mixing grounds

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malachi constant

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I have a project where a Motorola R56 telecommunications grounding system is being installed under a raised floor. The telecommunication grounding conductors extending to the underfloor ground busses are installed as bare. The Owner's grounding consultant allowed this on condition that the conductor was taped as it crossed over various EMT conduits to prevent the telecommunications and normal equipment grounding systems from touching.

It was pointed out that both the bare telecommunication grounds and the EMT conduits are touching the bare concrete floor. This is an upper floor, not at grade. Do we have an issue here?

Thanks!
 
Concrete in of itself is not a conductor so I would not fret that. I wont go into commenting on the "Tape" situation of the conductors as they cross the EMT since I will keep my opinion on that to myself. But in asking directly if having EMT and a bare conductor touching the same concrete flooring...I do not see this as a concern in respect to the question you are asking. Others may chime in differently.
 
I don't know a thing about Motorola R56 telecommunications grounding systems but it seems to me if incidental contact with other grounded items is a problem you would think an insulated conductor would have been specified. :huh:
 
iwire said:
I don't know a thing about Motorola R56 telecommunications grounding systems but it seems to me if incidental contact with other grounded items is a problem you would think an insulated conductor would have been specified. :huh:
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Oh I so agree with that reasoning....Indeed !

And that SCARES ME !:angel:
 
iwire said:
I don't know a thing about Motorola R56 telecommunications grounding systems but it seems to me if incidental contact with other grounded items is a problem you would think an insulated conductor would have been specified. :huh:
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When you boil it all down the spec is basically bonding everything within a stones throw away that is metal back to a single point and any metal to metal connections that are steel are not good enough; sometimes you need a home run other times you can use copper jumpers. It is a lot of of work but that's not real the problem meeting the spec.

The problem is dealing with the particular engineer or tech on any one project. If you happen to point out a particular incongruity in his reasoning the first response you will get is a bunch of technobabble. Keep it up and you get whisked away to a far off island when no one is looking.

Where's Dave?
He was just here a second ago.
You guys take a break, I need to make a few phone calls.....
 
even insulated wires sitting on metal conduit can cause the insulation to wear through over time. its looks like its at rest, but its moving. just gravity can squish out insulation over time. the psi can be rather high with say an insulated 12awg running perpendicular and on top of say 1/2" rmc. tape?? i'd say if there is concern you would place fiberglass sheath pieces on the gnd wire where it crosses rmc, and a piece of 1/8" thick foam/rubber tape over the rmc at touch point.

gnd loops are issue in automotive systems, this same problem can occur in what you are working with.

i guess best solution is, insulated gnd wire and dont let it sit on any metal, be it rmc or other.
 
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FionaZuppa said:
even insulated wires sitting on metal conduit can cause the insulation to wear through over time.
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Can happen but rarely happens with 'live' wires, I doubt it happens much at all with a grounding conductor alone.


FionaZuppa said:
i'd say if there is concern you would place fiberglass sheath pieces on the gnd wire where it crosses rmc, and a piece of 1/8" thick foam/rubber tape over the rmc at touch point.
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I would be ashamed to do such DIY looking work. :ashamed1:
 
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iwire said:
Can happen but rarely happens with 'live' wires, I doubt it happens much at all with a grounding conductor alone.




I would be ashamed to do such DIY looking work. :ashamed1:
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its under a floor. practicality, functionality, and looks are varying factors in any job. it would be very DIY'ish, hence why i suggested just route insulated gnd so it doesnt sit on anything, or just use insulated wire and say its as good as tape. if its a computer floor where floor panels are lifted and people get in there and move stuff around, i'll bet ya over time insulated wire will wear through...... or maybe install mini-ladder bridges over every conduit where the gnd might lay on :blink:
 
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