Why two grounding electrodes

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alixenos

alixenos

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Florida
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Electrical Design Engineer
Hello,

I'm trying to understand article 250 ( Grounding and Bonding), and it has an exhibit similar to the following.

1703097926666.png

My question is why there are two grounding electrodes? one at the service and the other at the equipment? why can't we just do away with the grounding electrode at the equipment?

Thank you
 
For clarity which are you calling the service and which are you calling the equipment? I only see the utility transformer and the service disconnect.
 
Im sorry, by the service I meant the utility. Yes I'm questioning the two grounding electrodes in the utility transformer and the service disconnect.
 
It's because the utility transformer and the service disconnect are in separate locations. Earth does not count as an interconnection, so it's not considered to be a parallel pathway.

If they were adjacent, only one of them would be needed, and they could share one electrode system.
 
LarryFine said:
It's because the utility transformer and the service disconnect are in separate locations. Earth does not count as an interconnection, so it's not considered to be a parallel pathway.

If they were adjacent, only one of them would be needed, and they could share one electrode system.
Click to expand...
Thank you, that makes sense. another question please.

Grounding in the NEC is defined as " intentionally connecting a current-carrying conductor to the ground"

For single phase 3 wire, we intentionally connect the neutral to the ground as shown in the picture above.

How about if we have a delta 3phase system that does not have a neutral, How do we provide grounding to such system?
 
alixenos said:
Thank you, that makes sense. another question please.

Grounding in the NEC is defined as " intentionally connecting a current-carrying conductor to the ground"

For single phase 3 wire, we intentionally connect the neutral to the ground as shown in the picture above.

How about if we have a delta 3phase system that does not have a neutral, How do we provide grounding to such system?
Click to expand...
That depends on if you have a grounded system or an ungrounded system.
 
For residential, the utility's pole transformers have a grounded jumper between the primary and secondary windings.
 
roger said:
Which has no bearing on the NEC side of things.
Click to expand...

As today’s electrical loads continue to escalate, more
current is forced into and over the earth. The question
electrical engineers and the public must answer is what is the
acceptable safe level, if any, of the passage of uncontrolled
flow of electrical current over the earth and into our homes,
office buildings and industrial facilities.

In my opinion, the NEC has gotten into the discussion with requiring a copper mesh must now be placed around swimming pools to help neutralize the gradients currents pumped into the ground from each power pole transformer.
 
alixenos said:
How about if we have a delta 3phase system that does not have a neutral, How do we provide grounding to such system?
Click to expand...
Either corner-grounding, which is basically grounding and bonding one phase as you would a neutral.

Or providing ground-detection, which basically alerts you if a phase accidentally becomes grounded.
 
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