3P ATS

[m sleem]

Now let’s see what happens if there is a ground
fault at point A in Figure 4. The current will leave
at point A, it needs to find a way back to the
generator (along the neutral). Its only option is to flow along the ground and to get back into the system at the neutral-to-ground bond at the
service entrance (shown at point B).
Once back in the system, the ground-fault current
will flow along the neutral, through the solid
neutral in the ATS, back to the generator. Just like
during normal current flow, the algebraic sum of
the current through the generator’s ground-fault
sensor equals zero. This means that the ground
fault is not being picked up by the ground-fault
sensor on the generator. The ground-fault sensor
in a generator is often integrated into the circuit
breaker, so in this case the breaker will not open
during a ground fault. In fact, the ground fault may
not be correctly sensed by the system until the
ATS returns to utility power. (It might be seen at
the normal-source breaker, causing the breaker
to trip,

I recalled this explanation from Kohler web site, The red mark is done by me,

My first question is"why there is no current will flow in the EGC even the generator neutral is not bonded?"

Second question "why still the algebraic sum of the current through the generator’s ground-fault sensor equals zero despite of the presence of ground fault?"

 

[m sleem]

Any feedback!!

 

[ron]

For the circuit to complete, the current wants to go back to its source's neutral. This assumes the gen is the active source.

The current will not travel on the EGC from the ATS to the gen, because there is no connection at the gen to the neutral (no N-G bond) so thereal is no path.

The sum is still 0 because all the current leaving the ungrounded conductorso are returning through the neutral at the gen breaker (although via the utility breaker / ATS path)

 

[steve66]

It goes to ground, back through the N-G bond in the utility breaker, and back on the neutral to the generator. The arrows pretty much show the path A to B and back to the gen.

And what Ron said - the same current flows out from the gen on the phase, and back into the gen on the neutral

 

[m sleem]

...
The sum is still 0 because all the current leaving the ungrounded conductorso are returning through the neutral at the gen breaker (although via the utility breaker / ATS path)

But sum will not be zero in case of the presence of ground fault!

Am i missing something here?

 

[steve66]

But sum will not be zero in case of the presence of ground fault!

Am i missing something here?

yes, it will be zero. There is no current flowing back to the generator on the generators ground wire. It all flows on the neutral.

the generators ground doesn’t connect to anything at the generator except the frame and ground. There would be nowhere for current returning on the ground wire to go. It can’t all build up on the frame. And it can’t go back to ground - that’s where it came from.

It it needs to find a way back to the source, and the neutral is the only path.

 

[kwired]

But sum will not be zero in case of the presence of ground fault!

Am i missing something here?

If you want the GF protection to sense non zero you need to have the neutral grounded at the generator(ahead of the GF detection). If you do that you now have a SDS situation and need to switch the neutral in the transfer switch, GF protection is one reason to use SDS.

 

[ron]

But sum will not be zero in case of the presence of ground fault!

A ground fault doesn't give the electrons any special place to hide or go other than another path toward their source neutral - which in this case is through the neutral at the gen breaker via the utility breaker / ATS path.

 

[m sleem]

A ground fault doesn't give the electrons any special place to hide or go other than another path toward their source neutral - which in this case is through the neutral at the gen breaker via the utility breaker / ATS path.

Thanks Ron,

Maybe it needs another post,

I read before about the objectionable current which is generated by a wrong connection between neutral and EGC in load side which lead a part of return current to run in EGC then goes back to neutral in service panel,

My confusion because the code requests to connect communication grounding to main grounding on earth while also recommended to disconnect some points between communication grounding and main grounding due to objectionable current,
I understand from this, the generated objectionable current could flow back to earth then goes to communication systems in building which is not required,

From code justification, the objectionable current could go to different paths not just back to the source through bonded neutral.,

 

[kwired]

Thanks Ron,

Maybe it needs another post,

I read before about the objectionable current which is generated by a wrong connection between neutral and EGC in load side which lead a part of return current to run in EGC then goes back to neutral in service panel,

My confusion because the code requests to connect communication grounding to main grounding on earth while also recommended to disconnect some points between communication grounding and main grounding due to objectionable current,
I understand from this, the generated objectionable current could flow back to earth then goes to communication systems in building which is not required,

From code justification, the objectionable current could go to different paths not just back to the source through bonded neutral.,

In your drawing there is unlimited possibilities for potential paths to get from "A" to "B". That is normal for any code compliant bonding and equipment grounding arrangements. There is only one path for current to flow from the main bonding jumper back to the generator neutral though, and because of how that setup is drawn it won't trip the GFP either. Any trip would be on overcurrent only and not GFP function.

 

[m sleem]

In your drawing there is unlimited possibilities for potential paths to get from "A" to "B". That is normal for any code compliant bonding and equipment grounding arrangements. There is only one path for current to flow from the main bonding jumper back to the generator neutral though, and because of how that setup is drawn it won't trip the GFP either. Any trip would be on overcurrent only and not GFP function.

But current and electrons are not running from positive to negative anymore

 

[kwired]

But current and electrons are not running from positive to negative anymore

Right, they flow negative to positive