new definition of grounded

[don_resqcapt19]

With code this would be a violation of 250-20(B)(2), you would need to be 480v delta 3w ungrounded for the MCC and you cannot feed a 277v system as ungrounded so one of these needs to pass through a SDS to enable it.

No, there is no requirement to run the grounded or neutral conductor to a panel or equipment that does not need it. There is no violation in running only the 3 phase conductors and an EGC to such equipment. In my example the SDS is a grounded system and feeds both a lighting panel and an MCC. There is no code requirement to run the grounded conductor to the MCC as long as it does not supply any single phase line to neutral loads.

With 250-34(A) "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", it's simply not required.

Like I said much earlier in this thread, it is my opinion that the change in the defintion of grounded makes 250.34(A) void. It is simply not possible to have a grounded system without a grounding electrode because of the change of the definition of grounded.
As far as the defintion of premises wiring I only mentioned that because many say that a portable generator does not supply premises wiring.
Don

 

[tryinghard]

I disagree.
Example:
480/277 3-phase 4-wire* service brought to service equipment. From the service equipment, we have a feeder to a 480 volt 3-phase MCC and another feeder to a Lighting Panel that needs 480/277 3-phase 4-wire. The Lighting Panel feeder needs three phases (hot, ungrounded) and the neutral (grounded conductor) but the MCC only needs three phase (hot, ungrounded) conductors...

Your ungrounded feeder circuit will enable 480v 3ph to function but you are disabling the only reason for an ungrounded system.

Your going to have to think or why an ungrounded system is used (in fact I believe its the only reason for its use), an ungrouded system is used for critical machinary to allow one ground/frame fault without operating the OCPD.

In this view if you feed only phase conductors from a grounded system source you WILL negate its only purpose because now one short WILL operate the OCPD (trip the circuit).
It's not an issue of trying to make the ungrounded system work it is a case to make it right.

 

[jim dungar]

480/277 3-phase 4-wire* ....
* Or whatever the IEEE or whoever's current name for the system is, but who the heck made them god?

Technically, and just to split hairs it is 480Y/277. The 3PH 4W is optional.:smile:

This comes from the American National Standards Institute (ANSI) at least as far back as the early 30's.

 

[jim dungar]

In this view if you feed only phase conductors from a grounded system source you WILL negate its only purpose because now one short WILL operate the OCPD (trip the circuit).
It's not an issue of trying to make the ungrounded system work it is a case to make it right.

I am missing the point you are trying to make. How does using only the ungrounded conductors NEGATE ia grounded system only purpose?

But you are straying from Don's reason for posting. Don is very specifically questioning only the effective re-definition of a grounding electrode conductor and separately dervied system without an "earth" connection.

 

[tryinghard]

No, there is no requirement to run the grounded or neutral conductor to a panel or equipment that does not need it. There is no violation in running only the 3 phase conductors and an EGC to such equipment. In my example the SDS is a grounded system and feeds both a lighting panel and an MCC. There is no code requirement to run the grounded conductor to the MCC as long as it does not supply any single phase line to neutral loads.

Don, I can see we're at an impasse with why 250-20 exists because it does require the grounded conductor on a wye system. I wonder if you would always supply ungrounded system only from a transformer simply because its secondary circuitry does not need a neutral? If so your secondary circuit still allows one short ground fault protection, eliminating the reason for an ungrounded system!

If you feed an ungrounded system from a grounded system you STILL have ground fault protection for 1 short, this is opposite reasoning for an ungrounded system! If you have a 480v motor from your MCC that shorts one phase will it open the breaker?

If you feed an ungrounded system from a grounded system without going through a SDS you will in fact have a grounded system regardless how many conductors you run! Your equipment bonding still originates at the source that is connected to the grounded conductor.

Like I said much earlier in this thread, it is my opinion that the change in the defintion of grounded makes 250.34(A) void. It is simply not possible to have a grounded system without a grounding electrode because of the change of the definition of grounded...

250-34(A) is not ignoring grounding to earth, it IS qualifying that grounding to earth is not necessary with its criteria.

 

[tryinghard]

I am missing the point you are trying to make. How does using only the ungrounded conductors NEGATE ia grounded system only purpose?

But you are straying from Don's reason for posting. Don is very specifically questioning only the effective re-definition of a grounding electrode conductor and separately dervied system without an "earth" connection.

Is the source common to the grounded conductor? If it is there is no way to create a correct ungrounded system because ground fault will go to source XO, an ungrounded system does not have any route to source XO ever.

 

[don_resqcapt19]

trying,

250-34(A) is not ignoring grounding to earth, it IS qualifying that grounding to earth is not necessary with its criteria.

That cannot be done in that section. 250.20 calls for a grounded system.
Either 250.20 has to be changed to say that generator supplied systems are not required to be grounded, or the definition of grounded has to revert back to to the old wording that permits the use of "some conductive object that serves in place of the earth". My whole point in this thread is to say with the new definition there is no way to have a grounded system with out a grounding electrode and that this was an unintended consequence of the change in the definition.

