GEC Debate: Valet Parking Booth

[iwire]

My understanding is - that apart from lightning - which some areas have little or none of, not everywhere is Florida - is to bring conductive surfaces of electrical apparatus 'closer' to the same potential.

That may have been the intent but as the grapic shows that is really not what happens.

Having a grounded conductor would be difficult without ground... (Earth) Otherwise it would be a floating neutral... And since we have a MBJ at the service, the EGC would also be floating (potential wise) and could be a shock hazard due to the difference between it and the ground (earth) you're standing on.

True, but the fact remains with a big enough 'push' the EGC and the neutral can be at a fatal potential to earth only a short distance from the electrode.


Connecting to earth is a lot like connecting to a large resister and at any distance from the connection you will have a difference of potential. (Of course an EGC is also a resister, but not nearly as much as the connection to dirt.)

 

[e57]

Well put Bob...

Then why have an electrode in the first place - personally I would love to cease the practice of pounding 8-10' of copper clad steel into rocks... Skip the water ground or bond, and the Ufer too. For that mater - why have a ground at all, sans an electrode to connect them to? But we would have to call it something else - like "that sometimes external - usually not current carrying - extension of the neutral conductor" - or something to that effect...

Anyway I found an article that puts context to the picture being batted around here...

 

[don_resqcapt19]

My understanding is - that apart from lightning - which some areas have little or none of, not everywhere is Florida - is to bring conductive surfaces of electrical apparatus 'closer' to the same potential. ...

Grounding won't bring the conductive surfaces of electrical equipment closer to the same potential, but bonding will.
As far as reducing the potential between the earth and the conductive surfaces by the use of grounding electrodes, how would that work? Where would the voltage go?

 

[220wire]

I had an experience as an apprentice with EGC not clearing a fault. Had an office building with about 10 parking lot lights on concrete bases and a water fountiain in the middle. During the open house the architect's kid was playing in the fountain and got shocked. Not bad but a tingle could be felt. All of the circuts went into a pvc junction box in a vault that housed the pump controls and fiber optic lighting. The guy who went back and fixed it said that it was a wire that got pinched in between the pole and concrete base when we set the poles. I had always figured an EGC would have prevented that, but apparently the fountain was a much better path.

 

[iwire]

I had always figured an EGC would have prevented that, but apparently the fountain was a much better path.

What do you mean?

 

[220wire]

What do you mean?

That it wouldn't have happened. The EGC would have caused high impedance and tripped the breaker. Instead since we tied all the grounds together in the jbox it heated the fountain up finding a better way to earth. Now lay it on me and tell me what a moron I am now cause you wouldnt have said "what do you mean" if you wern't going to tell me I am wrong.

 

[e57]

I had always figured an EGC would have prevented that, but apparently the fountain was a much better path.

The fault will take ALL AVAILABLE paths in part to each but never in whole - unless there is one only. This is the "path of least resistance" myth...

A really long or small set of circuit and EGC's may not clear a fault in a timely manner - or at all, depending on length, conductor size and location of the fault from the OCP. But then again in this case the fault may not be returning to the EGC at all.

Also - Maybe the conductive energized surface the kid got shocked by was isolated from the EGC and the kid either completed the only path to it, or got shocked by completeing the only path from the fault to earth itself.

And the fountain should have had a GFCI - but that too may not have tripped or protected against shock for a number of reasons.

 

[roger]

finding a better way to earth. Now lay it on me and tell me what a moron I am now cause you wouldnt have said "what do you mean" if you wern't going to tell me I am wrong.

Well I don't believe you are a moron but you are believing a few myths and I think the biggest one is that you think current is seeking earth, this is not true, it seeks all available paths back to it's source.

Roger