arre ground required on old commercial conduit?

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pvc in decks

pvc in decks

Working in a service fashion for many years pvc in the deck has caused some interesting issues.
One bank customer had a problem with movement in their crt computer screens at certain work locations. After I investigated the problem I noticed the problems were right in line where the padmount service equipment and the main electric room.
The service was run in the deck and the high current of the building load was causing the computer screens to distort. I suggested a farraday room until they saw the price and it all got shot down.
Cheaper to move the offices
 
Pvc in deck

Pvc in deck

Annother issue was a very large contractor in my area who is an EE from MIT was going to a job he built to get a check.
While walking thru the rain in some very expensive Italian leather shoes he reached for the front door and found himself recieving a shock from which he could not let go.
Upon further investigation the door installer shot a pin into the threshold which pierced an under slab pvc pipe and energized the entire doorframe to the building entrance.
Grounding is very important to me although I always get a lot of heat for saying that appologies in advance.
 
quogueelectric said:
What if it went into the deck and changed to pvc in the deck?
Click to expand...
I knew sooner or later, deck as in earth would be confused with deck as in wood structure in the back yard. :roll:
 
deck

deck

LarryFine said:
I knew sooner or later, deck as in earth would be confused with deck as in wood structure in the back yard. :roll:
Click to expand...
I am not confused. I mean deck as in concrete deck. that is not to say I dont like decks <rimjoist please> I have a 1 man auger for digging deck footings/foundations 8"x36deep to get below frost line
 
Someone mentioned job specs earlier. In my area it is often spec'd out to pull a grounding conductor in all raceways. By now it is common practice. We always pull a EGC. I do bet that a guy could save on materials cost by not pulling EGCs on smaller demo/remodels or any unspec'd jobs.

As someone else already aluded to, however. A raceway's suitability as a ground is only as good as the craftman installing it. I've heard about ground fault which did not immediately trip the breaker. I was told that along the exposed sections of emt you could see arcing at the couplings. That would be spooky.
 
Quogueelectric,
The distortion in the monitor you mentioned would have been due to the magnetic field from the service cable as you suspected. However, a faraday cage would have had no effect on the field. That is for RF and electric fields. 60 Hz Magnetic fields go right thru.

There are two possibilities: The high magnetic field could have been from net current on the service cable due to some neutral going back to the Tfrmr on a water pipe to another service. In that case the solution is to block that current path and end the net current in the service cable.

The other possibility (less likely) is that it is just a high load in very close proximity to the monitor. In that case one could move the monitor a matter of inches. Otherwise a wrap of Mu metal around the cable would reduce it enough. But this cause is unlikely.

Too bad if they went to the expense of moving equipment out.

Karl
 
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