If you feed an ungrounded system from a grounded system without going through a SDS you will in fact have a grounded system regardless how many conductors you run! Your equipment bonding still originates at the source that is connected to the grounded conductor.

I have never said that running the 3 phase conductors and an EGC to a MCC or load results in an ungrounded system. It doesn't. The system will always be a grounded system, however, there is no requirement to run the grounded (neutral) conductor to loads that don't use the grounded conductor. The fact that I have not installed a white wire has nothing to do with the fact that the system is a grounded or ungrounded system.
Don

 

[crossman]

Tryinghard...

First, I respect your opinion. But you are missing the big picture.

There are literally millions of 3-phase motors fed from 3-phase 4-wire Wye systems in the United States. These motors have only 3 ungrounded conductors and an equipment ground. Is there a need to have the grounded conductor at the motor? No. Is it a problem that the system feeding the motor is grounded? NO.

And, we are all totally happy if a single ground fault on one phase shuts the motor down. In most instances, we do not desire the "protection" of an ungrounded system, where a phase can go to ground, but the equipment still runs. In non-critical equipment, this protection from shutting down is not needed. (And probably 80% of motors in the U.S would come under that category.)

There is absolutely nothing wrong with running motors off a wye system. If one desired an ungrounded system, then yes, you would have to either have an ungrounded delta service, or create a new ungrounded delta through transformers. But it is by no means required. And it would certainly be wrong to say that an ungrounded delta is better or safer than a grounded wye for feeding 3 phase motors.

And absolutely there are literally millions of motors running like this right now.

 

[crossman]

Technically, and just to split hairs it is 480Y/277. The 3PH 4W is optional.:smile:

This comes from the American National Standards Institute (ANSI) at least as far back as the early 30's.

Jim, thanks for the reply. I'm just having a little fun. The terminology of our industry has huge variances, from region to region and institution to institution. For example, the Houston City Ordinances have specified color coding for the different systems, but they certainly do not use the ANSI nomenclature in spelling out what systems they are talking about. But yet we all understand what they mean. I will admit that a recognized standard used by all could not hurt.

 

[crossman]

Your ungrounded feeder circuit will enable 480v 3ph to function but you are disabling the only reason for an ungrounded system.

Okay, here is the difference in our thinking as others are stating.

You refer to the 3 ungrounded conductors (hots) from the grounded wye as an ungrounded system. That is incorrect. It is still a grounded system and will still have all the benefits of tripping OCP if a phase goes to ground.

Consider if we did run the neutral to the MCC even though it isn't needed. We would terminate the neutral on an isolated neutral bar. There would be nothing else connected to it, and it would be against code to bond it to the metal frame and enclosure. And we would have no other wires attached to that neutral bar... rather pointless.

Now that I think of it, I believe our issues are arising from terminology. In the code, phase conductors are referred to as "ungrounded" conductors even if they are part of a grounded system. So, a 3-wire feeder from a grounded wye will consist of 3 ungrounded conductors. But the system is still grounded even though we are calling the conductors ungrounded.

Edit: further clarification of thought.

Back on topic now.....

 

[tryinghard]

If you have a 480/277v wye grounded system serving a SWB which then feeds 480v 3w circuits to transformers (than include 3ph 4w secondary) and MCC's that in turn feed 3ph 3w circuitry you in fact have a bunch of 3ph 3w circuitry distributing from A GROUNDED SYSTEM and is a grounded system even without the neutral brought with it - all because of its source.

The only way to create an ungrounded system from a grounded system is to route through a transformer. An example would be 480v 3ph 3w primary to 480v 3ph 3w secondary.

 

[tryinghard]

Tryinghard...

First, I respect your opinion. But you are missing the big picture.

There are literally millions of 3-phase motors fed from 3-phase 4-wire Wye systems in the United States....And absolutely there are literally millions of motors running like this right now.

I have no idea what I stated to lead you here?!!?

Maybe you should re-read beginning of this string of post to see who stated, "grounded or ungrounded system" first, it is mislabeling and misuse of terminology that causes article 250 to be convoluted.

 

[crossman]

th, I think I understand the issue of our differences here. We are actually thinking the same thing, it is just a misunderstanding of terms.

When I said that we can take 3 ungrounded conductors from a grounded wye and feed a motor control center, I never said or implied that the system was ungrounded. Again, the NEC uses the term "ungrounded conductors" when referring to hot or phase conductors. Once a wye system is grounded, it is grounded. No doubt about it. And to create a new ungrounded system from the grounded system, you would, as you mention, need a transformer.

Just to make sure we are straight: In grounded systems, the NEC still refers to the phase conductors as "ungrounded conductors" even though the system is grounded.

 

[tryinghard]

trying,

That cannot be done in that section. 250.20 calls for a grounded system.
Either 250.20 has to be changed to say that generator supplied systems are not required to be grounded, or the definition of grounded has to revert back to to the old wording that permits the use of "some conductive object that serves in place of the earth". My whole point in this thread is to say with the new definition there is no way to have a grounded system with out a grounding electrode and that this was an unintended consequence of the change in the definition...

