new definition of grounded

[jwelectric]

I declare either I am blind or have no reading comprehension at all as I can not see where there is a conflict with 250.20 and 250.34

II. System Grounding
250.20 Alternating-Current Systems to Be Grounded.
Alternating-current systems shall be grounded as provided for in 250.20(A), (B), (C), or (D).
Other systems shall be permitted to be grounded.
If such systems are grounded, they shall comply with the applicable provisions of this article.

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:

Where is the conflict?
If there is a conflict could someone please take the time to point it out?

 

[wwhitney]

Based on the definition of "premises wiring" a cord plugged into the receptacle on the generator is premises wiring.

How do you reach this conclusion? I don't really see it, perhaps I'm missing something.

From my reading of the 2008 definition of "premises wiring", the premises wiring ends at the outlet, which would be the receptacle on the generator. So it seems to me the cord and plug are part of the "utilization equipment", not the "premises wiring". If this is correct, then 250.20 doesn't require a stand-alone generator serving only cord-and-plug connected loads to be grounded.

Also, more broadly, I would think that a general principle of NEC interpretation is that if two sections are in conflict, the more specific section takes precedence. Is this correct? If so, I would think that 250.34 trumps 250.20.

Just my two cents.

Cheers, Wayne

 

[iwire]

I declare either I am blind or have no reading comprehension at all

My vote is limited comprehension......:grin: (JK)


Have a greatChristmas Mike.

 

[crossman]

Also, more broadly, I would think that a general principle of NEC interpretation is that if two sections are in conflict, the more specific section takes precedence. Is this correct? If so, I would think that 250.34 trumps 250.20.

I am thinking along the same lines.

Since 1999 there has been a trend of doing away with "exceptions" and replacing them with "positive" text. So, there are "general rules" in the code which are subsequently over-ridden by special circumstances in later sections. There are several places where this occurs in the NEC.

For instance:

250.20 gives the rules for determining when a system shall be grounded.

250.21 gives some rules for when systems are not required to be grounded.

In the context of Article 250, Section 250.20 is a very "in general" rule as inteneded by the CMP. I say this because 250.21 immediately allows us to violate 250.20 under certain conditions.

For example: single phase 120 volt control transformer.

250.20(B)(1) will require this system to be grounded which in the 2008 code means connected to earth.

But, 250.21(3) negates that, by saying that the above transformer is not required to be grounded under specific circumstances.

My point is that 250.20 says the system in our example must be grounded but 250.21 turns around and says that there are times when this system is not required to be grounded.

Obviously the intent of the CMP is that 250.20 is to be applied generally and other sections may over-ride it.

With that in mind, turn to 250.34. This gives some more "special case" rules which essentially over-ride 250.20.

But, I admit the new definition of "ground" does cause some confusion with generators as Don is pointing out. And the whole thing makes me want to read Holt's literature of "grounding versus bonding" because I see alot of conflict with the terminology.

 

[jwelectric]

My vote is limited comprehension......:grin: (JK)

The wife read this and she agrees with you :grin:

The wife told me to also say that it is true that I am blind in my right eye and that means that I am half blind or it takes me twice as long to see something that is right in front of me.

Have a greatChristmas Mike.

Hope you and your family has a great and wonderful christmas also.

Edited to add the text that is in red

 

[nakulak]

would it be possible for someone to concisely condense the consensus on this subject (do most agree that a generator now has to have an electrode or is it the reverse ?) (I tried to follow this thread but its giving me a headache)

 

[don_resqcapt19]

Mike,
If we supply a 120 volt single phase circuit, that circuit is required to be supplied by a grounded system.

