Portable generator bonding queston

[don_resqcapt19]

If the only bond is on the load side of the GFCI sensors, the current through the GFCI sensors will not show an imbalance in the event of a load side ground fault. There would still be equal current on the two conductors running through the GFCI sensor.

 

[kwired]

If the only bond is on the load side of the GFCI sensors, the current through the GFCI sensors will not show an imbalance in the event of a load side ground fault. There would still be equal current on the two conductors running through the GFCI sensor.

I agree.

 

[T.M.Haja Sahib]

If the neutral to ground bonding is done downstream of the generator GFCI, then the GFCI will not provide any protection.

Yes,you are correct.But if modification is carried out per link in post#5,the subject gen set not only does not comply with OHSA regulation but also its GFCI will not provide any protection against any ground fault inside any building for not separately derived systems.But for separately derived system with four pole transfer switch,it will afford protection against ground faults with its frame grounded.

 

[don_resqcapt19]

Yes,you are correct.But if modification is carried out per link in post#5,the subject gen set not only does not comply with OHSA regulation but also its GFCI will not provide any protection against any ground fault inside any building for not separately derived systems.But for separately derived system with four pole transfer switch,it will afford protection against ground faults with its frame grounded.

A portable generator used to supply a building does not have to comply with the OSHA rules, that is why some generators have a switch to make or break the bonding connection. I doubt that you would ever find a transfer switch that switches the grounded conductor being used with a small portable generator like this thread is talking about.
While having the bond at both the generator and the building is a code violation, I don't see any real hazard or safety issue. It is exactly how a service is connected...bonds at both the utility transformer and the building.

 

[T.M.Haja Sahib]

I doubt that you would ever find a transfer switch that switches the grounded conductor being used with a small portable generator like this thread is talking about.

It depends on the system of grounding adopted.In US,TN system of grounding is adopted.So three pole transfer switches that do not switch neutral are used widely here.But in countries like India or Japan where TT system of grounding is used,three/four pole transfer switches that switch neutral are necessary even for small portable generator like this thread.

While having the bond at both the generator and the building is a code violation, I don't see any real hazard or safety issue. It is exactly how a service is connected...bonds at both the utility transformer and the building.

Utility transformer and its grounding do not come under the purview of NEC.

 

[iwire]

But in countries like India or Japan where TT system of grounding is used,three/four pole transfer switches that switch neutral are necessary even for small portable generator like this thread.

Please stay on topic, we are talking about the US, not India or Japan.

 

[don_resqcapt19]

...
Utility transformer and its grounding do not come under the purview of NEC.

That doesn't have anything to do with my comment. The electrons behave the same way no matter what code governs the installation. My point is that with a service there is always more than one point where the grounded conductor is connected to the earth. The electrical issues are the same when you connect the output of a generator to earth at more than one point. Either the practice of bonding at more than one point is safe or it is a hazard. That fact does not change based on who is making the connections or what code applies.

There are a number of cases where CMP5 wants us to believe that the electrons behave differently based on what side of the service disconnect they are on.

 

[K8MHZ]

That doesn't have anything to do with my comment. The electrons behave the same way no matter what code governs the installation. My point is that with a service there is always more than one point where the grounded conductor is connected to the earth. The electrical issues are the same when you connect the output of a generator to earth at more than one point. Either the practice of bonding at more than one point is safe or it is a hazard. That fact does not change based on who is making the connections or what code applies.

There are a number of cases where CMP5 wants us to believe that the electrons behave differently based on what side of the service disconnect they are on.

I don't know how much difference it makes, but take note that, when using the utility as a comparison, there is only one grounded conductor going from the points to where the bonding takes place, not 2. The generator, on the other hand, would have two, as it's a four wire connection, not a three wire connection like the utility.

 

[reddy kw]

Portable Generator Bonding

Portable Generator Bonding

Doesn't connecting genset (with neutral bonded to frame) to house service using typical 2-pole x-sfer switch (only switching 'hot' phase conductors) create objectionable current flow, allowing current back flow (through service neutral) out to street potentially causing damage/injury?
Shouldn't (1) the neutral be disconnected from genset frame; (2) new grounding electrode (I.E. driven ground rod) and GEC for genset be installed; and a 3-pole pole double throw x-fer switch (switching neutral) be installed?
Isn't this why on permanently installed gensets the neutral is switched?
Isn't a "portable" genset connected to a permanent x-fer switch and permanent house wiring through 4-conductor cord set in effect a "separately derived system (I.E. genset never moved/used with extension cords on construction sites)? Homeowners are opting for larger (I.E. 10 KW) portable gensets (instead of permanently installed gensets) due to cost and other issues. These "portable" gensets are usually connected via hard-wired 2-pole x-fer switches to back up crutial circuits.
How is a 10 KW "portable" gasoline genset suppling phase, neutral and grounding conductors through 4-wire cordset to 1-family house any different (in practice as opposed to NEC's def) from a 100k kw standby diesel genset powering large building?

 

[don_resqcapt19]

Doesn't connecting genset (with neutral bonded to frame) to house service using typical 2-pole x-sfer switch (only switching 'hot' phase conductors) create objectionable current flow, allowing current back flow (through service neutral) out to street potentially causing damage/injury?

There may be some small amount of current through the parallel paths, but the only voltage that is available to drive this current is the voltage drop on the grounded conductor. This should not be enough to cause any safety issues.

Shouldn't (1) the neutral be disconnected from genset frame; (2) new grounding electrode (I.E. driven ground rod) and GEC for genset be installed; and a 3-pole pole double throw x-fer switch (switching neutral) be installed?