Don,

A little time away and I see this now! I agree with your observance (and appreciate your tenacity - as well as others) the '08' definition does contradict 250-20 and 250-34 doesn't work in this light.
I don't believe a ground rod at every 5KVA portable generator is necessary. I do think the definition could easily be rephrased though.
Sorry for muddling the topic.

 

[tryinghard]

Does the new definition of grounded in the 2008 code cause any issues with the application of 250.34 in the cases where the system supplied by the portable generator is required to be a grounded system by the rules found in 250.20?

Just another shot at clarifying myself
Only if it is a grounded system because 250-20 has no relevance to an ungrounded system like (3ph 3w ungrounded system). 250-20 is only for the grounded systems listed in its body. The requirements of 250-50 for a grounding electrode system (that is grounded) are not to be confused with a grounded system because these are not the same; this is a common place to confuse.

If a particular generator is a grounded system as listed in 250-20 it is affected by its rules and the new definition of ?08? that contradicts 250-20.
But:
If a particular generator is an ungrounded system then 250-20 does not apply and 250-34 allows exemption to an electrode, in other words a portable/trailer generator does not have to have an electrode within the criteria of 250-34. I have some passion here because I?ve hooked up 2 of these in the last 3 months.

 

[don_resqcapt19]

trying,

250-20 is only for the grounded systems listed in its body.

250.20 always applies as it specifies what systems must be grounded, what systems that are not permitted to be grounded and what systems may be grounded. Most of the systems that we commonly use are systems that are required to be grounded systems. If 250.20 requires the system to be grounded or if it permits the system to be grounded and the design requires grounding, then we have a problem with the new definition if the system is supplied by a portable generator.

The requirements of 250-50 for a grounding electrode system (that is grounded) are not to be confused with a grounded system because these are not the same; this is a common place to confuse.

While these rules are not the same they work with each other. Once 250.20 tells you the system must be grounded, then, under the new definition, you must use one of the electrodes specified in 250.50.

If a particular generator is a grounded system as listed in 250-20 it is affected by its rules and the new definition of ‘08’ that contradicts 250-20.

There is no conflict between 250.20 and the definition, the conflict is between the definition and 250.34.
Don

 

[jwelectric]

I am not sure that I understand either point so, please let me ask a couple of questions as I am eager to learn as much as I possibility can about connecting to earth (grounding).

250.20(B) addresses AC systems of 50 to 1000 volts and requires that the system be ?grounded? (connected to earth)
250.20(D) addresses separately derived systems and refers to 250.30.

250.34(A) addresses portable generators as they were being used as a stand alone system and not connected to any building
250.34(C) addresses a generator that is being used as a separately derived system.

If connecting the generator to a building as outlined in 700, 701 and 702 and the bonding to the neutral point is not bonded at the generator it will be connect to earth at the building.
If the bonding to the neutral point is taking place at the generator then the grounded conductor can not be connected to the grounding electrode system at the building and a grounding electrode system is now required at the generator or the separately derived system.

Where is the confusion of 250.20 and 250.34 being brought up with the new definition?
The generator is going to be connected to earth at one point or the other or it is not going to be connected to anything except a cord in which case 250.34 relieves the installation of a grounding electrode system. Notice that there is no mention of an equipment grounding conductor in 240.34 only the mention of the terminal which is allowed to connect to the frame.

Am I totally lost????

 

[don_resqcapt19]

Mike,

The generator is going to be connected to earth at one point or the other or it is not going to be connected to anything except a cord in which case 250.34 relieves the installation of a grounding electrode system.

Under the 2005 code I would have agreed with that, but not with the new defintion. 250.20 requires that a 120/240 volt system be a grounded system. With the new definition, the only way to get a grounded system is to make a connection to earth. It is my opinion that the new defintion of grounded is in conflict with 250.34 any time you are required to have a grounded system that is supplied by a portable generator.
Don

 

[76nemo]

Lost

Lost

Lost, I am. From what little I know as far as code, isn't the main to be the only one to accept the ground fault? Please excuse my NEC ignorance, I am not a construction guy.

 

[tryinghard]

Don,

250.20 always applies as it specifies what systems must be grounded, what systems that are not permitted to be grounded and what systems may be grounded.

If you are saying 250-20 applies to ungrounded systems, specifically where does it address ungrounded systems?

If 250.20 requires the system to be grounded or if it permits the system to be grounded and the design requires grounding, then we have a problem with the new definition if the system is supplied by a portable generator.

But you say in the end of your post #36 ?There is no conflict between 250-20 and the definition?, what do you mean above?

Once 250.20 tells you the system must be grounded, then, under the new definition, you must use one of the electrodes specified in 250.50.

Where does 250-20 tell me an ungrounded system must be grounded?

There is no conflict between 250.20 and the definition, the conflict is between the definition and 250.34.

How so?