Separately derived system

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hhsting

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Glen bunie, md, us
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Junior plan reviewer
I have 3MW generator three phase 480 V and all the loads that it’s feeding is three phase balanced load. This generator is standby and is feeding bunch of 3 phase chillers, 3 phase HVAC equipment for big building that has cell phone switch tenant. Note: This Generator Does NOT feed Fire Pump.

So there is three phase conductor and equipment going to the downstream ATS that is 4 poles.

Following questions:

1. Is neutral required to be brought in from the generator to the ATS per NEC 2014?

2. How can the separately derived generator be grounded and bonded if no neutral is brought based on NEC 2014 Section 250.30?

3. If anyone experience with this sort of thing how is generator grounded and bonded NEC 2014 Section 250.30?




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Not much information.
The gen is 480, 3ph
The ATS is 4 pole.
There are no 277V, 1 ph loads

From this one would suspect:
The utility feeding the ATS is 4Wire Wye, solidly grounded
The Utility neutral is switched in the ATS

Is this true? If not what is the utility system?
I will need this to continue.
 
If the generator is a grounded system, and there are no line to neutral loads, you will have to bring an EGC or a supply side bonding jumper from the generator to the transfer switch. It would be an EGC if there is an OCPD at the generator and a SSBJ if there is not. If it is not a grounded system, you will have to provide ground detectors.
 
don_resqcapt19 said:
If the generator is a grounded system, and there are no line to neutral loads, you will have to bring an EGC or a supply side bonding jumper from the generator to the transfer switch. It would be an EGC if there is an OCPD at the generator and a SSBJ if there is not. If it is not a grounded system, you will have to provide ground detectors.
Click to expand...

Let’s say it’s grounded system and provide EGC. What about system bonding jumper at the generator? Should their be one?


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electrofelon said:
Hint: 250.30(A)(1)
Click to expand...

Ok 250.30(A)(1)(a): system bonding jumper shall connect the grounded conductor to the supply side bonding jumper and normally non current carrying metal enclosure.

In my case their is no neutral or grounded conductor I guess from gen to ATS. All I have is supply side bonding jumper from ATS to the generator and 3 phase conductors. Thus the question how can their be system bonding jumper?


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Confirm please, the generator has no neutral terminal or connection point (its 480 Delta only) , correct ?
 
hhsting said:
Ok 250.30(A)(1)(a): system bonding jumper shall connect the grounded conductor to the supply side bonding jumper and normally non current carrying metal enclosure.

In my case their is no neutral or grounded conductor I guess from gen to ATS. All I have is supply side bonding jumper from ATS to the generator and 3 phase conductors. Thus the question how can their be system bonding jumper?


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Click to expand...

I bet you a dollar there is an OCPD or a disconnect at the generator. In that case that is where the system bonding jumper goes.

augie47 said:
Confirm please, the generator has no neutral terminal or connection point (its 480 Delta only) , correct ?
Click to expand...

Yeah that needs clarification. I see the options as:
1. 480 delta ungrounded
2. 480 delta corner grounded
3. 277/480 wye point grounded.
 
iceworm said:
... From this one would suspect:
The utility feeding the ATS is 4Wire Wye, solidly grounded
The Utility neutral is switched in the ATS

Is this true? If not what is the utility system?
I will need this to continue.
Click to expand...

Let’s say it’s grounded system and provide EGC. What about system bonding jumper at the generator? Should their be one
Click to expand...

LarryFine said:
We also need to know the characteristics of the existing service.
Click to expand...
Ya think?

Not any help from me on this one - sorry
 
Keep in mind the OP has stated in the past that he only wants responses from knowledgeable people.

JAP>
 
then I'm doing the right thing.
Tried to help.
Figured out I was not knowledgeable on this system.
Bowed out while reminding the OP that more information was necessary for anyone to have a knowledgeable response
 
iceworm said:
then I'm doing the right thing.
Tried to help.
Figured out I was not knowledgeable on this system.
Bowed out while reminding the OP that more information was necessary for anyone to have a knowledgeable response
Click to expand...

Everyone on this forum is knowledgeable about something.
Its the accumulation of responses that leads to the answer whether knowledgeable responses or not.

JAP>
 
don_resqcapt19 said:
If the generator is a grounded system, and there are no line to neutral loads, you will have to bring an EGC or a supply side bonding jumper from the generator to the transfer switch. It would be an EGC if there is an OCPD at the generator and a SSBJ if there is not. If it is not a grounded system, you will have to provide ground detectors.
Click to expand...

In addition, there would need to be a GEC that terminates to the grounded conductor somewhere close to the generator.
 
hummmm .... You are chewing me out because I am acknowledging I don't have a knowledgeable response?
Okay

Its the accumulation of responses that leads to the answer whether knowledgeable responses or not.
Click to expand...
Or did I get that wrong and 157 unknowledgeable responses (unless it takes 327) will yield a credible answer?
Okay

Rhetorical Questions. Ignoring is a reasonable response

And the worm turneth and begins to dig
 
iceworm said:
hummmm .... You are chewing me out because I am acknowledging I don't have a knowledgeable response?
Okay


Or did I get that wrong and 157 unknowledgeable responses (unless it takes 327) will yield a credible answer?
Okay

Rhetorical Questions. Ignoring is a reasonable response

And the worm turneth and begins to dig
Click to expand...

