stand-alone generators

[jwelectric]

There is no existing parallel path where the neutral and equipment grounding conductors are intentionally bonded on both ends.

Mike, that is a falsehood and I have no idea why you persist in stating it.

I have made a true and exact statement that can be confirmed with an ammeter. To explain would be outside the scope of this forum but I think you already understand.

What is trying to be construed as being parallel paths is the connection of different systems to earth. The only way this poses a danger is if something goes wrong with one system or the other.

No Mike, it is not just a connection via dirt, it is connection via aluminum or copper conductors. And this parallel path exists in a correctly installed and operating system.

And this connection will have little or no current unless something goes wrong which would lead into the discussion of a non-compliant installation.

What is being discussed here is the intentional connection of two conductors in one system.

Which is exactly the case when a coax shield is tired into the AC system.

Unless you are saying that the electrical utility and the cable is the same system then I would tend to believe that they are two separate systems.

The comparison of the two is like comparing the New Moon to the Sun

I disagree and you have yet to show why it is different other than you would like it to be.

See the many post concerning the bonding of the EGC and the neutral from the generator to the premises wiring system that shows that the same amount of current will be present on both conductors at the same time. Now with the deepest of respect I ask you to show me where the same amount of current will be present on the shielding of the cable service as on the neutral of the utility service. This is why my comparison to the moon and the sun, both shed light but one is much brighter than the other.

 

[don_resqcapt19]

I have made a true and exact statement that can be confirmed with an ammeter. To explain would be outside the scope of this forum but I think you already understand.


And this connection will have little or no current unless something goes wrong which would lead into the discussion of a non-compliant installation.

It is a physical parallel path and the current will divide in inverse proportion to the impedence of the paths.

Unless you are saying that the electrical utility and the cable is the same system then I would tend to believe that they are two separate systems.

The cable shield is required to be physcally bonded to the grounding system at each building served. The grounding system is bonded to the grounded conductor at each building served. This creates multiple physical parallel paths for the grounded conductor current.

See the many post concerning the bonding of the EGC and the neutral from the generator to the premises wiring system that shows that the same amount of current will be present on both conductors at the same time.

The same amount of current is on those two paths only because you said that the grounded conductor and the EGC were of the same size and therefore they would have almost equal impedences resulting in near equal current.

Now with the deepest of respect I ask you to show me where the same amount of current will be present on the shielding of the cable service as on the neutral of the utility service.

No one has ever said that the current on the cable shield would be equal to that of the grounded conductor. Again the amount of current is based on the impedance of the paths. The impedence of the cable shield is much higher and results in much less current flow. Remember that it is not just the resistance of the paths but the impedence because we are dealing with AC current. Physical separation between the supply and return paths causes an increase in the impedence of the remote path.

This is why my comparison to the moon and the sun, both shed light but one is much brighter than the other.

Under normal conditions there is, as you say, much less current on the cable shield, however under abnormal conditions such as an open neutral, the cable shield may try to carry the full grounded conductor current. I was involved in the investigation of two fires that resulted from the high current on the cable shield when the service neutral was lost.

 

[jwelectric]

Under normal conditions there is, as you say, much less current on the cable shield, however under abnormal conditions such as an open neutral, the cable shield may try to carry the full grounded conductor current. I was involved in the investigation of two fires that resulted from the high current on the cable shield when the service neutral was lost.

But there does not have to be anything abnormal for current to be present on the EGC of a generator that has a bond at both the generator and the transfer switch which could lead to the same innfestiation without something abnormal would you agree?

 

[ActionDave]

I am not the cantankerous sort at all and I am not trying to be, but I am not seeing the safety issue. A code and/or listing issue, yes.

If a temp generator is powering a building and I lean on while drinking a cup of coffee on my break; how am I in danger of getting a shock if the neutral is bonded at generator and not switched at the building?

 

[don_resqcapt19]

But there does not have to be anything abnormal for current to be present on the EGC of a generator that has a bond at both the generator and the transfer switch which could lead to the same innfestiation without something abnormal would you agree?

There is nothing abnormal with the current on the service conduit, metal underground water pipe or the cable shield either. There will be current on the EGC that is connected in parallel with the neutral like we have been talking about in this thread. As has been said many times, this is a code violation. I still don't see a safety issue with the neutral and EGC in parallel between the generator and the building. Can you tell me exactly what hazard there is? I am just not seeing one.

If you install a generator without a neutral bond at the generator, there will be more votlage as measured to "remote earth" then there would be where the generator neutral is bonded to the frame and the neutral is not switched by the transfer switch. While this will be a small voltage, it will be twice as much voltage as in the installation we have been talking about in this thread.

 

[T.M.Haja Sahib]

There is nothing abnormal with the current on the service conduit, metal underground water pipe or the cable shield either.

Nothing abnormal unless sparking due to it is present,which may become a fire hazard.What is your opinion?

 

[jwelectric]

In a normal and compliant installation the amount of current on the shielding of the cable, the grounded conductor of the telephone line, and a metal water pipe would be little to none.

Where the frame of a generator is bonded to the neutral conductor and also the neutral is bonded at the transfer equipment the amount of current will be very high and the voltage for any paralleled circuit is the same as the applied voltage less the voltage drop.

I see it as a very dangerous situation as well as the NEC sees it as something other than safe. UL mandates that a stand-alone generator be installed as a SDS. If the generator carries a UL label it must be installed as a SDS by 110.3(B). If a generator is not listed by UL I would reason what makes it safer than one that is listed and make the installation as though it was listed. The fact that the appliance is not listed will not make it any safer than one that is listed and one that has been listed will in most cases be a lot safer than one that is not.