(B) Alternating-Current Systems of 50 Volts to 1000 Volts Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions:
(1) Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts

The rule in 250.34 does not say that the system supplied by the portable generator is not required to be a grounded system. It only says that you are not required to connect the generator frame to a grounding electrode. Under the 2005 code there was no problem with supplying a grounded system from a portable generator as the neutral was bonded to the frame and the frame was "some other conductive body that serves in place of the earth". At that point in time there was no conflict between 250.20 and 250.34. Now comes the 2008 code and the only way we can have a grounded system is to have a connection to earth and the only way to do that is to have a grounding electrode. That places 250.20 and 250.34 in conflict under the 2008 code.
It is my opinion that the best way to fix this would be to have an exception that says systems supplied by cord and plug connections from a portable or vehicle mounded generator are not required to be grounded systems.
Don

 

[tryinghard]

would it be possible for someone to concisely condense the consensus on this subject (do most agree that a generator now has to have an electrode or is it the reverse ?) (I tried to follow this thread but its giving me a headache)

From Mike Holts Grounding verses Bonding, 5th Edition, pg 45, 250-34 "Generators-Portable and Vehicle-Mounted":

NEC 2008, 250-34(A) "The frame of a portable generator shall not be required to be connected to a grounding electrode"

It's obvious, for all the 2.5-5kva...portable generators: the electricians who disagree with 250-34 should create a ufer (because it's the best), and the electricians who do agree with 250-34 will continue as it states. :-? :grin:

 

[nakulak]

thx .

 

[suemarkp]

The rule in 250.34 does not say that the system supplied by the portable generator is not required to be a grounded system. It only says that you are not required to connect the generator frame to a grounding electrode. Under the 2005 code there was no problem with supplying a grounded system from a portable generator as the neutral was bonded to the frame and the frame was "some other conductive body that serves in place of the earth". At that point in time there was no conflict between 250.20 and 250.34. Now comes the 2008 code and the only way we can have a grounded system is to have a connection to earth and the only way to do that is to have a grounding electrode. That places 250.20 and 250.34 in conflict under the 2008 code.

I think I see what you're trying to say, and it goes back to the definition of premisis wiring. Reading the definition, it sounds like just about all wiring is covered by this (interior, exterior, except for wiring internal to some things). I've always associated premises with a building, but there is no mention of building in the definition.

Are you saying a generator is a premises wiring system, or an extension cord is a premises wiring system? I think the generator is exempted because of the "wiring internal to appliances, ..." caveat. The problem is the extension cord. To me, this is where it should be fixed. If premises wiring system includes a lone extension cord that is laying in the grass (temporary exterior wiring), that definition is too broad.

If you power a building from a receptacle on a generator, it will be grounded because the building is grounded. But portable tools, whether powered via and extension cord or not, shouldn't have to have a grounded source.

 

[tryinghard]

Mike,
If we supply a 120 volt single phase circuit, that circuit is required to be supplied by a grounded system.

(B) Alternating-Current Systems of 50 Volts to 1000 Volts Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions:
(1) Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts

The rule in 250.34 does not say that the system supplied by the portable generator is not required to be a grounded system. It only says that you are not required to connect the generator frame to a grounding electrode. Under the 2005 code there was no problem with supplying a grounded system from a portable generator as the neutral was bonded to the frame and the frame was "some other conductive body that serves in place of the earth". At that point in time there was no conflict between 250.20 and 250.34. Now comes the 2008 code and the only way we can have a grounded system is to have a connection to earth and the only way to do that is to have a grounding electrode. That places 250.20 and 250.34 in conflict under the 2008 code.
It is my opinion that the best way to fix this would be to have an exception that says systems supplied by cord and plug connections from a portable or vehicle mounded generator are not required to be grounded systems.
Don

Okay I think I got it, so 250-34 is a grounded system without a ground connection, and the definition of grounded in '08' is:

Grounded (Grounding). Connected (connecting) to ground or to a conductive body that extends the ground connection

, and ground

The earth

, but the generators frame is in '05' that is absent in '08'

some other conductive body that serves in place of the earth

, that can serve as the

grounding electrode system supplied by the generator

. Meaning it cannot be the conductive body that extends the ground connection because there is no real ground, all the while the generator is considered a grounded system due to 250-20(B)(1)

Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts

, it is not considered an ungrounded system because of its bond to frame yet not truly grounded with a physical connection to earth.

I'm good to go now, ugh :roll: :-? :-?

Honestly Don, I think you've explained the ambiguity well and I agree with your wording to fix it.

 

[cschmid]

I need to bump this just so I can read it in its entirety