250.188(E)

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gregRooster

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Understanding 250.188(E)

Can anyone explain what the basis for 250.188(E) is?

Why would you not connect the grounding electrode of the portable system to the rest of the system? If you connect the portable device so that the equipment grounding conductor bonds to existing systems, then any lightning will find a path through the ECG from one electrode to the other. This seems totally counter to the rest of the code.

250.188(E) Isolation. The grounding electrode to which the portable or mobile equipment system neutral impedance is connected shall be isolated from and separated in the ground by at least 6.0 m (20 ft) from any other system or equipment grounding electrode, and there shall be no direct connection between the grounding electrodes, such as buried pipe and fence, and so forth.
 
gregRooster said:
... If you connect the portable device so that the equipment grounding conductor bonds to existing systems,
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Why would you do that? By accident?

then any lightning will find a path through the ECG from one electrode to the other. This seems totally counter to the rest of the code.
...
Click to expand...

FWIW I disagree that the rest of the code is written to avoid that problem with lightning or prohibits such problematic installations. I agree that what you describe is bad design, but the code allows it. In fact a few cycles back the code even required the bad design for solar arrays before cooler heads prevailed.
 
jaggedben said:
Why would you do that? By accident?



FWIW I disagree that the rest of the code is written to avoid that problem with lightning or prohibits such problematic installations. I agree that what you describe is bad design, but the code allows it. In fact a few cycles back the code even required the bad design for solar arrays before cooler heads prevailed.
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Regarding the 2nd paragraph, sure. There have been junk things. But, what is the purpose of 250.188(E)? How is this improving safety/ avoiding fires?
 
I was curious so I looked up the archival revision info at https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70. But all I can tell you is that this language was added to the 1975 NEC, and that it hasn't changed since. It was originally 250-154(e). The posted report on proposals for that year is apparently the proposed draft (presumeably the same as the text of the adopted code) and does not include the details of individual proposals and their substantiations like for most other years.
 
I think its because they are impedance grounded systems, not solidly grounded, and required to have the ground fault detection / monitoring relays, and if a bolted fault were to occur they dont want a difference in potential near the ground resistor.
 
gregRooster said:
Understanding 250.188(E)

Can anyone explain what the basis for 250.188(E) is?

Why would you not connect the grounding electrode of the portable system to the rest of the system? If you connect the portable device so that the equipment grounding conductor bonds to existing systems, then any lightning will find a path through the ECG from one electrode to the other. This seems totally counter to the rest of the code.

250.188(E) Isolation. The grounding electrode to which the portable or mobile equipment system neutral impedance is connected shall be isolated from and separated in the ground by at least 6.0 m (20 ft) from any other system or equipment grounding electrode, and there shall be no direct connection between the grounding electrodes, such as buried pipe and fence, and so forth.
Click to expand...

2023 NEC

It's not the function of the EGC and it is not a grounded conductor, Article 100 ,Grounding Conductor, Equipment (EGC).

See Article 100 for Grounded Solidly, Grounded Conductor, Grounded System, Impedance.

Yeah, just do what 250.88(E) Isolation.... It Says......

You're in Part X Grounding of Systems and Circuits of over 1000 Volts
250.186 (A) (4)

Review these sections for additional information.

TX+MASTER#4544
 
jaggedben said:
I was curious so I looked up the archival revision info at https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70. But all I can tell you is that this language was added to the 1975 NEC, and that it hasn't changed since. It was originally 250-154(e). The posted report on proposals for that year is apparently the proposed draft (presumeably the same as the text of the adopted code) and does not include the details of individual proposals and their substantiations like for most other years.
Click to expand...


I’m impressed the depth that you went. Thank you
 
tortuga said:
I think its because they are impedance grounded systems, not solidly grounded, and required to have the ground fault detection / monitoring relays, and if a bolted fault were to occur they dont want a difference in potential near the ground resistor.
Click to expand...
I’m not sold on that. They are often impedance grounded but not all; they aren’t required to be impedance grounded.

The logic also doesn't make sense to me. The grounding electrode is needed exactly as much with an impedance grounded system as solidly.
 
TX+ MASTER#4544 said:
2023 NEC

It's not the function of the EGC and it is not a grounded conductor, Article 100 ,Grounding Conductor, Equipment (EGC).

See Article 100 for Grounded Solidly, Grounded Conductor, Grounded System, Impedance.

Yeah, just do what 250.88(E) Isolation.... It Says......

You're in Part X Grounding of Systems and Circuits of over 1000 Volts
250.186 (A) (4)

Review these sections for additional information.

TX+MASTER#4544
Click to expand...
This feels like a combative and unhelpful comment. I didn’t post to show off. I posted because I don’t understand the logic for the code requirement.

250.186(A)(4) is just a reference to 250.187. Saying read this tells me nothing.

Maybe my question was unclear.
 
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