Not at all.

I was Just poking a little fun at the OP since on an earlier thread he had indicated he wanted responses from "Knowledgeable People".

It was quite comical at the time seeing as how some of the most knowledgeable folks associated with the electrical trade chime in on this forum.

My response had nothing to do with your response.

I will be the first to admit I sometimes chime in with unknowledgeable responses, but, the replies to those responses usually get us the information needed to get to the answer.

It's the back and forth that usually gets us the answers of why things are done a certain way in the NEC.

Jap>
 
Ok I have updated plans which now I can post update for questions that were posted by various members:


Please see attached sketch. Their is no neutral brought either side of ATSnormal side or generator side. All load is three phase balanced i.e no neutral load.

The generator is 480/277V, three phase, wye grounded, separately derived and outside building. The generator has 4000A breaker which feeds by 10 sets of 4#600 kcmil to SWBD B. The SWBD B has 4000A main breaker, the N to G bond is in SWBD B and from SWBD B ground bus bar grounding electrode conductor to gnd bar which goes to building grounding electrodes.

There are 2 feeder breakers 1600A in SWBD B each has 4 sets of 600kcmil with 500 kcmil gnd , No neutral, to two ATSs.

The two ATSs are 3 pole and EGC are directly connected no neutral brought either side.

Should not N to G bond be in Generator the gen 4000A breaker first disco not in SWBD B?

Anyways Going back to post #1 questions can anyone please help me.

I appreciate all your help sorry for my ignorance.
 

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hhsting said:
Ok I have updated plans which now I can post update for questions that were posted by various members:


Please see attached sketch. Their is no neutral brought either side of ATSnormal side or generator side. All load is three phase balanced i.e no neutral load.

The generator is 480/277V, three phase, wye grounded, separately derived and outside building. The generator has 4000A breaker which feeds by 10 sets of 4#600 kcmil to SWBD B. The SWBD B has 4000A main breaker, the N to G bond is in SWBD B and from SWBD B ground bus bar grounding electrode conductor to gnd bar which goes to building grounding electrodes.

There are 2 feeder breakers 1600A in SWBD B each has 4 sets of 600kcmil with 500 kcmil gnd , No neutral, to two ATSs.

The two ATSs are 3 pole and EGC are directly connected no neutral brought either side.

Should not N to G bond be in Generator the gen 4000A breaker first disco not in SWBD B?

Anyways Going back to post #1 questions can anyone please help me.

I appreciate all your help sorry for my ignorance.
Click to expand...

Bump


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Okay I think I see what you have here. This system has no imbalance loads so no neutral is pulled in any of the circuits or feeders....including the service feeds. So, to answer question number 1 in your opening post, no you don't need to pull a neutral.

For question number two we have to discuss terminology. Grounding refers to creating a conductive path on which fault currents can travel back to source in the event a fault occurs. So, you need to connect your generator grounding system to the building grounding system via your grounding (not grounded or neutral) conductor(s). Bonding has to do with selecting the correct location in the system to tie your neutral (grounded) conductor system to the grounding conductor system. So, in this case since there is no neutral, there is no bond. (for now anyway)

Now this brings up the next question. So what do we do with the neutral connection in the generator (center of the "y" winding connection). And here is were the bad news might rear its ugly head. So in order to know how this will work we MUST know how the building service is grounded. If this is a "wye-connected" service then you would simply "ground" the generator windings using the neutral connection. This is technically a bond, but it cannot create a parallel path for current flow in the grounding system since no neutral current is possible.

However, if the building is fed from a delta configuration that is corner grounded, then the generator would also need to be corner grounded on one of the phases. This can be done on a Wye wound alternator head. But in order to do this the generator head would need to be rated for and configured for this type of connection. Specifically, with one leg tied to ground the other two legs would create 480V measured to ground. The Wye-wound head may only be rated for 277V to ground.

So, in your case, I would first check the normal power supplys feeding the transfer switches to see how they are configured (grounding wise). If its a 277/480V Wye system I'd bond the neutral to ground at both the generator head and at SWBD B so long as no neutral is present and no imbalance load is (or will be) present. If it's a corner grounded system then I'd be talking to the manufacturer of the generator to determine if it can be used in the application.

I wrote all of this for three reasons
1) to generate a discussion that will, I hope, get you to a solution
2) to test myself on my own understanding of how one would deal with this situation
3) to learn from this great group of folks about where I might be in error...so please fire away if I am wrong on any of this!
 
RD35 said:
...
For question number two we have to discuss terminology. Grounding refers to creating a conductive path on which fault currents can travel back to source in the event a fault occurs. So, you need to connect your generator grounding system to the building grounding system via your grounding (not grounded or neutral) conductor(s). Bonding has to do with selecting the correct location in the system to tie your neutral (grounded) conductor system to the grounding conductor system. So, in this case since there is no neutral, there is no bond. (for now anyway)
...
Click to expand...

errg. No. Stop. 🤦‍♂️

Grounding is (ultimately) a connection to earth. It stabilizes voltage to earth but does not "create a conductive path on which fault currents can travel back to source." Bonding is what creates that path. In this case that path is apparently allowed to go either to the generator neutral point or through ground detectors.

I agree with your point that the service and generator should be grounded the same way if both are grounded.

See apparently related thread here: https://forums.mikeholt.com/threads/no-neutral.2552810/
 
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