Parking Lot Lights Ground Fault

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I've been looking at a nightmare.
But have a question based on the fact as Mike Holt has informed us that current only returns back to its source......hold onto this thought.

Here's the situation..... There is a 480 delta to 208 Y transformer connected backwards ( 120/208 volt service to building) which is being used to step-up voltage out to a parking lot lighting.
Now since there is no place on the 480 volt side of transformer to connect ground ( I guess one could say ~ isolated supply?~ ) would a person receive a shock at all if a wire should fault to pole? Cause where would the current go ? Nowhere, because there is no return path back to transformer?
So should Mike show an example of such a set-up?
 
mopowr steve said:
I've been looking at a nightmare.
But have a question based on the fact as Mike Holt has informed us that current only returns back to its source......hold onto this thought.

Here's the situation..... There is a 480 delta to 208 Y transformer connected backwards ( 120/208 volt service to building) which is being used to step-up voltage out to a parking lot lighting.
Now since there is no place on the 480 volt side of transformer to connect ground ( I guess one could say ~ isolated supply?~ ) would a person receive a shock at all if a wire should fault to pole? Cause where would the current go ? Nowhere, because there is no return path back to transformer?
So should Mike show an example of such a set-up?
Click to expand...

Are you saying this thread is a nightmare?

There are places to connect ground to the delta. One of which would be one of the lines. This is called a corner grounded delta. Folks are not getting shocked by the corner grounded delta. There is your proof.

Ungrounded systems are safer for personnel but have issues with high frequency transient overvoltage. Or so I've heard...
 
No the tread is not what I'm referring to.

As I was saying, by not grounding the secondary of this transformer (corner ground or otherwise) in theory a person touching a pole that has one of the lines feeding it shorted to pole should not receive a shock...... Correct?

Yet, a number of years ago I did get a hell of a jolt while changing a lamp with one hand and accidentally touched the shell of lamp and had the lens/cover in the other.
 
mopowr steve said:
No the tread is not what I'm referring to.
Click to expand...
:thumbsup:

mopowr steve said:
As I was saying, by not grounding the secondary of this transformer (corner ground or otherwise) in theory a person touching a pole that has one of the lines feeding it shorted to pole should not receive a shock...... Correct?
Click to expand...

Yes that is my understanding. The first line to pole short is "free". With only one line shorted the system is now corner grounded. I think there would be some charging current which would develop a voltage. If one line is shorted to the pole and then another line becomes shorted to the pole you would then have a short circuit and fault current would flow until the OCPD clears the fault.

mopowr steve said:
Yet, a number of years ago I did get a hell of a jolt while changing a lamp with one hand and accidentally touched the shell of lamp and had the lens/cover in the other.
Click to expand...

What type of system was this? was the lens cover tethered to the pole by a conductive material?
 
mopowr steve said:
No the tread is not what I'm referring to.

As I was saying, by not grounding the secondary of this transformer (corner ground or otherwise) in theory a person touching a pole that has one of the lines feeding it shorted to pole should not receive a shock...... Correct?

Yet, a number of years ago I did get a hell of a jolt while changing a lamp with one hand and accidentally touched the shell of lamp and had the lens/cover in the other.
Click to expand...

You can't have both "not grounded" and "corner grounded" in the same system:?

Add: a fault of one phase conductor to ground on a system intended to be ungrounded now essentially becomes a grounded conductor until that fault is fixed.
 
mopowr steve said:
No the tread is not what I'm referring to.

As I was saying, by not grounding the secondary of this transformer (corner ground or otherwise) in theory a person touching a pole that has one of the lines feeding it shorted to pole should not receive a shock...... Correct?

Yet, a number of years ago I did get a hell of a jolt while changing a lamp with one hand and accidentally touched the shell of lamp and had the lens/cover in the other.
Click to expand...
In the real world there is no such thing as an ungrounded system. The so called ungrounded system is really a capacitive grounded system. Unless the system is very small the capacitance current is more than enough to cause a fatal shock if you are "grounded" and touch one of the circuit conductors.
 
don_resqcapt19 said:
In the real world there is no such thing as an ungrounded system. The so called ungrounded system is really a capacitive grounded system. Unless the system is very small the capacitance current is more than enough to cause a fatal shock if you are "grounded" and touch one of the circuit conductors.
Click to expand...

Thanks again for your perspective Don. It is very much appreciated. Could you explain more on this subject?

I think what you are saying is that if there is no intentional or unintentional bond to earth ground there would still exist a voltage potential to earth.

Is this because one could consider the earth as one electrode of a capacitor with the other electrode being an ungrounded conductor of the ungrounded system? Would the circuit construction and length affect this?
 
MD84 said:
I understand that the lighting circuit is typical and meets code. The client asked so I feel that they should be given an accurate answer. My original response was accurate however I did not tell them that there is the potential for a hazardous voltage during a fault.
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Understood.


Just because it has been done a certain way in the past does not prohibit us from improving methods in the future. I think that we have a responsibility as those installing and servicing electrical equipment.
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For sure, on the other hand you are not breaking any new ground here. This issue has been around, it has not been something hidden away that countless others have been ignoring.

It sounds like the installation you are dealing with does not meet current code as far as EGC size. If I was to make any changes to this circuit I would start with that. Bring the circuit into current NEC compliance and go from there if need be. Just my personal opinion. :)
 
kwired said:
Also remember if the pole has a good bond to the EGC and there is a fault to the pole, electrically the pole is approximately at mid point of the voltage drop in the faulted circuit path, so touch voltage on that pole is reduced to around half of normal line to ground operating voltage also lessening the severity of what shock might be experienced, the pole/base probably has reasonable grounding electrode properties or even a ground rod - which doesn't automatically bleed off potential voltage, but will further mitigate some of the touch potential, so if you have a 120 volt circuit fault to the pole, around 60 volts is the mid point, then maybe you get the electrode to raise the potential where you are standing another 10-30 volts and the shock you receive maybe only has 30 to 50 volts behind it instead of full 120. Now at this point unless you are standing there barefoot or are otherwise contacting something at true ground potential, you probably have enough other insulation that you aren't even exposed to a significant enough voltage potential to feel.
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That 60V reduction from 120V is due to voltage drop in the phase wire. Further reduction of the fault voltage may be possible at the pole end, depending on the ratio of pole end ground resistance to the POCO supply transfomer neutral ground resistance.
 
Sahib said:
That 60V reduction from 120V is due to voltage drop in the phase wire. Further reduction of the fault voltage may be possible at the pole end, depending on the ratio of pole end ground resistance to the POCO supply transfomer neutral ground resistance.
Click to expand...

That 50% drop occurs at the mid point of the total impedance of the complete circuit. So if you had same size and length ungrounded conductor as the EGC and no other paths then your fault point is going to be at 50% of the applied voltage. Change the size of either conductor or add multiple return paths and you change how much impedance is on each side of the fault and the voltage at the fault point will vary accordingly.
 
MD84 said:
Is this because one could consider the earth as one electrode of a capacitor with the other electrode being an ungrounded conductor of the ungrounded system? Would the circuit construction and length affect this?
Click to expand...

Yes, it all comes down to how much capacitance (storage ability) the capacitor has as far as how much current will flow when you place a conductive path across the capacitor electrodes.
 
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