stand-alone generators

[jwelectric]

Please explain.

Being that we are discussing these small generators let?s keep the discussion on residential systems for simplicity.

From the secondary of the utility company?s transformer to the home are two hot and one center tap neutral conductors. The current supplied by this system will travel from the transformer back to the transformer on these three conductors.

The center tap of this system is connected to earth for the reasons outlined in 250.4(A)(1).

Other electrical systems delivered to a home such as telephone and cable are also required to be connected to earth and must use the same system to connect to earth as the electrical system uses.

This earth connection of the multiple systems does not constitute a parallel path for any one of the systems unless there is something abnormal happening in which case the resistance of the smaller conductors would limit the amount of current imposed on the lower voltage systems.

With the generator where the neutral is bonded at both places the supplying cord will have two equal sized conductors in parallel which will just about divide the current in half on each one. This will elevate the potential of the frame of the generator above the potential of earth and allow current to pass through the person in contact with the generator frame based on the amount of resistance of earth.

In a code compliant properly installed system the amount of current flow between the grounding electrode systems between two homes would be infinitesimal to say the least. With the generator it could be as much as half the current or more and could be deadly.

To float the neutral in the generator and a fault to the frame occur while the person is connecting this death trap and come in contact with the other leg and the frame then they are between a 240 volt potential.

Now back to the original question, why does the UL White Book in FTCN make the statements that a generator with the supply being taken from the generator from a receptacle must be installed as a SDS?

 

[Dennis Alwon]

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I thought that the NEC was the NFPA! :blink:

* * *

The NFPA publishes the NEC but it has no control over UL or the manufacturer. At least that is what I think was being said. I disagree somewhat in the sense that if a code change affects a product they will change it. Now who is asking for the change may be a different issue. TR recep. were required so the manufacturers came out with them but was it the manufacturers that pushed it thru???? Either way there seems to be a cause and effect.

 

[iwire]

From the secondary of the utility company?s transformer to the home are two hot and one center tap neutral conductors. The current supplied by this system will travel from the transformer back to the transformer on these three conductors.

The center tap of this system is connected to earth for the reasons outlined in 250.4(A)(1).

Other electrical systems delivered to a home such as telephone and cable are also required to be connected to earth and must use the same system to connect to earth as the electrical system uses.

This earth connection of the multiple systems does not constitute a parallel path for any one of the systems unless there is something abnormal happening in which case the resistance of the smaller conductors would limit the amount of current imposed on the lower voltage systems.

Mike, this statement is false

This earth connection of the multiple systems does not constitute a parallel path for any one of the systems unless there is something abnormal happening

The parallel path is there regardless of an abnormal condition.

 

[iwire]

The NFPA publishes the NEC but it has no control over UL or the manufacturer. At least that is what I think was being said.

Exactly what I was trying to say.

I disagree somewhat in the sense that if a code change affects a product they will change it.

I agree if the code changes so that a product can no longer be installed the manufacturers will often change the product so they can keep selling it.

However that is their choice to do so, the NFPA cannot force it.

But we were talking about UL and there is nothing the NEC / NFPA can do to force UL to do anything.

 

[Dennis Alwon]

I agree if the code changes so that a product can no longer be installed the manufacturers will often change the product so they can keep selling it.

However that is their choice to do so, the NFPA cannot force it.

But we were talking about UL and there is nothing the NEC / NFPA can do to force UL to do anything.

Is it really a choice? If you don't produce the product then you won't be in business long. Not much of a choice

 

[iwire]

Is it really a choice? If you don't produce the product then you won't be in business long. Not much of a choice

:slaphead:

Say you are Hubble, you make a lot of products, the loss of one product is not going to put you out of business.

So Hubble could have decided the profits would not be high enough to make a residential grade TR duplex, or they could decide it is.

Bottom line is it is a choice, the NFPA cannot call a manufacturer and say 'You will do X, Y and Z'.

 

[suemarkp]

The parallel paths are not just an earth path. With CATV, the metal shield goes back to the wire on the pole which has a metal shield which goes to your neighbor who has also bonded it to their neutral. Even if the neighbor has a different transformer, his neutral will be connected to your source grounded conductor. So there is a complete parallel WIRE path between your house and your service transformer neutral.

Same with metal water pipes if the buried pipe in the street is metal. Phones may also be this way, but not sure if there are shields on all cabling. Probably from each house to the street box, so at least some houses are all tied together through phone shields.

 

[iwire]

The parallel paths are not just an earth path.

I agree, and I am sure Mike knows that.

