Generator Neutrals

Status
Not open for further replies.
Re: Generator Neutrals

Further as far as safety of multiple grounded neutrals, Section 250-184 (b) 1999 NEC or 250.184 (D) 2002 NEC allows for Multiple Neutral bonds in systems over 1 KV indicating there is not an electrical risk in the multiple bonding... It would seem to me that the multiple bonded neutrals in a portable gen back up situation is not only not a violation of the NEC but perfectly safe electrically!
-Derek
 
Re: Generator Neutrals

It would seem to me that the multiple bonded neutrals in a portable gen back up situation is - - - - perfectly safe electrically!
-Derek
Click to expand...
Do you think it's OK to have unbalanced load current flowing through equipment bonding conductors?

Ed

Gen8.gif
 
Re: Generator Neutrals

[/QUOTE]Do you think it's OK to have unbalanced load current flowing through equipment bonding conductors?

Ed

QUOTE]

You do in the situation I described for over 1 KV and the code class I am in showed a picture exactly like what we are talking about. I realize that it does not pertain to the voltage we are discussing but what is the difference electrically? Safe or not safe is the question... And if the Generator disconnect for source to the circuits is a two pole breaker in the main electrical panel that would appear to be the service disconnecting means for that seperately derived service... I am not convinced and I belive tha t is why US manufacturers can sell two pole gen transfer panels with bonded neutral generators...
 
Re: Generator Neutrals

Further Ed, look at your drawing... the unbalanced load will seek the shortest path back to the source... through the neutral to the generator. NOT through the neutral to the main panel to the ground bar to the transfer switch ground to the generator... Yes they are all connected but you are not considering what is the the shortest path.
 
Re: Generator Neutrals

Originally posted by ddderek:
Further Ed, look at your drawing... the unbalanced load will seek the shortest path back to the source... through the neutral to the generator. NOT through the neutral to the main panel to the ground bar to the transfer switch ground to the generator... Yes they are all connected but you are not considering what is the the shortest path.
Click to expand...
ddderek which path is 'shorter' has very little to do with it. Electricity takes all paths not just the shortest path.

Consider a barrel of water with two holes in the bottom. One hole is 1" in diameter and the other hole is 6" in diameter.

The 6" hole has less resistance to flow than the 1" hole and more water will leak out the 6" hole.

But at the same time water will still be flowing out of the 1" hole the entire time.

I have no idea about systems over 600 volts and I was not at your class to see for myself what was taught, but it is an NEC violation to connect the neutral to ground more than once on the same system.

These two sections pretty much spell it out.

1 tells us where we have to bond it and 5 tells us where we can't bond it.

250.24 Grounding Service-Supplied Alternating-Current Systems.

(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).

(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.

(5) Load-Side Grounding Connections. A grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article.
Click to expand...
 
Re: Generator Neutrals

Derek,
If you look at the position of the transfer switch in my diagram you will note that the load is on utility power as shown. The source is the transformer.

the unbalanced load will seek the shortest path back to the source
Click to expand...
Not correct. As Bob stated, the unbalanced load current will follow all available paths back to the source, and the division of the current is inversely proportional to the resistance of each path.

Ed

[ February 13, 2005, 10:12 PM: Message edited by: Ed MacLaren ]
 
Re: Generator Neutrals

The paths are electrically paralleled. While the unbalanced current may not divide evenly, some of it will definitely flow through the bonding conductors.

The "shortest" path (least impedance) is only the path that most will take. Looking at illustration, you have no idea which path has the lowest impedance.
 
Re: Generator Neutrals

OK, I concede your interpretation of the code without conceding the level of danger associated with that type of install.

Next situation:
200A service disconnect outside of house feeding panel inside 50 ft. away,

Neutral bonded at Service disconnect outside,

Transfer switch at panel location,
Generator with floating neutral, outside of house feeding transfer switch...

Approved or violation?

Neutral bond is only at service, but path from gen power is through transfer switch and main panel to service disconnect then back... long way around and not at source while on gen power...
 
Re: Generator Neutrals

Originally posted by ddderek:
OK, I concede your interpretation of the code
Click to expand...
I would be very interested to here another interpretation of those sections I posted.

As far as the 'level of danger' we could talk about it but that will not change what the code requires.

I was thinking about the high voltage systems you spoke of and it strikes me that the utility does not run separate grounded and grounding conductors. So the multiple bonds you saw were only to earth, no conductor is in parallel with the combination neutral and ground of the POCOs.
 
Re: Generator Neutrals

Originally posted by ddderek:
Further as far as safety of multiple grounded neutrals, Section 250-184 (b) 1999 NEC or 250.184 (D) 2002 NEC allows for Multiple Neutral bonds in systems over 1 KV indicating there is not an electrical risk in the multiple bonding...
Click to expand...
Derek looking at 250.184(D) I see that is talking about Multigrounded Neutral Conductors, that is the same system the power company uses and there is not a separate grounding conductor with that system.

Without the separate grounding conductor a parallel path is not created by multiple bonds.

You are trying to compare apples to oranges, multiground neutral systems are entirely different than a premise wiring system.
 
Re: Generator Neutrals

Actually the picture that was showed in the code upgrade class by the inspector was not referring to the typical utility situation. It showed a ground and ground rod at each location as well as the neutral bond at each. The picture CLEARLY showed multiple paths highlighted. My partner sitting next to me said there you go, because we had been discussing this as well. I reminded him that the picture referred to over 1 KV but yes the situation was exactly the same...

