding around swimming pools to reduce electric shock hazards. It doesn't matter so much what is at ground potential, what matters is difference in potential between objects within a specific vicinity.
 
Davebones said:
We had a area constructed last year that has some drying rooms for product . These were built and designed as Class 1 Div 2 area's . We dry product that contain alcohol in them . The rooms have a braided copper wire run around the wall's for doing any grounding with flexible ground straps .The contractor that installed this ran the braided copper to the building steel . The safety department had a audit done and they have asked us to verify the the grounding is less than 5 ohm's . They also said we should add a grounding rod for static . ( 1 ) Would a clamp-on be the best way to test this for less than 5 ohm's ? ( 2 ) If we added a ground rod in the room would this be a issue ? Since we are in a high lighting area that's why I ask about location . These room's are designed for the roof to blow out just incase so any opinion's on this is very much appreciated ...
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Is this a smokeless propellant facility?
 
Strathead said:
Not sure if this answers your question, but both Fluke and AEMC have extensive information on their web sites regarding "Fall of potential" testing. They also both have new methods of testing grounds that some agencies are accepting. I am pretty sure that NETA has published standards for testing ground potential It is just one of those things that you do. I don't know what standard says to use a voltmeter to check voltage, or a megohm meter to check insulation resistance, but I accept that is what they are for.
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The actual test procedure us not in dispute.

What I was asking is what standard says this is the appropriate test?

A blood test is indicated for certain things, for other things a urine test. I would be curious to know what standard says that the test you are proposing is appropriate.
 
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For a GES which includes building steel, water pipes, a CEE or other electrodes that are distributed over a wide area, the fall of potential test can very hard to do properly. The shape and gradient of the zones of influence around any single electrode will be distorted by all of the other nearby metal in the soil.
This can make it difficult to place your reference electrode far enough away for the fall of potential test to be valid.
Other techniques such as current injection via clamp are more suited for these cases, especially if you cannot disconnect the electrode under test from the rest of the GES temporarily.
 
petersonra said:
The actual test procedure us not in dispute.

What I was asking is what standard says this is the appropriate test?

A blood test is indicated for certain things, for other things a urine test. I would be curious to know what standard says that the test you are proposing is appropriate.
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I concur with this. On what basis was it determined that 5 ohms was necessary or, more importantly, adequate?

Several issues beyond the testing procedure of the grounding electrode system (GES) were raised in the OP alone:

  • Design of the GES
  • Bonding
  • Static
  • Lightning

I can make a few comments:

  • The description of bonding; i.e., "...grounding with flexible ground straps" is questionable in a Class I, Division 2 location. [See Section 501.30] NOTE: I haven't said it's wrong, but I'd sure like to know more about how the "ground straps" ("bonding straps", actually) are attached.
  • Appropriate static and lightning reference standards for classified locations are listed in Section 500.4(B) FPN/IN No. 3. I have found API RP 2003 to be pretty comprehensive.
 
The bonding straps that ground equipment and carts have 6 ft coiled grounding wire with a hand clamp on one end . The other end is bolted to the braided ground wire that is run around the room along the wall . As carts ( metal ) are rolled in with the product on them to dry they bond the cart with the clamp .
 
Davebones said:
The bonding straps that ground equipment and carts have 6 ft coiled grounding wire with a hand clamp on one end . The other end is bolted to the braided ground wire that is run around the room along the wall . As carts ( metal ) are rolled in with the product on them to dry they bond the cart with the clamp .
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This sounds an awful lot like a smokeless propellant drying house, except they used wooden trays. I have a vague recollection that Hercules had an internal spec for 5 ohms to ground for the floors and ancillary bonding jumpers for equipment.
 
Davebones said:
The bonding straps that ground equipment and carts have 6 ft coiled grounding wire with a hand clamp on one end . The other end is bolted to the braided ground wire that is run around the room along the wall . As carts ( metal ) are rolled in with the product on them to dry they bond the cart with the clamp .
Click to expand...
So - how would 5 ohms to ground change anything? Again, it sounds like someone is thinking, "Since 25 ohms to ground is good, 5 must be better." with no actual basis for it. There's actually no basis for 25 ohms to ground either other than it's been in the NEC a very long time with little known substantiation.

I don't know the lightning situation but a specific ground resistance isn't even mentioned in the main text of NFPA 780. Even Annex B Principles of Lightning Protection, Section B.3.5 only states, "Low resistance is desirable, but not essential ..."

With regard to static, unless there has already been evidence of discharges, I suspect there's no problem there either.
 
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