With CATV, the metal shield goes back to the wire on the pole which has a metal shield which goes to your neighbor who has also bonded it to their neutral. Even if the neighbor has a different transformer, his neutral will be connected to your source grounded conductor. So there is a complete parallel WIRE path between your house and your service transformer neutral.

And it is there 24/7 365 in a code compliant and correct installation.

 

[don_resqcapt19]

Being that we are discussing these small generators let?s keep the discussion on residential systems for simplicity.

From the secondary of the utility company?s transformer to the home are two hot and one center tap neutral conductors. The current supplied by this system will travel from the transformer back to the transformer on these three conductors.

The center tap of this system is connected to earth for the reasons outlined in 250.4(A)(1).

Other electrical systems delivered to a home such as telephone and cable are also required to be connected to earth and must use the same system to connect to earth as the electrical system uses.

This earth connection of the multiple systems does not constitute a parallel path for any one of the systems unless there is something abnormal happening in which case the resistance of the smaller conductors would limit the amount of current imposed on the lower voltage systems.

It is much more than a parallel path via the earth. It is an actual physical path via the bonding connections at each building, the main bonding jumpers at each building and the telephone or cable shield. Yes it is a high resistance path, but it is the total parallel resistance of all of the path that determines the voltage drop. As long as the service grounded conductor is in good condition, the voltage drop will be minimal and there is no real hazard.

With the generator where the neutral is bonded at both places the supplying cord will have two equal sized conductors in parallel which will just about divide the current in half on each one. This will elevate the potential of the frame of the generator above the potential of earth and allow current to pass through the person in contact with the generator frame based on the amount of resistance of earth.

The only voltage that would be on the frame when the grounded conductor and EGC are connected in parallel would be the voltage drop on those conductors. Assuming that they are correctly sized for the load this voltage drop would not be a hazard. It would be a couple of volts at most.

We have the same thing with every service. The service equipment is not really at ground or earth potential. If you would measure from anything connected to the electrical grounding system to remote earth (remote earth being defined as earth outside the influence of any grounding electrode, often stated as 50' from any other electrode) you will measure voltage. This voltage is the voltage drop on the utility primary neutral and the service grounded conductor.

In a code compliant properly installed system the amount of current flow between the grounding electrode systems between two homes would be infinitesimal to say the least.

The amount of current on the grounding electrode systems is dependent on the electrodes used. If you have a common metal underground water piping system, it is not uncommon to find 20% or more of the grounded conductor current flowing on the parallel path via the water piping.

With the generator it could be as much as half the current or more and could be deadly.

I am just not seeing how this results in a deadly amount of voltage. The only voltage that would be on the frame is equal to the voltage drop on the conductors.

To float the neutral in the generator and a fault to the frame occur while the person is connecting this death trap and come in contact with the other leg and the frame then they are between a 240 volt potential.

Assuming a cord and plug connection via a generator mounted GFCI, the GFCI would trip in this case.

Now back to the original question, why does the UL White Book in FTCN make the statements that a generator with the supply being taken from the generator from a receptacle must be installed as a SDS?

That would be to make the system code compliant when a generator that is listed to UL 2201. That being said, I have not found and evidence that there are any products so listed. The UL Guide Information does not apply in general. It only applies to products listed to the standard that the Guide Information references. To say it applies to all generators is like saying a Chevy service manual applies to all motor vehicles.

 

[jwelectric]

In your post above you mention two different aspects if an electrical system. When you addressed the parallel path for the generator you discussed the voltage being dropped across the conductors but when you discussed the metal water pipe you mentioned the amount of current on them.

What about the current on the frame of the generator and the voltages on metal water pipes?

 

[don_resqcapt19]

In your post above you mention two different aspects if an electrical system. When you addressed the parallel path for the generator you discussed the voltage being dropped across the conductors but when you discussed the metal water pipe you mentioned the amount of current on them.

It is the voltage drop on all of the parallel paths that drives the current through each of the paths. The current divides in inverse proportion to the impedance of each path.

What about the current on the frame of the generator and the voltages on metal water pipes?

The only voltage on either the generator frame or the water pipe is the voltage drop across all of the parallel paths. As long the the circuit grounded conductor is without problems, this voltage drop will be small.

The current split between the EGC and the grounded conductor on the circuit between the generator and the building would be approximately 50/50 based on your previous statement that these two conductors are of the same size. I would expect little to no current on the metal frame of the generator unless the generator manufacturer used the frame as the EGC to generator mounted receptacle. I have only taken a couple of small generators apart, and the frame was bonded, but there was a wire from the frame bonding point to the ground terminal on the receptacle. If the frame was used as the EGC, and assuming that the impedance of the current path through the frame to the winding is equal to or less than the impedacne of the circuit EGC, about 50% of the current would be on the frame.