As for the different interpretation, as I said, I think one could argue that with the gen transfer switch located in the main panel, that could also be considered the point of gen service disconnect and a proper place for bonding... but that would be determined by the AHJ of course.

Now how about that next question???
 
Re: Generator Neutrals

Talk about sending inaccurate information or mixed signals. Look at the owners manual link here: http://www.smlindustries.com/manuals/GeneratorOwnersMan.pdf In this manual it shows hook up for a gen transfer panel breaking two conductors. It then goes on to say that all hook ups must be done to NEC or local codes. Further it goes to show that the Generator has a bonded neutral in it's wiring diagram.

So it is inherently telling you to hook it up wrong... but then says follow the NEC...
 
Re: Generator Neutrals

Originally posted by ddderek:
As for the different interpretation, as I said, I think one could argue that with the gen transfer switch located in the main panel, that could also be considered the point of gen service disconnect and a proper place for bonding... but that would be determined by the AHJ of course.
Click to expand...
No not by the AHJ by the NEC. If you want a generator to pick up the entire service than you must use a service rated transfer switch and that switch becomes the service disconnect and the bonding will be done there. Anything on the load side of that service rated transfer switch must have isolated neutrals.

Originally posted by ddderek:
Now how about that next question???
Click to expand...
Ed has some great drawings that I figure he will post that show the two ways of connecting generators.
 
Re: Generator Neutrals

You are trying to compare apples to oranges, multiground neutral systems are entirely different than a premise wiring system. [/QB]
Click to expand...
It appears to be the same as a utility situation but the slide in the class clearly showed and talked about the multiple paths on both the ground and neutral. It was referring to the same situation we are speaking of only higher voltage.
 
Re: Generator Neutrals

An MGN system (Multigrounded Neutral system) does not have a separate grounding conductor. (APPLES)

At a typical house service how many conductor do you get from the utility?

Two ungrounded and one MGN.

The only parallel path is through the earth. (Discounting the possibility of a common metal water supply system.)

A premise wiring system does have a separate grounding conductor. (ORANGES)

Once you bond this MGN at the service panel how many conductors do you now need to run to a dryer?

Two ungrounded, one grounded and one grounding.

Bob
 
Re: Generator Neutrals

QUOTE]If you want a generator to pick up the entire service than you must use a service rated transfer switch and that switch becomes the service disconnect and the bonding will be done there. Anything on the load side of that service rated transfer switch must have isolated neutrals.
Square D makes a generator interlock kit, UL Listed, to interlock the main breaker with a two pole breaker for an alternate source, generator.

If I need a service disconnect outside the house to supply a feeder going through the house to a panel, then I would bond the neutral at that outside disconnect and run 4 wire to the panel. Bonding would be done at the service disconnect outside? But my generator supply would be running to that panel in the house, a 2 pole breaker. OR is it ok to bond the neutral inside at the electric panel even though it is not the first disconnecting means for the service?

Ed has some great drawings that I figure he will post that show the two ways of connecting generators. [/QB]
Click to expand...
I've seen Ed's drawings about the ways to hook up a transfer switch... they are over simplified and don't take this situation into consideration.

Thanks again for all the feedback...

BTW... who or where can I contact someone at the NEC to ask for more regulation and more clear definition of this topic in future codes?
Click to expand...
 
Re: Generator Neutrals

Originally posted by iwire:
An MGN system (Multigrounded Neutral system) does not have a separate grounding conductor. (APPLES)
Bob
Click to expand...
AGAIN... this was NOT referring to the utility supply to a house! The MGN situation in the 2002 NEC Code Analysis class and the picture on the slide, SHOWED a neutral AND a ground going form one point to another and BONDED at BOTH locations... GET IT !!! It showed what we are talking about but was referring to systems over 1 KV.... Now I know the voltage is different but we were talking about the electrical safety of it as well.... geez get a grip man...
 
Re: Generator Neutrals

Originally posted by ddderek:
Originally posted by iwire:
An MGN system (Multigrounded Neutral system) does not have a separate grounding conductor. (APPLES)
Bob
Click to expand...
AGAIN... this was NOT referring to the utility supply to a house! The MGN situation in the 2002 NEC Code Analysis class and the picture on the slide, SHOWED a neutral AND a ground going form one point to another and BONDED at BOTH locations... GET IT !!! It showed what we are talking about but was referring to systems over 1 KV.... Now I know the voltage is different but we were talking about the electrical safety of it as well.... geez get a grip man...
Click to expand...
You said this.

Originally posted by ddderek:
Further as far as safety of multiple grounded neutrals, Section 250-184 (b) 1999 NEC or 250.184 (D) 2002 NEC allows for Multiple Neutral bonds in systems over 1 KV indicating there is not an electrical risk in the multiple bonding...
Click to expand...
Those sections can not be used as support for your argument for multiple bonding of premise wiring systems, GET IT. :D
 
Re: Generator Neutrals

Originally posted by ddderek:
The MGN situation in the 2002 NEC Code Analysis class and the picture on the slide, SHOWED a neutral AND a ground going form one point to another and BONDED at BOTH locations... GET IT !!!
Click to expand...
That would make the whole point of an MGN system pointless as I understand it.

Are you sure that the parallel path this book showed was not simply a parallel path through the earth?

Does anyone have the book in question?

Charlie E. any light you can spread on this?
 
Status
Not open for further replies.
Top