480 volt 3 phase generator bonding

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I have a 480 volt 4 wire Y Gnd. service to a main disconnect in which it is bonded at that point. It is then brought into a 3 pole transfer switch the neutral conductor is not brought to the transfer switch but there is a EGC connected. From my generator there are 3 ungrounded conductors and a ECG landed in the transfers switch as well. There has been no bonding of the neutral bus and ground bus in the generator . The way I see it this is defined as a separately derived system and there is not an effective ground fault current path on the generator supplied system. I need to install a bonding jumper in the generator and add GEC to correct this installation . Am I missing Something?
 

GoldDigger

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Why is there no neutral from generator to switch? Is it also a grounded wye source?
If you bond the neutral at the generator and run only an EGC you will have a fault current path but may not be code compliant.
Do you have any line to neutral loads? If you do, your scheme will result in normal current traveling on the EGC, which is not allowed.
 

ActionDave

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I have a 480 volt 4 wire Y Gnd. service to a main disconnect in which it is bonded at that point. It is then brought into a 3 pole transfer switch the neutral conductor is not brought to the transfer switch but there is a EGC connected. From my generator there are 3 ungrounded conductors and a ECG landed in the transfers switch as well. There has been no bonding of the neutral bus and ground bus in the generator . The way I see it this is defined as a separately derived system and there is not an effective ground fault current path on the generator supplied system. I need to install a bonding jumper in the generator and add GEC to correct this installation . Am I missing Something?
What you have described is not an SDS. You have a NON-SDS and the neutral should be floated at the generator.
 

texie

Senior Member
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Fort Collins, Colorado
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Electrician, Contractor, Inspector
I have a 480 volt 4 wire Y Gnd. service to a main disconnect in which it is bonded at that point. It is then brought into a 3 pole transfer switch the neutral conductor is not brought to the transfer switch but there is a EGC connected. From my generator there are 3 ungrounded conductors and a ECG landed in the transfers switch as well. There has been no bonding of the neutral bus and ground bus in the generator . The way I see it this is defined as a separately derived system and there is not an effective ground fault current path on the generator supplied system. I need to install a bonding jumper in the generator and add GEC to correct this installation . Am I missing Something?

It seems to me that since you have a wye service that is grounded and you have a 3 pole ATS I don't see any other safe and compliant way to do this except to run the neutrals from the service AND the generator at least to the ATS and leave the neutral floating at the genset. If you don't do this you will not have a fault return path to the genset source and while running on genset you will be operating from an ungrounded source. This would be a non-SDS setup and you can't do it as a SDS because you are not switching the neutral. Another issue I see here is the ATS itself. If you have it connected on the normal side to a grounded wye source it would typically be a 480/277 (208/120 as the case may be) switch and require a neutral to operate correctly and the emergency side would have to be the same.
Assuming you have NO line to neutral load the neutrals would not have to go beyond the ATS.
 
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It seems to me that since you have a wye service that is grounded and you have a 3 pole ATS I don't see any other safe and compliant way to do this except to run the neutrals from the service AND the generator at least to the ATS and leave the neutral floating at the genset. If you don't do this you will not have a fault return path to the genset source and while running on genset you will be operating from an ungrounded source. This would be a non-SDS setup and you can't do it as a SDS because you are not switching the neutral. Another issue I see here is the ATS itself. If you have it connected on the normal side to a grounded wye source it would typically be a 480/277 (208/120 as the case may be) switch and require a neutral to operate correctly and the emergency side would have to be the same.
Assuming you have NO line to neutral load the neutrals would not have to go beyond the ATS.

Gentlemen, forgive my slow understanding of this what is the reason for me having to bring a neutral conductor to the ATS? If I have no neutral loads can it not stop at the first disconnect of each source? Also, I understand that if there was a neutral conductor pulled to the ATS from both sources and not switched then it would be a Non SDS. If the neutrals are not brought to equipment (granted that is ok) then there is No physical connection between the two systems right?
 

ron

Senior Member
I agree with DLaHaye. Bond N-G at the generator and no neutral is brought from the gen to the ATS (there are no L-N loads and it is not a service disconnect).

I would also guess a GEC is also needed at the Gen to the grounding electrode system, but I'd have to dig for a code reference.

 

kwired

Electron manager
Location
NE Nebraska
Gentlemen, forgive my slow understanding of this what is the reason for me having to bring a neutral conductor to the ATS? If I have no neutral loads can it not stop at the first disconnect of each source? Also, I understand that if there was a neutral conductor pulled to the ATS from both sources and not switched then it would be a Non SDS. If the neutrals are not brought to equipment (granted that is ok) then there is No physical connection between the two systems right?

The presence of normal operating current on the grounded conductor is one of the main keys to the requirements.

By not utilizing the neutral for any loads you sort of mess with the general practice with a transfer switch a little.

Sending a neutral and an EGC to the transfer switch if there is no load on the neutral is sort of pointless. The fact you never open the neutral conductor in the transfer switch still makes it a non separately derived system.
 

kwired

Electron manager
Location
NE Nebraska
Since no neutral is brought to the ATS, it is always open :)

I gave that a little more thought and the other thing that comes into play here is the bonding location for the generator supplied system.

I did not read applicable sections, but the general idea behind them that I am aware of is to eliminate the potential of the EGC and or bonded equipment from carrying neutral current. We have no neutral current to worry about in OP's situation but without reading it I probably better keep quiet as I am not really sure exactly what it may require in this instance. Ordinarily for the non SDS the service bonding jumper is the point where bonding the generator system neutral and EGC are also bonded, not in the generator or even at the tranfer switc unless the TS is also the service equipment.
 

chris kennedy

Senior Member
Location
Miami Fla.
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60 yr old tool twisting electrician
What type of ATS operates with out a neutral for controls?
Sorry, OP never stated ATS
 
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kwired

Electron manager
Location
NE Nebraska
What type of ATS operates with out a neutral for controls?
Sorry, OP never stated ATS
One with line to line voltage control circuit. I can't say how common that may be though, but seems for certain if it were corner grounded delta there would be no other choice, but then if that were what op had this discussion would be a little different as the grounded conductor is going to be a current carrying conductor in that case.
 
The presence of normal operating current on the grounded conductor is one of the main keys to the requirements.

By not utilizing the neutral for any loads you sort of mess with the general practice with a transfer switch a little.

Sending a neutral and an EGC to the transfer switch if there is no load on the neutral is sort of pointless. The fact you never open the neutral conductor in the transfer switch still makes it a non separately derived system.

Okay, but if the neutral conductors are not connected together would that not be same as if they were switched?
 

kwired

Electron manager
Location
NE Nebraska
Okay, but if the neutral conductors are not connected together would that not be same as if they were switched?

If you ground/bond both "systems" there is continuity between them, even intentionally separately derived systems.

What we try to avoid is having a grounded current carrying conductor AND parallel paths over equipment grounding conductors, raceways, and other components we don't intend to carry current under normal conditions. Location of system bonding jumper is critical to keep from having incorrect paths for grounded conductor currents.

Now take OP situation where there is no intentional current on the grounded conductor - and there isn't such problems. But I did not go to the book and read up on exactly what may or may not be permitted in this situation. In theory it makes no sense to run a neutral and a ground conductor when neither is going to carry current under normal operation. NEC could have other ideas about it though.
 
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