 

[don_resqcapt19]

In a normal and compliant installation the amount of current on the shielding of the cable, the grounded conductor of the telephone line, and a metal water pipe would be little to none.

That is not true...it is not uncommon to find 25% or more of the grounded conductor current flowing on the water lines where there is a common metal underground water piping system in a code compliant installation.

Where the frame of a generator is bonded to the neutral conductor and also the neutral is bonded at the transfer equipment the amount of current will be very high and the voltage for any paralleled circuit is the same as the applied voltage less the voltage drop.

I have no idea what you are trying to tell me with this statement

I see it as a very dangerous situation ...

Please explain to me the exact danger as I just don't see it.

...as well as the NEC sees it as something other than safe. ...

I understand what the code says and have said that the code requires the generator to be installed with transfer equipment that switches the grounded conductor if the grounded condcutor is bonded to the generator frame.

UL mandates that a stand-alone generator be installed as a SDS.

UL's rules only apply to equipment listed to their standards. They do not apply in general.

If the generator carries a UL label it must be installed as a SDS by 110.3(B).

Have you found any listed portable generators? I don't find any shown on the UL database when I do a search.

If a generator is not listed by UL I would reason what makes it safer than one that is listed and make the installation as though it was listed. The fact that the appliance is not listed will not make it any safer than one that is listed and one that has been listed will in most cases be a lot safer than one that is not.

A listed product may or may not be safer than an unlisted one.

 

[jwelectric]

In a normal and compliant installation the amount of current on the shielding of the cable, the grounded conductor of the telephone line, and a metal water pipe would be little to none.

That is not true...it is not uncommon to find 25% or more of the grounded conductor current flowing on the water lines where there is a common metal underground water piping system in a code compliant installation.

And somewhere in that system you will find something abnormal with a neutral. If there was not something wrong with a neutral somewhere there would be a lot less than 25% current on the metal water pipe although I do remember the shielding of coax being added to this discussion at some point in time as well as the grounded conductor of a telephone system.

Where the frame of a generator is bonded to the neutral conductor and also the neutral is bonded at the transfer equipment the amount of current will be very high and the voltage for any paralleled circuit is the same as the applied voltage less the voltage drop.

I have no idea what you are trying to tell me with this statement. Please explain to me the exact danger as I just don't see it.

The amperage on the frame of the generator will be in parallel with the neutral of the system. Should someone make contact with the frame while standing on the ground they now become the third node of this parallel path. The amount of current flowing through this person will be solely dependent on the amount of resistance between where they are touching the frame and the grounding electrode system of the premises system being served. The amount of resistance will depend on such things as the weather conditions, the type and condition of foot ware if any, the type of grounding electrode system, ect??..

If there was no danger then the NEC would not mandate the differences between a SDS and a non-SDS. Remember that the NEC is a minimum safety standard and to do anything less will constitute an unsafe installation.

 

[T.M.Haja Sahib]

In a normal and compliant installation the amount of current on the shielding of the cable, the grounded conductor of the telephone line, and a metal water pipe would be little to none.

But when a heavy ground fault occurs,sparking could occur at 'poor joints' in above 'conductors' due to extraneous current flow in them.This may be a fire hazard.

 

[don_resqcapt19]

And somewhere in that system you will find something abnormal with a neutral. If there was not something wrong with a neutral somewhere there would be a lot less than 25% current on the metal water pipe although I do remember the shielding of coax being added to this discussion at some point in time as well as the grounded conductor of a telephone system.

No that is with a perfect neutral. Remember that we are often talking about copper pipe that has a metallic connection to a cast iron main. The resistance of this path may very well be less than that of the grounded conductor. It is the fact that it is a remote path that increases the impedence and reduces the current on the water pipe system. Also, this is not common in newer areas as the bell and spigott connection with a rubber gasket on the cast iron mains breaks the path.
As far as the telephone and cable paths, they are of much higher impedence and have little current on them. In the case of the metal underground water piping system, you can lose the service neutral and not even know it as the pipe will provide the path for the neutral current.
If you lose the neutral and do not have a path via a metal underground water pipe, the current on the TV cable shield and or phone shield may result in a fire. As I have said before, I was involved in two fire investigations were there was not a metal water pipe ground and the service neutral was opened. In both cases the cable bonding wire between the cable shield and the electrical grounding system carried so much current that the bonding wire got hot enough to ignite the wood.

The amperage on the frame of the generator will be in parallel with the neutral of the system. Should someone make contact with the frame while standing on the ground they now become the third node of this parallel path. The amount of current flowing through this person will be solely dependent on the amount of resistance between where they are touching the frame and the grounding electrode system of the premises system being served. The amount of resistance will depend on such things as the weather conditions, the type and condition of foot ware if any, the type of grounding electrode system, ect??..

What voltage is available to drive this current?

If there was no danger then the NEC would not mandate the differences between a SDS and a non-SDS. Remember that the NEC is a minimum safety standard and to do anything less will constitute an unsafe installation.

The NEC is also a fit all document and there is no way it can address every possible condition. I see very little danger in having the grounded and grounding conductors in parallel for a small portable generator.

 

[jwelectric]

Maybe Dennis or Roger can post what Mr. Ode had to say about this type of installation. He went into detail about the task group that was appointed to research this type of installation and explained the dangers.

 

[don_resqcapt19]

Maybe Dennis or Roger can post what Mr. Ode had to say about this type of installation. He went into detail about the task group that was appointed to research this type of installation and explained the dangers.

I would have the same question for him as I had for you. How do the electrons know what side of the service disconnect they are on?

Think about the voltage available to drive current through a person touching the generartor frame and the earth with the parallel path we have been talking about in this thead.

Then think about a code compliant non-SDS installation and the voltage available to drive current through a person touching the frame and the earth.