GEC Debate: Valet Parking Booth

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brother

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I have a question about the GROUNDING ELECTRODE CONDUCTOR. There's this parking booth where they take the money/tickets etc.. that is out side and technically it's not 'attached' to the main building. There was a run a feeder to the subpanel in the booth. Subpanel feeds several circuits.

This is an older booth, (I think about 5 to 7 years). It was my understanding that a GEC (2 ground rods) would 'technically' still been required. The 2008 NEC 250.32 is what I see here (I dont have my older code books in front of me). Also there are other 'metal' piping between this booth and the main building structure because they ran other circuits just outside of it to the main walkway close to it.

Since its out in the opening I can see lighting hitting it, (even though its 1 in a million). so my question is was a GEC required for this booth??
 
brother said:
Since its out in the opening I can see lighting hitting it, (even though its 1 in a million). so my question is was a GEC required for this booth??
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I say yes - lightning or not... IMO it is more about grounded surfaces and equipment being closer to the same potential than the earth around them.
 
e57 said:
... IMO it is more about grounded surfaces and equipment being closer to the same potential than the earth around them.
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But it just doesn't work that way. If you are touching the earth 3' away from the grounding electrode and also touching a grounded surface that is energized by an uncleared fault, you will be subjected to about 85% of the fault voltage.
 
brother said:
I have a question about the GROUNDING ELECTRODE CONDUCTOR. There's this parking booth where they take the money/tickets etc.. that is out side and technically it's not 'attached' to the main building. There was a run a feeder to the subpanel in the booth. Subpanel feeds several circuits.

This is an older booth, (I think about 5 to 7 years). It was my understanding that a GEC (2 ground rods) would 'technically' still been required. The 2008 NEC 250.32 is what I see here (I dont have my older code books in front of me). Also there are other 'metal' piping between this booth and the main building structure because they ran other circuits just outside of it to the main walkway close to it.

Since its out in the opening I can see lighting hitting it, (even though its 1 in a million). so my question is was a GEC required for this booth??
Click to expand...

Are the metal piping systems underground?
 
don_resqcapt19 said:
But it just doesn't work that way. If you are touching the earth 3' away from the grounding electrode and also touching a grounded surface that is energized by an uncleared fault, you will be subjected to about 85% of the fault voltage.
Click to expand...

How would you get shocked if it is grounded? Maybe if you were rolling on the ground laughing at the last guy's deer antler shaped conduit run and touched the building that had a fault you could get shocked.
 
220wire said:
How would you get shocked if it is grounded? Maybe if you were rolling on the ground laughing at the last guy's deer antler shaped conduit run and touched the building that had a fault you could get shocked.
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Look at this illustration for an example.

touch.gif


Roger
 
Where is the GEC in the picture? Don't see one. Maybe if the contractor wasn't cheap and in a hurry that wouldn't happen. I understand even with a GEC electrocution still could happen, but I would say the potential for shock is reduced. BTW the guy in the pic shouldn't be working on an energized circuit. He might be trying to steal the wire in that case probably deserves the shock:D
 
220wire said:
Where is the GEC in the picture? Don't see one. Maybe if the contractor wasn't cheap and in a hurry that wouldn't happen. I understand even with a GEC electrocution still could happen, but I would say the potential for shock is reduced. BTW the guy in the pic shouldn't be working on an energized circuit. He might be trying to steal the wire in that case probably deserves the shock:D
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The GEC is connected to the rod, what do you call a GEC? I think you are confusing an EGC with a GEC.

An EGC (even if it were metalic conduit or tubing) would in fact change the outcome shown in the illustration

Roger
 
Lighting will strike a building or booth with no electrical equipment, regardless if its a 40 ampere or 400, or 4,000 ampere feeder or service.
The NEC requires a GES for every building served by a feeder. Its a common mistake (I've done it) to run a four wire feeder with no GES.
But this example shows why we get confused on grounding and bonding.
 
roger said:
The GEC is connected to the rod, what do you call a GEC? I think you are confusing an EGC with a GEC.

An EGC (even if it were metalic conduit or tubing) would in fact change the outcome shown in the illustration

Roger
Click to expand...

EGC - bonding jumper. I meant the green wire
 
tom baker said:
Lighting will strike a building or booth with no electrical equipment, regardless if its a 40 ampere or 400, or 4,000 ampere feeder or service.
The NEC requires a GES for every building served by a feeder. Its a common mistake (I've done it) to run a four wire feeder with no GES.
But this example shows why we get confused on grounding and bonding.
Click to expand...

Does any one know when this was first required. Seeing that this is a 'booth' its not really a building in my 'personal' definition. its more a 'structure' ;) which is covered by NEC 2008 250.32.
 
don_resqcapt19 said:
But it just doesn't work that way. If you are touching the earth 3' away from the grounding electrode and also touching a grounded surface that is energized by an uncleared fault, you will be subjected to about 85% of the fault voltage.
Click to expand...
I said - "CLOSER" - not the same.... ;) Nor did I mention a fault condition. What I was eluding to was potential reduction for a EGC grounded remotely from the out-building.

Anyway - imagine if this rod were 300'+ away from him... At the service only...
touch.gif


If they were no purpose for it - why would we do it? Why bother doing it at services for that matter?
 
e57 said:
I said - "CLOSER" - not the same.... ;) Nor did I mention a fault condition. What I was eluding to was potential reduction for a EGC grounded remotely from the out-building.

Anyway - imagine if this rod were 300'+ away from him... At the service only...
touch.gif


If they were no purpose for it - why would we do it? Why bother doing it at services for that matter?
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If the only rod was 300 feet away the voltage would increase from 82 to 120...is that really a difference?

As far as the purpose, there is little purpose for grounding electrodes other than some protection from lighting or contact with a higher voltage system.

The only thing that really provides shock protection is bonding (EGC) and that only works to clear the fault quickly. Even with a correctly installed EGC, it is possible to have fatal voltages to ground from the faulted equipment, and this voltage will remain until the OCPD opens the circuit.
 
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. 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... And (for those who don't know already) the further you are from the MBJ the voltage difference will increase between the grounded conductor and the EGC due to load, voltage drop, and induced voltage, just as well as the difference between the EGC and the actual earth - which is why each structure has a local electrode connected to the EGC in the very least - the way I understand it... Otherwise, a single rod at a pole/pad mounted transformer a mile away would surfice... ;)

(Previous codes like the '05 NEC 250.32(B)2 allowed no EGC with the feeder and a second MBJ to the required electrode system, this would become the connection point for all EGC's in that structure. Much like a new service. )
 
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