The code does not require that the neutral be switched if remove the bond at the generator. That is only required when the generator is set up as a SDS.

Isn't this why on permanently installed gensets the neutral is switched?

That is a design issue not a code issue. If the generator is set up as a SDS, then you need to switch the neutral. If it is not set up as a SDS the neutral is not switched. Most of the ones I have been involved with were not set up as SDS.

Isn't a "portable" genset connected to a permanent x-fer switch and permanent house wiring through 4-conductor cord set in effect a "separately derived system (I.E. genset never moved/used with extension cords on construction sites)? Homeowners are opting for larger (I.E. 10 KW) portable gensets (instead of permanently installed gensets) due to cost and other issues. These "portable" gensets are usually connected via hard-wired 2-pole x-fer switches to back up crutial circuits.

If the neutral is bonded at the generator then it is SDS.

How is a 10 KW "portable" gasoline genset suppling phase, neutral and grounding conductors through 4-wire cordset to 1-family house any different (in practice as opposed to NEC's def) from a 100k kw standby diesel genset powering large building?

Its not, but tell me why multiple bonding points on the line side of the service are permitted if that is such a big hazard.

 

[resistance]

I just installed a generator kit, and the portable generator (Champion) my customer has came with a floating neutral. So, they do come this way.

 

[reddy kw]

Its not, but tell me why multiple bonding points on the line side of the service are permitted if that is such a big hazard.

Margin of safety for linesmen. NEC doesn't cover utility company installations. NEC permits anything unless/until prohibited by revisions.

 

[kwired]

Margin of safety for linesmen. NEC doesn't cover utility company installations. NEC permits anything unless/until prohibited by revisions.

I think it has very little to do with safety of linesmen. Ground it once or ground it multiple times they are exposed to very high voltages either way. When they are working it live there is voltage between all the conductors whether any of them are grounded or not. It is grounded multiple times for lightning dissipation, and to help keep a consistant voltage to ground throughout the system. Earth is a good conductor. Earth is hard to make a low resistance connection to. The more connections you have the lower the overall resistance will be. If POCO has a high level of neutral current you will run into some problems as there will be voltage drop that presents itself between anything connected to the grounded conductors and earth - including customer secondary services that have their grounded conductors bonded to the primary neutral.

 

[K8MHZ]

Margin of safety for linesmen. NEC doesn't cover utility company installations. NEC permits anything unless/until prohibited by revisions.

Linesmen have the NESC in place of the NEC.

 

[don_resqcapt19]

Margin of safety for linesmen. NEC doesn't cover utility company installations. NEC permits anything unless/until prohibited by revisions.

I don't understand. Nothing in the NEC, NESC or utility rules tells us we have to have a transfer swtich that switches the grounded conductor when using a generator. What exactly would be the hazard to the linemen if the generator neutral conductor is bonded at the generator and at the building? How would this change if it was only bonded at the building?

 

[ceb58]

I don't understand. Nothing in the NEC, NESC or utility rules tells us we have to have a transfer swtich that switches the grounded conductor when using a generator. What exactly would be the hazard to the linemen if the generator neutral conductor is bonded at the generator and at the building? How would this change if it was only bonded at the building?

You are correct Don, nothing tells us to separate or not separate and there would be no hazard to the utility. Now lets get back to what the NEC tells us to do. If you hook a generator to the premise wiring then Art. 702 must be followed along with other articles that pertain to the installation such as Art.225, 250 and 445 to name a few. What the poco allows on the line side is no concern. We must be concerned with any thing after the load side connection to the meter.

 

[don_resqcapt19]

You are correct Don, nothing tells us to separate or not separate and there would be no hazard to the utility. Now lets get back to what the NEC tells us to do. If you hook a generator to the premise wiring then Art. 702 must be followed along with other articles that pertain to the installation such as Art.225, 250 and 445 to name a few. What the poco allows on the line side is no concern. We must be concerned with any thing after the load side connection to the meter.

I didn't ask what are the code rules.
I asked what is the real world hazard when a portable generator has its neutral conductor bonded at the generator and is conneted to the building wiring system with a transfer switch that does not switch the grounded conductor?

 

[reddy kw]

I didn't ask what are the code rules.
I asked what is the real world hazard when a portable generator has its neutral conductor bonded at the generator and is conneted to the building wiring system with a transfer switch that does not switch the grounded conductor?

You're right. 'Hot' and 'return' don't have to be part of the same circuit. Consensus seems to be: NESC and NEC cover all possibilities. Installations compliant with current codes can't be made better or safer. Mea culpa.

 

[kwired]

You're right. 'Hot' and 'return' don't have to be part of the same circuit. Consensus seems to be: NESC and NEC cover all possibilities. Installations compliant with current codes can't be made better or safer. Mea culpa.

I have no idea what you mean here. Especially the first sentence.

 

[ceb58]

I didn't ask what are the code rules.
I asked what is the real world hazard when a portable generator has its neutral conductor bonded at the generator and is conneted to the building wiring system with a transfer switch that does not switch the grounded conductor?

For services 800 amp or more the neutral must be switched due to GFI protection. For smaller systems the only hazard would be the parallel neutral caused by bonding at the gen. and not switching the neutral. If you lost the neutral from the gen. then you would put unwanted current back on the normally non-current carrying parts. As a hazard to linemen there wouldn't be any as the return current on the generator wants to return to its source.
The real world facts are it is not allowed, as you well know, the same as not allowing the same redundant bonding in sub-panels.