 

[jwelectric]

It is the voltage drop on all of the parallel paths that drives the current through each of the paths. The current divides in inverse proportion to the impedance of each path.

Both being equal the voltage would be half, correct?

The current split between the EGC and the grounded conductor on the circuit between the generator and the building would be approximately 50/50 based on your previous statement that these two conductors are of the same size. I would expect little to no current on the metal frame of the generator unless the generator manufacturer used the frame as the EGC to generator mounted receptacle. I have only taken a couple of small generators apart, and the frame was bonded, but there was a wire from the frame bonding point to the ground terminal on the receptacle. If the frame was used as the EGC, and assuming that the impedance of the current path through the frame to the winding is equal to or less than the impedacne of the circuit EGC, about 50% of the current would be on the frame.

Okay we have established that there could be as much as 15 amps of current on the frame of a portable stand-alone generator that is supplying a system from a 30 amp receptacle mounted on the frame of the generator.

What would be the outcome should someone make the third parallel path from the grounding electrode system of the wiring system being served and the frame of the generator?

To add one more stir to the pot what could the outcome be should the neutral connection be lost through the plug-in connections?

 

[ActionDave]

Both being equal the voltage would be half, correct?




Okay we have established that there could be as much as 15 amps of current on the frame of a portable stand-alone generator that is supplying a system from a 30 amp receptacle mounted on the frame of the generator.

What would be the outcome should someone make the third parallel path from the grounding electrode system of the wiring system being served and the frame of the generator?

Why would this be any different than the existing, required, parallel paths?

 

[don_resqcapt19]

Both being equal the voltage would be half, correct?

No, it is a parallel circuit, the voltage drop is the same on all paths. In the example of the cord and plug connected load with a full size EGC in the cord and the EGC in parallel with the grounded conductor, the votlage drop would be 1/2 of what it would be in a code compliant installation.

Okay we have established that there could be as much as 15 amps of current on the frame of a portable stand-alone generator that is supplying a system from a 30 amp receptacle mounted on the frame of the generator.
What would be the outcome should someone make the third parallel path from the grounding electrode system of the wiring system being served and the frame of the generator?

You would have one more current carrying path and the voltage drop would be less.

To add one more stir to the pot what could the outcome be should the neutral connection be lost through the plug-in connections?

In the example that we are talking about, we would have a single path for the grounded conductor current and the voltage drop would be the same as with a code compliant installation.

 

[jwelectric]

In a parallel path the applied voltages is the same in all nodes and the current will divide according to the amount of resistance.

Therefore the voltage potential on the frame of a dual bonded generator will be within a fraction of a volt as the conductor of a properly installed generator. Is this not correct?

 

[jwelectric]

Why would this be any different than the existing, required, parallel paths?

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

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.

What is being discussed here is the intentional connection of two conductors in one system. The comparison of the two is like comparing the New Moon to the Sun.

 

[iwire]

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.

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.

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.

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.

 

[don_resqcapt19]

...Therefore the voltage potential on the frame of a dual bonded generator will be within a fraction of a volt as the conductor of a properly installed generator. Is this not correct?

It could very well be a couple of volts. It would depend on the load and the wire size.

 

[don_resqcapt19]

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

There is no parallel path via the EGC in a code compliant installation. However on the line side of the service there are multiple parallel paths in a code compliant installation.

What is trying to be construed as being parallel paths is the connection of different systems to earth.

I have never been talking about parallel paths via the earth and multiple electrodes. I have only been talking about acutal physical metallic parallel paths, like a common metal underground water pipe or the shield of the TV cable system. These are physical paths because they are continuous and are bonded to the electrical systems in multiple buildings.

The only way this poses a danger is if something goes wrong with one system or the other. ...

And that is the only way the multiple bonding of the generator circuit poses a danger...when there is at least two failures. A single failure does not pose a danger.

 

[jwelectric]

And that is the only way the multiple bonding of the generator circuit poses a danger...when there is at least two failures. A single failure does not pose a danger.

I don?t understand your reasoning here. If the neutral and grounding conductor is bonded on both ends and are the same size then they both will be carrying the same amount of current and be at the same voltage level. The metal frame of the generator will be carrying current at the same voltage level therefore a danger.

The metal water pipe and the shielding of cable will not be carrying enough current to hurt someone unless there is something wrong. The NEC does not address installations that have something wrong but does address compliant installations.

This comparison in my opinion is useless for a defense of having a non-compliant installation. Using the above mention of metal water pipes and so forth as a defense to making a non-compliant installation for generators why not just use the neutral for bonding between panels? Or better still just bond the EGC to the neutral in all panels and every other place they are in the same enclosure?